MATERIALS AND METHODS FOR USING AN ACYL-ACYL CARRIER PROTEIN THIOESTERASE AND MUTANTS AND CHIMERAS THEREOF IN FATTY ACID SYNTHESIS
A method of increasing production of fatty acids comprising introducing into a host cell or organism and expressing therein an acyl-acyl carrier protein (ACP) thioesterase (TE) from Bryantella formatexigens or a mutant thereof; a method of making a mutant B. formatexigens acyl-ACP TE; a method of making a chimeric Cuphea viscosissima acyl-ACP TE; a nucleic acid encoding a mutant acyl-ACP TE or a chimeric C. viscosissima acyl-ACP TE; a host cell or organism comprising the nucleic acid; a mutant acyl-ACP TE or chimeric C. viscosissima acyl-ACP TE; a method of altering the specificity of a plant acyl-ACP TE; and a method of altering the level of activity of a plant acyl-ACP TE.
This application is a divisional of co-pending U.S. patent application Ser. No. 13/558,323, which was filed on Jul. 25, 2012, with a claim of priority to U.S. provisional patent application No. 61/512,373 filed on Jul. 27, 2011, both of which are hereby incorporated by reference in their entireties.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENTThe work described herein was supported, at least in part, by The National Science Foundation under contract no. EEC0813570. Therefore, the Government of the United States of America has certain rights in the invention.
TECHNICAL FIELDThe present disclosure relates to enzymes, mutants and chimeras thereof, fatty acid synthesis, nucleic acids, proteins and host cells and organisms.
BACKGROUNDDe novo fatty acid biosynthesis can be considered an iterative “polymerization” process, commonly primed with the acetyl moiety from acetyl-CoA and with iterative chain extension occurring by reaction with malonyl-acyl carrier protein (ACP). In most organisms this process optimally produces 16- and 18-carbon (C16 and C18) fatty acids. The enzyme that determines fatty acid chain length is acyl-ACP thioesterase (TE). This enzyme catalyzes the terminal reaction of fatty acid biosynthesis, acyl-ACP thioester bond hydrolysis (i.e., the hydrolysis of the thioester bond between the acyl chain and the sulfhydryl group of the phosphopantetheine prosthetic group of ACP), to release a free fatty acid and ACP. This reaction terminates acyl-chain elongation of fatty acid biosynthesis and, therefore, determines fatty acid chain length. It is also the biochemical determinant of the fatty acid composition of storage lipids in plant seeds.
In discrete phyla and/or tissues of specific organisms (primarily higher plant seeds), thioester hydrolysis optimally produces medium-chain (C8-C14) fatty acids (MCFAs), which have wide industrial applications (e.g., producing detergents, lubricants, cosmetics, and pharmaceuticals) (Dehesh et al., Plant Physiol. 110: 203-210 (1996)). TEs that specifically hydrolyze medium-chain acyl-ACP substrates have been studied widely (Dehesh et al. (1996), supra; Voelker et al., Science 257: 72-74 (1992)); and Yuan et al., PNAS USA 92: 10639-10643 (1995)). Short-chain fatty acids (SCFAs; e.g., butanoic acid and hexanoic acid) have more recently gained importance as potential bio-renewable chemicals that could be derived from the fatty acid biosynthesis pathway (Nikolau et al., Plant J. 54: 536-545 (2008)). As a critical acyl chain termination enzyme, acyl-ACP TEs with desired substrate specificities are, therefore, important for engineering this pathway.
To date, dozens of acyl-ACP TEs have been functionally characterized and sorted into two classes, FatA and FatB (Jones et al., Plant Cell 7: 359-371 (1995)). FatA-class TEs act on long-chain acyl-ACPs, preferentially on oleoyl-ACP (Jones et al. (1995), supra; Hawkins et al., Plant J. 13: 743-752 (1998); Serrano-Vega et al., Planta 221: 868-880 (2005); and Sanchez-Garcia et al., Phytochemistry 71: 860-869 (2010)), while FatB-class TEs preferably hydrolyze acyl-ACPs with saturated fatty acyl chains (Jones et al. (1995), supra). The archetypical FatB-class TE was isolated from the developing seeds of California bay (Umbellularia californica). This enzyme is specific for 12:0-ACP, and it plays a critical role in MCFA production (Voelker et al. (1992), supra; and Pollard et al., Arch Biochem. Biophys. 284: 306-312 (1991)). This discovery spurred isolation of additional MCFA-specific TEs from Cuphea (Dehesh et al. (1996), supra; Dehesh et al. Plant J. 9: 167-172 (1996); and Leonard et al., Plant Mol. Biol. 34: 669-679 (1997)), Arabidopsis thaliana (Dormann et al., Arch Biochem. Biophys. 316: 612-618 (1995)), Myristica fragrans (nutmeg) (Voelker et al., Plant Physiol. 114: 669-677 (1997)), and Ulmus americana (elm) (Voelker et al. (1997), supra).
Recently, TEs obtained from public databases were classified into 23 families based on sequence and three-dimensional structure similarity (Cantu et al., Protein Sci. 19: 1281-1295 (2010)). These TEs were defined as enzymes that can hydrolyze any thioester bond irrespective of the chemical nature of the carboxylic acid and thiol molecules that constitute the substrates of these enzymes. The TE sequences are collected in the constantly updated ThYme database (www.enzyme.cbirc.iastate.edu; Cantu et al., Nucleic Acids Res. 39: D342-346 (2011), which is hereby incorporated by reference). Of these 23 families, Family TE14 contains plant and bacterial acyl-ACP TEs involved in Type II fatty acid synthesis, the reactions of which are catalyzed by discrete mono-functional enzymes. Family TE14 contained 360 unique sequences as of late 2010, but only ˜7% of these sequences had been functionally characterized, and all of those were FatA and FatB TEs from higher plants. The remaining ˜220 bacterial acyl-ACP TEs were mostly generated from genomic sequencing projects and had not been functionally characterized.
Alteration of the substrate specificity of plant TEs has been described by Yuan et al. (U.S. Pat. Nos. 5,955,329 and 6,150,512, which are incorporated herein by reference for their teachings regarding same) and Roessler et al. (U.S. Pat. App. Pub. No. 2011/0020883, which is hereby incorporated by reference for its teachings regarding same). Yuan et al. identifies the C-terminal two-thirds portion of plant TEs as desirable for modification. Roessler et al. discloses a plant acyl-ACP thioesterase of a specified sequence (sequence identification no. 29) in which amino acid 174, alone or in further combination with amino acid 103, is mutated.
In view of the foregoing, the present disclosure seeks to provide methods of using acyl-ACP TE and mutants and chimeras thereof, in particular bacterial and plant acyl-ACP TE and mutants and chimeras thereof, to alter substrate specificity and/or alter activity (e.g., increase production of fatty acids) in a host cell or organism. These and other objects and advantages, as well as additional inventive features, will become apparent from the detailed description provided herein.
SUMMARYA method of increasing production of fatty acids, such as short-chain fatty acids and/or fatty acids having from about six carbons to about 12 carbons, such as from about 10 carbons to about 12 carbons (e.g., fatty acids having less than about 10 carbons or fatty acids having less than about 12 carbons) in a host cell or organism is provided. The method comprises introducing into the host cell or organism and expressing therein a nucleic acid molecule comprising a nucleotide sequence encoding an acyl-acyl carrier protein (ACP) thioesterase (TE) from Bryantella formatexigens.
Another method of increasing production of fatty acids, such as short-chain fatty acids and/or fatty acids having from about six carbons to about 12 carbons, such as from about 10 carbons to about 12 carbons (e.g., fatty acids having less than about 10 carbons or fatty acids having less than about 12 carbons) in a host cell or organism is also provided. The method comprises introducing into the host cell or organism and expressing therein a nucleic acid molecule comprising a nucleotide sequence encoding a mutant acyl-ACP TE derived from wild-type Bryantella formatexigens acyl-ACP TE, wherein the mutant acyl-ACP TE produces more fatty acids, such as short-chain fatty acids, in the host cell or organism that the corresponding wild-type acyl-ACP TE.
Also provided is a method of making a mutant Bryantella formatexigens acyl-ACP TE. The method comprises making a mutant Bryantella formatexigens acyl-ACP TE comprising two or more amino acid mutations comprising N169Y and S222I.
An isolated or purified nucleic acid molecule is also provided. The nucleic acid molecule comprises a nucleotide sequence encoding a mutant acyl-ACP TE, which is derived from wild-type Bryantella formatexigens acyl-ACP TE, comprises two or more amino acid mutations comprising N169Y and S222I, and has increased thioesterase activity compared to wild-type Bryantella formatexigens acyl-ACP TE. The isolated or purified nucleic acid molecule can be a vector.
Also provided is a host cell or organism. The host cell or organism comprises the above-described nucleic acid molecule comprising a nucleotide sequence encoding a mutant acyl-ACP TE.
Further provided is an isolated or purified mutant acyl-ACP TE. The mutant acyl-ACP TE is derived from wild-type Bryantella formatexigens acyl-ACP TE, comprises two or more amino acid mutations comprising N169Y and S222I, and has increased thioesterase activity compared to wild-type Bryantella formatexigens acyl-ACP TE.
A method of making a chimeric Cuphea viscosissima acyl-ACP TE gene is also provided. The method comprises replacing a segment of a wild-type Cuphea viscosissima acyl-ACP TE with a segment of another acyl-ACP TE.
Further provided is another isolated or purified nucleic acid molecule. The nucleic acid molecule comprises a nucleotide sequence encoding a chimeric Cuphea viscosissima acyl-ACP TE gene, which comprises a segment of another acyl-ACP TE gene. The isolated or purified nucleic acid molecule can be a vector.
Still further provided is another host cell or organism. The host cell or organism comprises the above-described isolated or purified nucleic acid molecule comprising a nucleotide sequence encoding a chimeric Cuphea viscosissima acyl-ACP TE gene.
Even still further provided is an isolated or purified chimeric Cuphea viscosissima acyl-ACP TE. The chimera comprises a segment of another acyl-ACP TE.
A method of altering the specificity of a plant acyl-ACP TE for at least one of its substrates is also provided. The method comprises introducing into the plant acyl-ACP TE a substrate specificity-altering mutation in the region corresponding to amino acids 118-167 of the mature amino acid sequence of the Cuphea viscosissima acyl-ACP TE encoded by FatB2. The method can comprise mutating at least one amino acid corresponding to an amino acid selected from the group consisting of amino acid 133, amino acid 142, and amino acid 143 of the mature amino acid sequence of the Cuphea viscosissima acyl-ACP TE encoded by FatB2. The method can further comprise mutating at least one amino acid corresponding to an amino acid selected from the group consisting of amino acid 110 and amino acid 184 of the mature amino acid sequence of the Cuphea viscosissima acyl-ACP TE encoded by FatB2. The method can further comprise altering the level of activity of the plant acyl-ACP TE by a method comprising mutating at least one amino acid corresponding to an amino acid selected from the group consisting of amino acid 173, amino acid 176, and amino acid 205 of the mature amino acid sequence of the Cuphea viscosissima acyl-ACP TE encoded by FatB2.
In view of the foregoing, a method of altering the level of activity of a plant acyl-ACP TE is also provided. The method comprises mutating at least one amino acid corresponding to an amino acid selected from the group consisting of amino acid 173, amino acid 176, and amino acid 205 of the mature amino acid sequence of the Cuphea viscosissima acyl-ACP TE encoded by FatB2. The method can further comprise altering the specificity of the plant acyl-ACP TE by a method comprising introducing into the plant acyl-ACP TE a substrate specificity-altering mutation in the region corresponding to amino acids 118-167 of the mature amino acid of the Cuphea viscosissima acyl-ACP TE encoded by FatB2. The method can comprise mutating at least one amino acid corresponding to an amino selected from the group consisting of amino acid 133, amino acid 142, and amino acid 143 of the mature amino acid sequence of the Cuphea viscosissima acyl-ACP TE encoded by FatB2. The method can further comprise mutating at least one amino acid corresponding to an amino acid selected from the group consisting of amino acid 110 and amino acid 184 of the mature amino acid sequence of the Cuphea viscosissima acyl-ACP TE encoded by FatB2.
Yet another isolated or purified nucleic acid molecule is provided. The isolated or purified nucleic acid molecule comprises a nucleotide sequence encoding a mutant plant acyl-ACP TE, which comprises a substrate specificity-altering mutation in the region corresponding to amino acids 118-167 of the mature amino acid sequence of the Cuphea viscosissima acyl-ACP TE encoded by FatB2. The isolated or purified nucleic acid molecule can be a vector. The encoded mutant plant acyl-ACP TE can comprise a mutation of at least one amino acid corresponding to an amino acid selected from the group consisting of amino acid 133, amino acid 142, and amino acid 143 of the mature amino acid sequence of the Cuphea viscosissima acyl-ACP TE encoded by FatB2. The encoded mutant plant acyl-ACP TE can further comprise a mutation of at least one amino acid corresponding to an amino acid selected from the group consisting of amino acid 110 and amino acid 184 of the mature amino acid sequence of the Cuphea viscosissima acyl-ACP TE encoded by FatB2. The encoded mutant plant acyl-ACP TE can further comprise a level of activity-altering mutation of at least one amino acid corresponding to an amino acid selected from the group consisting of amino acid 173, amino acid 176, and amino acid 205 of the mature amino acid sequence of the Cuphea viscosissima acyl-ACP TE encoded by FatB2.
Still yet another isolated or purified nucleic acid molecule is provided. The isolated or purified nucleic acid molecule comprises a nucleotide sequence encoding a mutant plant acyl-ACP TE, which comprises a level of activity-altering mutation of at least one amino acid corresponding to an amino acid selected from the group consisting of amino acid 173, amino acid 176, and amino acid 205 of the mature amino acid sequence of the Cuphea viscosissima acyl-ACP TE encoded by FatB2. The isolated or purified nucleic acid molecule can be a vector. The encoded mutant plant acyl-ACP TE can further comprise a substrate specificity-altering mutation in the region corresponding to amino acids 118-167 of the mature amino acid of the Cuphea viscosissima acyl-ACP TE encoded by FatB2. The encoded mutant plant acyl-ACP TE can comprise a mutation of at least one amino acid corresponding to an amino acid selected from the group consisting of amino acid 133, amino acid 142, and amino acid 143 of the mature amino acid sequence of the Cuphea viscosissima acyl-ACP TE encoded by FatB2. The encoded mutant plant acyl-ACP TE can further comprise a substrate specificity-altering mutation of at least one amino acid corresponding to an amino acid selected from the group consisting of amino acid 110 and amino acid 184 of the mature amino acid sequence of the Cuphea viscosissima acyl-ACP TE encoded by FatB2.
Another host cell or organism is provided. The host cell or organism comprises the above-described isolated or purified nucleic acid molecule comprising a nucleotide sequence encoding a mutant plant acyl-ACP TE, which comprises a substrate specificity-altering mutation in the region corresponding to amino acids 118-167 of the mature amino acid sequence of the Cuphea viscosissima acyl-ACP TE encoded by FatB2.
An isolated or purified mutant plant acyl-ACP TE is also provided. The isolated or purified mutant plant acyl-ACP TE comprises a substrate specificity-altering mutation in the region corresponding to amino acids 118-167 of the mature amino acid sequence of the Cuphea viscosissima acyl-ACP TE encoded by FatB2. The mutant TE can comprise a mutation of at least one amino acid corresponding to an amino acid selected from the group consisting of amino acid 133, amino acid 142, and amino acid 143 of the mature amino acid sequence of the Cuphea viscosissima acyl-ACP TE encoded by FatB2. The mutant TE can further comprise a substrate specificity-altering mutation of at least one amino acid corresponding to an amino acid selected from the group consisting of amino acid 110 and amino acid 184 of the mature amino acid sequence of the Cuphea viscosissima acyl-ACP TE encoded by FatB2. The mutant TE can further comprise a level of activity-altering mutation of at least one amino acid corresponding to an amino acid selected from the group consisting of amino acid 173, amino acid 176, and amino acid 205 of the mature amino acid sequence of the Cuphea viscosissima acyl-ACP TE encoded by FatB2.
Yet another isolated or purified mutant plant acyl-ACP TE is provided. The isolated or purified mutant plant acyl-ACP TE comprises a level of activity-altering mutation of at least one amino acid corresponding to an amino acid selected from the group consisting of amino acid 173, amino acid 176, and amino acid 205 of the mature amino acid sequence of the Cuphea viscosissima acyl-ACP TE encoded by FatB2. The mutant TE can further comprise a substrate specificity-altering mutation in the region corresponding to amino acids 118-167 of the mature amino acid of the Cuphea viscosissima acyl-ACP TE encoded by FatB2. The mutant TE can comprise a mutation of at least one amino acid corresponding to an amino acid selected from the group consisting of amino acid 133, amino acid 142, and amino acid 143 of the mature amino acid sequence of the Cuphea viscosissima acyl-ACP TE encoded by FatB2. The mutant TE can further comprise a substrate specificity-altering mutation of at least one amino acid corresponding to an amino acid selected from the group consisting of amino acid 110 and amino acid 184 of the mature amino acid sequence of the Cuphea viscosissima acyl-ACP TE encoded by FatB2.
The present disclosure is predicated, at least in part, on the discovery that expression of an acyl-acyl carrier protein (ACP) thioesterase (TE) from Bryantella formatexigens (DSM 14469, EET61113.1, ZP—05345975.3, C6LDQ9; Wolin et al., Appl. Environ. Microbiol. 69(10): 6321-6326 (October 2003); nucleotide sequence is SEQ ID NO: 23; amino acid sequence is SEQ ID NO: 24) in a host cell or organism, such as Escherichia coli, results in an increase in the production of short-chain fatty acids in the host cell or organism. In this regard, it has been surprisingly and unexpectedly discovered that the introduction of two or more point mutations in the acyl-ACP TE of B. formatexigens has a synergistic effect on short-chain activity in the host cell or organism. The present disclosure is further predicated on the discovery that the substrate specificity and activity (e.g., total amount of fatty acids produced) of an acyl-ACP TE, such as a plant acyl-ACP TE, can be affected by introducing a substrate specificity-altering mutation in the region corresponding to amino acids 118-167, such as from about amino acid 118 to about amino acid 167, of the mature amino acid sequence of the Cuphea viscosissima acyl-ACP TE encoded by FatB2. The materials and methods have application for biofuels, industrial lubricants, food oils, and the like.
In view of the foregoing, a method of increasing production of fatty acids, such as short-chain fatty acids and/or fatty acids having from about six to about 12 carbon atoms (C6-C12), such as fatty acids having from about 10 to about 12 carbon atoms (C10-C12), in a host cell or organism is provided. Thus, the method can be used to increase production of fatty acids having less than about 10 carbon atoms or fatty acids having less than about 12 carbon atoms. The method comprises introducing into the host cell or organism and expressing therein a nucleic acid molecule comprising a nucleotide sequence encoding an acyl-ACP TE, such as an acyl-ACP TE from
Another method of increasing production of fatty acids, such as short-chain fatty acids and/or fatty acids having from about six to about 12 carbon atoms (C6-C12), such as fatty acids having from about 10 to about 12 carbon atoms (C10-C12), in a host cell or organism is also provided. The method comprises introducing into the host cell or organism and expressing therein a nucleic acid molecule comprising a nucleotide sequence encoding a mutant acyl-ACP TE derived from a wild-type acyl-ACP TE, such as an acyl-ACP TE from
A method of making a mutant Bryantella formatexigens acyl-ACP TE is also provided. The method comprises making a mutant Bryantella formatexigens acyl-ACP TE comprising two or more amino acid mutations comprising N169Y and S222I. Preferably, and even desirably, the mutant Bryantella formatexigens acyl-ACP TE has increased thioesterase activity compared to a corresponding wild-type Bryantella formatexigens acyl-ACP TE. Mutant acyl-ACP TEs can be derived from such wild-type acyl-ACP TEs in accordance with methods known in the art and exemplified herein.
Also provided is a method of making a chimeric Cuphea viscosissima acyl-ACP TE. Any suitable method of making a chimera as known in the art and exemplified herein can be used. The method can comprise replacing a segment of a wild-type Cuphea viscosissima acyl-ACP TE with a segment of another acyl-ACP TE. Examples of wild-type Cuphea viscosissima acyl-ACP TEs include those encoded by the FatB1 gene (designated CvFatB1) and the FatB2 gene (designated CvFatB2). Any suitable acyl-ACP TE (see, e.g.,
A method of altering the specificity of a plant acyl-ACP TE for at least one of its substrates is also provided. For example, the specificity of a plant acyl-ACP TE for at least one of its substrates can be increased or decreased, even eliminated. The method comprises introducing into the plant acyl-ACP TE a substrate specificity-altering mutation in the region corresponding to amino acids 118-167, such as from about amino acid 118 to about amino acid 167, of the mature amino acid sequence of the Cuphea viscosissima acyl-ACP TE encoded by FatB2 (see, SEQ ID NO:3 in
In view of the foregoing, a method of altering the level of activity of a plant acyl-ACP TE is also provided. For example, the activity level, e.g., thioesterase activity level, such as the total amount of fatty acids produced, of the plant acyl-ACP TE can be increased or decreased compared to the activity level of the corresponding wild-type TE. An alteration in the level of activity can be an increase in fatty acid production or a decrease in fatty acid production, irrespective of whether or not the mol percentage of each fatty acid changes or not. Preferably, even desirably, the level of activity of the plant acyl-ACP TE is increased, rather than decreased. The method comprises mutating at least one amino acid corresponding to an amino acid selected from the group consisting of amino acid 173, amino acid 176, and amino acid 205 of the mature amino acid sequence of the Cuphea viscosissima acyl-ACP TE encoded by FatB2. Mutating amino acid 173 to F, mutating amino acid 176 to L, mutating amino acid 205 to F, or a combination of two or more of the foregoing can alter the level of activity of the plant acyl-ACP TE, such as increase the level of activity of the plant acyl-ACP TE. The method can further comprise altering the specificity of the plant acyl-ACP TE by a method comprising introducing into the plant acyl-ACP TE a substrate specificity-altering mutation in the region corresponding to amino acids 118-167 of the mature amino acid sequence of the Cuphea viscosissima acyl-ACP TE encoded by FatB2. The method can comprise mutating at least one amino acid corresponding to an amino acid selected from the group consisting of amino acid 133, amino acid 142, and amino acid 143 of the mature amino acid sequence of the Cuphea viscosissima acyl-ACP TE encoded by FatB2. Mutating amino acid 133 to F or L can increase production of C8 fatty acids, mutating amino acid 133 to V or A can increase production of C14/16 fatty acids, mutating amino acid 142 to A and mutating amino acid 143 to S can increase production of C8 fatty acids, and mutating both of amino acids 142 and 143 to R can increase production of C14/16 fatty acids. The method can further comprise mutating at least one amino acid corresponding to an amino acid selected from the group consisting of amino acid 110 and amino acid 184 of the mature amino acid sequence of the Cuphea viscosissima acyl-ACP TE encoded by FatB2. Mutating amino acid 110 to F can increase production of C4/6 fatty acids, mutating amino acid 110 to L can increase production of C8 fatty acids, mutating amino acid 110 to V can increase production of C14/16 fatty acids, and mutating amino acid 184 to F can increase production of C8 fatty acids.
Also in view of the foregoing, an isolated or purified nucleic acid molecule comprising a nucleotide sequence encoding a mutant acyl-ACP TE derived from a wild-type acyl-ACP TE, such as an acyl-ACP TE from
Further in view of the foregoing, an isolated or purified nucleic acid molecule comprising a nucleotide sequence encoding a chimeric Cuphea viscosissima acyl-ACP TE gene, which comprises a segment of another acyl-ACP TE gene, is provided. Any suitable acyl-ACP TE gene can serve as the source of the segment that is used to replace the segment of the wild-type Cuphea viscosissima acyl-ACP TE gene (see, e.g.,
Still further in view of the foregoing, an isolated or purified nucleic acid molecule comprising a nucleotide sequence encoding a mutant plant acyl-ACP TE, which comprises a substrate specificity-altering mutation in the region corresponding to amino acids 118-167, such as from about amino acid 118 to about amino acid 167, of the mature amino acid sequence of the Cuphea viscosissima acyl-ACP TE encoded by FatB2, is provided. Alternatively, the region can correspond to amino acids 110-184, such as from about amino acid 110 to about amino acid 184, of the mature amino acid of the Cuphea viscosissima acyl-ACP TE encoded by FatB2. Also, alternatively, the region can correspond to amino acids 110-205, such as from about amino acid 110 to about amino acid 205, of the mature amino acid of the Cuphea viscosissima acyl-ACP TE encoded by FatB2. Any suitable plant acyl-ACP TE gene can be mutated (see, e.g.,
Still yet another isolated or purified nucleic acid molecule is provided. The isolated or purified nucleic acid molecule comprises a nucleotide sequence encoding a mutant plant acyl-ACP TE, which comprises a level of activity-altering mutation (e.g., a mutation that alters the total amount of fatty acids produced, such as increases the total amount of fatty acids produced) of at least one amino acid corresponding to an amino acid selected from the group consisting of amino acid 173, amino acid 176, and amino acid 205 of the mature amino acid sequence of the Cuphea viscosissima acyl-ACP TE encoded by FatB2. Any suitable plant acyl-ACP TE gene can be mutated (see, e.g.,
Mutations, such as substitutions, insertions, deletions, and/or side chain modifications, can be introduced into the nucleotide and amino acid sequences of the acyl-ACP TE using any suitable technique known in the art, including site-directed mutagenesis (Wu, ed., Meth. Enzymol. 217, Academic Press (1993)). Alternatively, domains can be swapped between acyl-ACP TE genes (for example, when creating chimeras). Non-naturally occurring nucleotides and amino acids also can be used. Mutations to the nucleotide sequence should not place the sequence out of reading frame and should not create complementary regions that could produce secondary mRNA structures. The mutant or chimeric acyl-ACP TE may have altered substrate specificity, e.g., reacts with an acyl-ACP substrate that differs in chain length, degree of saturation, or presence/absence of a side group (e.g., methyl group), from that which is acted upon by the wild-type (also referred to as “native”) acyl-ACP TE. Alternatively, the mutant or chimeric acyl-ACP TE may have altered relative substrate specificity between two or more substrates, both of which are acted upon by the wild-type acyl-ACP TE. Both types of alterations in substrate specificity are encompassed by references to alterations of substrate specificity and substrate specificity-alterating mutations herein. Alternatively or additionally to altered substrate specificity, the mutant or chimeric acyl-ACP TE may have an altered activity level, e.g., level of thioesterase activity, such as the total amount of fatty acids produced, including increased or decreased activity. Altered substrate specificity and altered activity can be detected by expression of the mutant thioesterase in E. coli, for example, and assay of enzyme activity.
A nucleotide sequence encoding all or a part of an acyl-ACP TE can be chemically synthesized, such as by the phosphoramidite method (Beaucage et al., Tetrahedron Letters 22: 1859-1869 (1981); and Matthes et al., EMBO J. 3: 801-805 (1984)). Polynucleotides can be synthesized, purified, annealed to their complementary strand, ligated, and then, optionally, cloned into suitable vectors.
The isolated or purified nucleic acid molecule comprising a nucleotide sequence encoding a wild-type/mutant/chimeric acyl-ACP TE can be a vector. The vector can contain, and preferably does contain, transcription and translation control regions. A promoter can be constitutive or regulatable, such as inducible. Additional sequences that can be present in the vector include pre-processing sequences, such as transit peptide sequences and plastid transit peptide sequences.
The acyl-ACP TEs and mutant/chimeric acyl-ACP TEs identified herein can be used in whole or in part as probes in hybridization assays to identify other TEs that can be used in the methods described herein. The TEs or fragments thereof also can be used as primers to amplify target DNA, such as by polymerase chain reaction (PCR) and other nucleic acid amplification methods. See, e.g., Sambrook et al., Molecular Cloning: A Laboratory Manual, 3rd ed., Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y. (2001); Ausubel et al., eds., Short Protocols in Molecular Biology, 5th ed., John Wiley & Sons (2002).
The nucleic acid molecule comprising a nucleotide sequence encoding an acyl-ACP TE or a mutant/chimeric acyl-ACP TE can be introduced into a host cell or a host organism using any suitable technique as is known in the art. See, e.g., Sambrook et al., Molecular Cloning: A Laboratory Manual, 3rd ed., Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y. (2001); Ausubel et al., eds., Short Protocols in Molecular Biology, 5th ed., John Wiley & Sons (2002). Such methods include microinjection, DNA particle bombardment, electroporation, liposome fusion, Agrobacterium-mediated transformation, and methods exemplified herein. Depending on the host cell or the host organism, one method can be preferred over another as readily appreciated by one of ordinary skill in the art. The nucleotide sequence can be codon-optimized for the recipient host cell or organism.
In view of the above, a host cell comprising an above-described isolated or purified nucleic acid molecule is also provided. The host cell or organism can be any suitable host cell or organism. The host cell or organism can be prokaryotic or eukaryotic, unicellular or multicellular, and undifferentiated or differentiated. If large-scale production of short-chain fatty acids is desired, e.g., as a source of biofuel, bacteria (see, e.g., U.S. Pat. App. Pub. No. 2012/0164700, which discloses examples of cyanobacteria, and U.S. Pat. App. Pub. No. 2009/0298143, which discloses methods of expression in bacteria, and both of which are hereby incorporated by reference for their teachings regarding same), yeast (see, e.g., U.S. Pat. App. Pub. No. 2011/0294174, which discloses examples of yeast in Table 26 and other fungi in Table 27 and which is hereby incorporated by reference for its teachings regarding same), and algae (see, e.g., U.S. Pat. App. Pub. No. 2011/0294174, which discloses examples of algae in Table 1 and which is hereby incorporated by reference for its teachings regarding same; also, see U.S. Pat. No. 7,935,515 and U.S. Pat. App. Pub. No. 2012/0164700, which disclose methods of expressing TEs in microalgae and examples of microalgae and which are hereby incorporated by reference for their teachings regarding same; see, also, U.S. Pat. App. Pub. No. 2009/0317878, which is hereby incorporated by reference for its teachings regarding expression of genes in algae) can be preferred. A preferred bacterium is Escherichia coli, in particular the strain K27. A preferred yeast is Saccharomyces cerevisiae. Alternatively, a crop plant (e.g., maize), such as an oilseed crop plant or a seed cell thereof, can be preferred (see, e.g., U.S. Pat. No. 7,504,563, which discloses expression of a nucleic acid encoding a thioesterase in soybean seed and which is incorporated herein for its teachings regarding same). See, also, U.S. Pat. App. Pub. No. 2010/0154293, which discloses other examples of host cells in paragraph [0080] and which is incorporated herein by reference for its teachings regarding same.
Fatty acids can be harvested, or otherwise collected (e.g., isolation from media containing bacteria that secrete the fatty acids), from host cells or organisms by any convenient method. Cells can be lysed/disrupted (e.g., heat, enzymes, ultrasound, mechanical lysis, osmotic shock, acid/base addition, or infection with a lytic virus), and fatty acids can be separated from cell mass by centrifugation and extraction (e.g., extraction with hydrophobic solvent, liquefaction, supercritical CO2 extraction, or hexane extraction after freeze-drying and pulverization) and further processed/refined as necessary. See, e.g., U.S. Pat. No. 7,935,515 and U.S. Pat. App. Pub. No. 2012/0135479, which are incorporated specifically by reference for their teachings regarding same.
An isolated or purified mutant acyl-ACP TE derived from a wild-type acyl-ACP TE, such as an acyl-ACP TE from
An isolated or purified chimeric Cuphea viscosissima acyl-ACP TE, which comprises a segment of another acyl-ACP TE, is also provided. Any suitable acyl-ACP TE can serve as the source of the segment that is used to replace the segment of the wild-type Cuphea viscosissima acyl-ACP TE (see, e.g., an acyl-ACP TE from
An isolated or purified mutant plant acyl-ACP TE, which comprises a substrate specificity-altering mutation in the region corresponding to amino acids 118-167, such as from about amino acid 110 to about amino acid 167, of the mature amino acid sequence of the Cuphea viscosissima acyl-ACP TE encoded by FatB2, is also provided. Alternatively, the region can correspond to amino acids 110-184, such as from about amino acid 110 to about amino acid 184, of the mature amino acid of the Cuphea viscosissima acyl-ACP TE encoded by FatB2. Also, alternatively, the region can correspond to amino acids 110-205, such as from about amino acid 110 to about amino acid 205, of the mature amino acid of the Cuphea viscosissima acyl-ACP TE encoded by FatB2. The mutant TE can comprise a mutation of at least one amino acid corresponding to an amino acid selected from the group consisting of amino acid 133, amino acid 142, and amino acid 143 of the mature amino acid sequence of the Cuphea viscosissima acyl-ACP TE encoded by FatB2. The mutant TE can further comprise a mutation of at least one amino acid corresponding to an amino acid selected from the group consisting of amino acid 110 and amino acid 184 of the mature amino acid sequence of the Cuphea viscosissima acyl-ACP TE encoded by FatB2. The mutant TE can further comprise a level of activity-altering mutation of at least one amino acid corresponding to an amino acid selected from the group consisting of amino acid 173, amino acid 176, and amino acid 205 of the mature amino acid sequence of the Cuphea viscosissima acyl-ACP TE encoded by FatB2.
Yet another isolated or purified mutant plant acyl-ACP TE is provided. The isolated or purified mutant plant acyl-ACP TE comprises a level of activity-altering mutation of at least one amino acid corresponding to an amino acid selected from the group consisting of amino acid 173, amino acid 176, and amino acid 205 of the mature amino acid sequence of the Cuphea viscosissima acyl-ACP TE encoded by FatB2. The mutant TE can further comprise a substrate specificity-altering mutation in the region corresponding to amino acids 118-167, such as from about amino acid 118 to about amino acid 167, of the mature amino acid of the Cuphea viscosissima acyl-ACP TE encoded by FatB2. Alternatively, the region can correspond to amino acids 110-184, such as from about amino acid 110 to about amino acid 184, of the mature amino acid of the Cuphea viscosissima acyl-ACP TE encoded by FatB2. Also, alternatively, the region can correspond to amino acids 110-205, such as from about amino acid 110 to about amino acid 205, of the mature amino acid of the Cuphea viscosissima acyl-ACP TE encoded by FatB2. The mutant TE can comprise a mutation of at least one amino acid corresponding to an amino acid selected from the group consisting of amino acid 133, amino acid 142, and amino acid 143 of the mature amino acid sequence of the Cuphea viscosissima acyl-ACP TE encoded by FatB2. The mutant TE can further comprise a substrate specificity-altering mutation of at least one amino acid corresponding to an amino acid selected from the group consisting of amino acid 110 and amino acid 184 of the mature amino acid sequence of the Cuphea viscosissima acyl-ACP TE encoded by FatB2.
Once sequenced, polypeptides can be synthesized using methods known in the art, such as, for example, exclusive solid phase synthesis, partial solid phase synthesis, fragment condensation, and classical solution synthesis. See, e.g., Merrifield, J. Am. Chem. Soc. 85: 2149 (1963), and Stewart and Young in Solid Phase Peptide Syntheses (2nd Ed., Pierce Chemical Company, 1984). Automated peptide synthesizers are commercially available, as are services that make peptides to order.
EXAMPLESThe following examples serve to illustrate the present disclosure. The examples are not intended to limit the scope of the claimed invention in any way.
Example 1This example describes the functional characterization of diverse acyl-ACP TEs rationally chosen based on phylogenetic classification of the TEs.
Sequences from Family TE14 (Cantu et al. (2010), supra) in the ThYme database (www.enzyme.cbirc.iastate.edu) were downloaded from the GenBank (Benson et al., Nucleic Acids Res. 39 (suppl. 1): D32-D37 (2011)) and UniProt (UniProt Consortium: The universal protein resource (UniProt) in 2010, Nucleic Acids Res. 38: D142-D148 (2010)) databases. Fragments and incomplete sequences were removed, yielding 360 acyl-ACP TE sequences. A multiple sequence alignment (MSA) was generated from catalytic domains of these sequences using MUSCLE 3.6 (Edgar, Nucleic Acids Res. 32: 1792-1797 (2004)) with default parameters. An unrooted phylogenetic tree based on the MSA was built using Molecular Evolutionary Genetics Analysis 4 (MEGA4) (Tamura et al., Mol. Biol. Evol. 24: 1596-1599 (2007)).
The minimum evolution algorithm was used due to its high effectiveness with large data sets (Desper et al., J. Comput. Biol. 9: 687-705 (2002)), gaps were subjected to pairwise deletion, and an amino acid Jones-Taylor-Thornton (JTT) (Jones et al., Comput. Appl. Biosci. 8: 275-282 (1992)) distance model was chosen. The phylogenetic tree was further verified by a bootstrap test with 1,000 replicates. The bootstrapped consensus tree was qualitatively analyzed and broken into apparent subfamilies. Statistical analysis was conducted to show that all sequences within a subfamily were more closely related to each other than to sequences in other subfamilies. Based on the MSA, JTT distances between all sequences were calculated and arranged into a j×j matrix, where j is the total number of sequences. Inter-subfamily distances and variances were determined using this matrix. For each apparent subfamily, a smaller k×k matrix, where k is the number of sequences in a given subfamily, was calculated. From this, intra-subfamily mean distances and variances were determined. These values were applied to the following equation to determine z:
where
A z-value >3.3 between two subfamilies shows that the difference between them is statistically significant top <0.001. If a z-value between two apparent subfamilies were <3.3, alternative apparent subfamilies were chosen and/or individual sequences were removed, and the statistical calculations were repeated. Subfamilies were finally defined with a phylogenetic tree in which all z-values exceeded 3.3, sometimes leaving some sequences outside any subfamily (i.e. non-grouped sequences) (see Table 2).
All sequences within individual subfamilies were aligned using MUSCLE 3.6, and rooted phylogenetic trees were built in MEGA4 with the same tree and bootstrap parameters as described above. A few sequences from another subfamily (that with the highest z-value) were chosen to root individual subfamily trees.
A total of 360 amino acid sequences belonging to Family TE14 (Cantu et al. (2010), supra) were subjected to phylogenetic analysis and grouped into subfamilies. A subfamily is defined as having at least five sequences from different species, and it must pass the statistical tests described in the experimental procedures. Ten subfamilies met these criteria, accounting for 326 TE sequences; in addition 34 TE sequences could not be grouped into any of these subfamilies. All z-values were >3.4, ranging from 3.41 to 29.7, and mean distances between different subfamilies were larger than those within subfamilies.
Family TE14 contains acyl-ACP TEs that had previously been characterized from plants and classified into two types, FatA and FatB (Jones et al. (1995), supra). Of the ten subfamilies identified, Subfamilies A, B, and C are comprised of acyl-ACP TEs found in plants. All experimentally characterized sequences previously classified as FatB acyl-ACP TEs make up ˜25% of Subfamily A, which contains 81 angiosperm-sourced sequences. The coconut and C. viscosissima acyl-ACP TEs identified also belong to this subfamily. Subfamily B, which comprises 21 sequences primarily sourced from angiosperms as well as from the moss Physcomitrella patens, represents a potentially novel plant acyl-ACP TE subfamily with no previous experimental or phylogenetic characterization. Plant FatA acyl-ACP TEs, which act on long-chain acyl-ACP molecules, especially oleoyl-ACP (Jones et al. (1995), supra), belong to the 32-member Subfamily C. As with Subfamily B, the six green algal sequences from Chlamydomonas, Ostreococcus, and Micromonas that comprise Subfamily D have not been experimentally characterized.
Unlike several plant acyl-ACP TEs, no bacterial acyl-ACP TEs had been previously functionally characterized. A total of 186 bacterial acyl-ACP TE sequences were classified into six subfamilies (Subfamily E-Subfamily J). All 17 acyl-ACP TE sequences from gram-negative bacteria are in Subfamily E, which includes sequences from halophilic (Salinibacter and Rhodothermus), sulfate-reducing (Desulfovibrio, Desulfohalobium, and Desulfonatronospira), chemo-organotrophic (Spirosoma), metal-reducing (Anaeromyxobacter, Geobacter, and Pelobacter), and marine (Microscilla) bacteria. Subfamily F consists of 24 sequences, mainly from Bacteroides but also from other related bacteria. Protein Data Bank (PDB) structure 2ESS, obtained from a structural genomic effort, is part of this subfamily. Subfamily G and Subfamily H have 31 and 27 sequences, respectively, primarily from Clostridium. Subfamily I is comprised of eight sequences from six genera. Gram-positive lactic acid bacteria, almost completely from the genera Lactobacillus, Enterococcus, and Streptococcus, are part of Subfamily J (79 sequences). PDB:2OWN, the second bacterial acyl-ACP TE structure obtained from a structural genomic effort, appears in this family. Although the two known Family TE14 crystal structures (PDB:2ESS in Subfamily F and PDB:2OWN in Subfamily J) are from organisms in widely separated subfamilies, they are highly similar, as may be expected since they are members of the same enzyme family.
Some Family TE14 sequences are not grouped into any subfamily because their inclusion decreased z-values below acceptable limits. These include two plant and four moss sequences adjacent to Subfamilies A and C, and 28 bacterial sequences more closely related to Subfamilies E to I. No experimental work had previously been done on any of these sequences.
Upon generating the phylogenetic relationships among the 360 acyl-ACP TE sequences predicted or experimentally placed in Family TE14, 25 were chosen for experimental characterization. Of these, the cDNA for 24 was synthesized, while the cDNA of the Elaeis guineensis (oil palm) acyl-ACP TE was isolated from a phage cDNA library previously constructed from mRNA isolated from the developing fruit of Indonesian-sourced oil palm.
The selection of acyl-ACP TEs to characterize was based upon the primary structure-based phylogenetic relationships among the enzymes, along with knowledge of the fatty acid profile of the source organisms of these acyl-ACP TEs. Briefly, at least one TE was characterized from each of the ten subfamilies except for Subfamily C, whose members appear to be specific for oleoyl-ACP substrates. For subfamilies that contain acyl-ACP TEs originating from organisms without any known fatty acid data, or from organisms where acyl-ACP TEs were not previously characterized, acyl-ACP TE sequences that are evolutionarily distant from each other within each subfamily were selected for further investigation. For example, within Subfamily A there are two distinct and separate groupings of acyl-ACP TEs that are derived from the Poaceae family, for which there is no functional characterization (see Table 2). One grouping contains one sorghum acyl-ACP TE sequence (GenBank:EER87824) and the other contains two (GenBank:EER88593 and GenBank:EES04698). To explore this structural divergence as an indicator of potential functional divergence in substrate specificities, one each of these Subfamily A sorghum acyl-ACP TEs (GenBank:EER87824 and GenBank:EER88593) and the two Subfamily B sorghum acyl-ACP TEs were expressed and functionally characterized.
Example 2This example describes the cloning of acyl-ACP TEs from Cocus nucifera (coconut) and Cuphea viscosissima.
Coconut fruits of different developmental stages were obtained from the USDA-ARS-SHRS National Germplasm Repository (Miami, Fla., USA). Seeds of C. viscosissima were obtained from the North Central Regional Plant Introduction Station (NCRPIS, Ames, Iowa, USA). They were treated overnight with 0.1 mM gibberellic acid and then germinated in a growth chamber (Environmental Growth Chambers, Chagrin Falls, Ohio) with 12 hours of illumination at 25° C. followed by 12 hours of darkness at 15° C. Seedlings were transplanted into soil and cultivated at NCRPIS. Seeds at different developmental stages were collected and flash-frozen in liquid nitrogen.
Acyl-ACP TE cDNAs were cloned from C. viscosissima and coconut via a homologous cloning strategy. MSAs of plant TE14 sequences revealed two conserved regions (RYPTWGD [SEQ ID NO: 7] and NQHVNNVK [SEQ ID NO: 8]), from which two degenerate primers, DP-F3 (5′-AGNTAYCCNACNTGGGGNGA-3′ [SEQ ID NO: 9]) and DP-R3 (5′-TACTTNACRTTRTTNACRTGYTGRTT-3′ [SEQ ID NO: 10]), were designed. RNA was extracted from endosperm of nearly mature coconuts and immature seeds of C. viscosissima using the total RNA (plant) kit (IBI Scientific, Peosta, Iowa, USA). RNA was reverse-transcribed to cDNA using the SuperScript™ first-strand synthesis system for RT-PCR kit (Invitrogen, Carlsberg, Calif., USA). PCR was performed in a 50 μL, reaction mixture containing 20 ng cDNA, 1×Pfx buffer, 1 mM MgSO4, 0.3 mM dNTP, 5.12 μM DP-F3 and DP-R3 primers, and 0.5 U Pfx polymerase (Invitrogen) using a cycling program of 94° C. for four minutes, 35 cycles of 94° C. for 30 seconds, 52° C. for 30 seconds and 72° C. for 45 seconds, and a final extension step of 72° C. for five minutes. The expected ˜350-bp products were identified by agarose gel electrophoresis, and their DNA bands were recovered using the QiaQuick gel extraction kit (Qiagen, Valencia, Calif., USA) and cloned into the pENTR TOPO TA vector (Invitrogen). Using primers designed from the sequences of the cloned 350-bp fragments, the 5′- and 3′-ends of the cDNAs were obtained using the SMARTer RACE (rapid amplification of the cDNA ends) cDNA amplification kit (Takara Bio, Otsu, Japan).
For each acyl-ACP TE sequence, the full-length cDNA, minus the N-terminal chloroplast transit peptide, was amplified by PCR with primers engineered to introduce Bam HI and Eco RI restriction sites at the 5′- and 3′-ends, respectively. The PCR-amplified products were digested with Bam HI and Eco RI and cloned into the corresponding restriction sites of the pUC57 vector, which placed the acyl-ACP TE sequence under the transcriptional control of the lacZ promoter. The sequence of each construct was confirmed by sequencing both strands. Confirmed expression vectors of coconut genes were transformed into E. coli strain K27, while sequences of C. viscosissima acyl-ACP TEs were synthesized after being codon-optimized for expression in E. coli using the OptimumGene codon optimization program provided by GenScript USA (Piscataway, N.J., USA).
MCFAs are abundant in the oil produced in fruits of coconut (i.e., predominantly C12 and C14 and a small amount (0.2-1%) of C6 fatty acids (Kumar et al., J. Food Qual. 32: 158-176 (2009); Kumar et al., Indian Coconut J. 37: 4-14 (2006); and Kumar et al., Trop. Agr. 81: 34-40 (2004)) and seeds of C. viscosissima (i.e., predominantly C8 and C10 fatty acids (Phippen et al., Ind. Crop Prod. 24: 52-59 (2006)). Therefore, acyl-ACP TEs in the seeds of these species are predicted to be specific for medium-chain acyl-ACPs. Acyl-ACP TE sequences were isolated from coconut and C. viscosissima by a homologous cloning strategy. Using degenerate primers, which were designed from conserved regions of plant TE14 family enzymes, a 350-bp fragment in the middle of the mRNAs was amplified from cDNA generated from both developing coconut endosperm and C. viscosissima seeds. Sequencing of cloned PCR products identified three new acyl-ACP TE sequences each from coconut and C. viscosissima. The full-length cDNA sequences were obtained by RACE for three acyl-ACP TEs [CnFatB1 (JF338903), CnFatB2 (JF338904), and CnFatB3 (JF338905)] from coconut and three [CvFatB1 (JF338906), CvFatB2 (JF338907), and CvFatB3 (JF338908)] from C. viscosissima.
The predicted open reading frames of coconut and C. viscosissima acyl-ACP TE cDNAs were identified. They encode pre-proteins of 412 to 423 amino acids, with calculated molecular weights of 45.8 to 46.5 kDa and theoretical pIs of 6.4 to 8.8. Plant acyl-ACP TEs are nuclear-encoded, plastid-targeted proteins with an N-terminal plastid-targeting peptide extension (Voelker et al. (1992), supra). For each of the cloned coconut and C. viscosissima acyl-ACP TEs, the putative plastid-targeting peptide cleavage site was located on the N-terminal side of the conserved sequence LPDW, as proposed for many other plant acyl-ACP TEs (Jones et al. (1995), supra; Sanchez-Garcia (2010), supra; Dormann et al. (1995), supra; Jha et al., Plant Physiol. Biochem. 44: 645-655 (2006); and Moreno-Perez et al., Plant Physiol. Biochem. 49: 82-87 (2011)). These yield predicted mature proteins of 323 to 331 amino acid residues (Huynh et al., Plant Physiol. Biochem. 40: 1-9 (2002)), with calculated molecular weights of 36.6 to 37.5 kDa and theoretical pIs of 5.4 to 7.3. Alignment of the deduced amino acid sequences of coconut and C. viscosissima acyl-ACP TE cDNAs showed that, except for the plastid-targeting peptide sequences and very near the C-terminus, the sequences are co-linear and share very high identity (63-86%) within a species. These sequences cluster within Subfamily A.
Example 3This example describes in vivo activity assays.
E. coli strain K27 contains a mutation in the fadD gene impairing β-oxidation of fatty acids, which results in the accumulation of free fatty acids in the growth medium (Klein et al., Eur. J. Biochem. 19: 442-450 (1971); and Overath et al., Eur. J. Biochem. 7: 559-574 (1969)). Each TE was expressed in E. coli K27, and free fatty acids that accumulated in the medium were extracted and analyzed. Four colonies for each construct were independently cultured in 2 mL LB medium supplemented with 100 mg/L carbicillin in 17-mL culture tubes. When the culture reached an OD600 of ˜0.7, the growth medium was replaced with 3 mL of M9 minimal medium (47.7 mM Na2HPO4, 22.1 mM KH2PO4, 8.6 mM NaCl, 18.7 mM NH4Cl, 2 mM MgSO4, and 0.1 mM CaCl2) supplemented with 0.4% glucose and 100 mg/1 carbicillin, and 10 μM isopropyl-β-D-thiogalactopyranoside (IPTG) was added to induce acyl-ACP TE expression. After 40 hours of cultivation, cells were pelleted, and free fatty acids in the supernatant were extracted essentially following a previously described method (Voelker et al., J. Bacteriol. 176: 7320-7327 (1994); and Mayer et al., BMC Plant Biol. 2007: 7 (2007)). Briefly, 2 mL of culture supernatant was supplemented with 10 μg heptanoic acid (7:0), 10 μg undecanoic acid (11:0), and 20 μg heptadecanoic acid (17:0) (Sigma-Aldrich, St. Louis, Mo., USA) as internal standards. The mixture was acidified with 20 μL of 1 M HCl, and 4 mL chloroform-methanol (1:1 vol/vol) was used to recover the fatty acids from the medium. After vortexing for 10 minutes and centrifuging at 1000×g for four minutes, the lower chloroform phase was transferred to a new tube and evaporated under a stream of N2 gas until the samples were concentrated to ˜300 μL. Samples (1 μL) were analyzed on an Agilent Technologies (Santa Clara, Calif., USA) 6890 Series gas chromatograph (GC) system used with an Agilent 5973 mass selective detector equipped with an Agilent CP-Wax 58 FFAP CB column (25 mm×0.15 mm×0.39 mm). The GC program followed an initial temperature of 70° C. for two minutes, ramped to 150° C. at 10° C./minute and held for three minutes, ramped to 260° C. at 10° C./minute, and held for 14 minutes. Final quantification analysis was performed with AMDIS software (National Institute of Standards and Technology). Determination of C4 to C8, C10 to C12, and >C12 fatty acid concentrations was based on the fatty acid internal standards 7:0, 11:0, and 17:0, respectively. The total concentration of fatty acids produced by each acyl-ACP TE was obtained by subtracting the concentration of fatty acid produced by E. coli expressing a control plasmid (pUC57) lacking a TE from that produced by E. coli expressing a given acyl-ACP TE sequence from the same vector. The three most abundant fatty acids produced by the control strain were 8:0 (2.0 nmol/ml), 14:0 (3.5 nmol/ml), and 16:0 (3.1 nmol/ml), and their levels were minimal compared to strains expressing acyl-ACP TEs. Compared to GC analyses of fatty acids after derivatization (e.g., methylation or butylation), the GC-MS method used non-derivatized free fatty acids, which is better optimized for analyzing short-chain fatty acids (e.g., 4:0, 6:0, 8:0, 10:0, 12:0, and 14:0). However, this method may be less sensitive for longer-chain fatty acids (e.g., 18:0 and 18:1).
Analysis of free fatty acids revealed possible peaks characteristic of 2-tridecanone. To further confirm this identification, retention times and MS spectra of the peaks in each sample were compared to a 2-tridecanone standard (Sigma-Aldrich).
All isolated acyl-ACP TE cDNAs were expressed in E. coli strain K27. Secreted fatty acids were analyzed with GC-MS, and the total fatty acid yield in the medium was used to represent the in vivo activities of these enzymes on acyl-ACPs, though it remains possible that some of these enzymes might also hydrolyze acyl-CoAs (Othman et al., Biochem. Soc. Trans. 28: 619-622 (2000)).
A total of 13 acyl-ACP TEs from Subfamily A were characterized, including single acyl-ACP TEs from Cuphea palustris (GenBank:AAC49179), U. americana (GenBank:AAB71731), and oil palm (E. guineensis, GenBank:AAD42220), two each from Iris germanica (GenBank:AAG43857 and GenBank:AAG43858) and Sorghum bicolor (GenBank:EER87824 and GenBank:EER88593), and three each from coconut and C. viscosissima. Total fatty acid concentrations produced by these acyl-ACP TEs are listed in Table 1, and the resulting fatty acid compositions are shown in
C. palustris acyl-ACP TE produced 97 mol % 8:0 and only 0.8 mol % 10:0 fatty acids (
The CvFatB1 and CvFatB3 TEs, for which corresponding cDNAs were isolated from the developing seeds of C. viscosissima produced MCFAs in E. coli, and CvFatB1 shows substrate specificity consistent with the fatty acid constituents present in the seed oil. The relative distributions of 8:0 and 10:0 fatty acids differ; CvFatB1 produced twice as much 8:0 compared to 10:0 fatty acid, whereas there is ˜fourfold more 10:0 fatty acid within C. viscosissima seed oil (Phippen et al., Ind. Crop Prod. 24: 52-59 (2006)).
Three acyl-ACP TEs from plant sources belonging to Subfamily B, including those from P. patens (GenBank:EDQ65090) and S. bicolor (GenBank:EER96252 and GenBank:EES11622), and one acyl-ACP TE from Subfamily D sourced from the alga Micromonas pusilla (GenBank:EEH52851), were similarly characterized. Total activity in E. coli expressing these acyl-ACP TEs varied from 9 to 380 nmol/mL (Table 1). These four acyl-ACP TEs showed similar substrate specificities, producing predominantly 14:0 (34-65 mol %) and 16:1 (23-37 mol %) fatty acids (
Eleven acyl-ACP TE sequences from Subfamilies E to J sourced from bacteria and three bacterial sequences that were not placed in any subfamily were characterized (Table 1 and
Interestingly, many bacterial acyl-ACP TEs, such as those from Desulfovibrio vulgaris (GenBank:ACL08376, Subfamily E), L. brevis (GenBank:ABJ63754, Subfamily J), L. plantarum (GenBank:CAD63310, Subfamily J), and Bdellovibrio bacteriovorus (GenBank:CAE80300, no subfamily), are part of the pathway that produces noticeable amounts of the methylketone 2-tridecanone through enzymatic hydrolysis of 3-keto-tetradecanoyl-ACP followed by chemical decarboxylation. B. bacteriovorus acyl-ACP TE produced the highest concentration of 2-tridecanone, 9.4 nmol/mL (
The accumulation of both unsaturated fatty acids and saturated fatty acids observed is consistent with the previous conclusion that the heterologously expressed acyl-ACP TEs can intercept both saturated and unsaturated intermediates of fatty acid biosynthesis of E. coli (Magnuson et al., Microbiol. Rev. 57: 522-542 (1993)). Interestingly, in the E. coli heterologous expression system used, six bacterial-sourced acyl-ACP TEs and three plant-sourced acyl-ACP TEs produced noticeable amounts (>1 nmol/mL) of methylketones, largely 2-tridecanone. The acyl-ACP TE from B. bacteriovorus (GenBank: CAE80300) produced the highest concentration of 2-tridecanone (9.4 nmol/mL).
Methylketones, such as 2-tridecanone, occur in the wild tomato species Solanum habrochaites subsp. Glabratum (Antonious, J. Environ. Sci. Health B 36: 835-848 (2001)), and their biosynthesis is catalyzed by two sequentially-acting methylketone synthases, MKS1 and MKS2. MKS2 is a thioesterase that catalyzes the hydrolysis of the 3-ketoacyl-ACP intermediate in fatty acid biosynthesis, and MKS1 catalyzes the decarboxylation of the released 3-keto acid to produce a methylketone (Ben-Israel et al., Plant Physiol. 151: 1952-1964 (2009); and Yu et al., Plant Physiol. 154: 67-77 (2010)). Heterologous expression of MKS2 in E. coli yields many methylketones, including 2-tridecanone (Yu et al. (2010), supra). However, MKS2 is not included in Family TE14; rather, it is included in Family TE9 (Cantu et al. (2010), supra). Although some Family TE14 members share very low, if any, significant sequence similarity (i.e., <15% identity) to MKS2, the data indicate that at least nine acyl-ACP TEs (e.g., B. bacteriovorus, GenBank:CAE80300) can catalyze the same reaction as MKS2 (i.e, hydrolysis of the thioester bond of 3-ketoacyl-ACP), and that the resulting product (3-keto acid) is further chemically or enzymatically decarboxylated to generate the methylketone.
Example 4This example describes statistical cluster analysis.
To classify acyl-ACP TEs based on their in vivo activities, the fatty acid composition data obtained from the in vivo expression of all TE sequences studied were used to perform statistical clustering analysis. The distance matrix was calculated using Euclidean distances, and Ward's method (Ward, J. Am. Stat. Assoc. 58: 236 (1963)) was used to perform agglomerative hierarchical clustering. The p-values were calculated via multiscale bootstrap re-sampling with 1,000 replicates (Suzuki et al., Bioinformatics 22: 1540-1542 (2006)).
All acyl-ACP TEs that were characterized were clustered into three classes: 1) Class I contains acyl-ACP TEs that mainly act on C14 and C16 substrates; 2) Class II has acyl-ACP TEs that have broad substrate specificities, with major activities toward C8 and C14 substrates; and 3) Class III comprises acyl-ACP TEs that predominantly act on C8 substrate (
Comparison between the specificity-based classification and the sequence-based phylogenetic tree indicates that the two classifications are not necessarily consistent with each other. Three phenomena were observed in this study. First, diverged sequences (variants in primary structure) from the same species do not necessarily differ in function. Second, similar sequences may have different substrate specificities. Third, sequences that belong to different subfamilies because they share low sequence identity can have very similar substrate specificities. Therefore, it is not reasonable to infer the substrate specificity of one acyl-ACP TE based on its sequence-based classification within the same subfamily. It is conceivable, therefore, that the change of substrate specificity is most likely caused by changes of only a few amino acid residues, and that many different combinations of residue changes could result in changed specificities (Jones (1995), supra). Bacterial orthologs provide access to additional functional diversity, both relative to acyl chain length specificity (e.g., shorter acyl chains, as short as four carbon atoms), as well as acyl chains that contain additional chemical functionalities (e.g., unsaturated acyl chains and acyl chains containing carbonyl groups).
Example 5This example describes the generation of random mutants and site-directed mutants of acyl-ACP TE EET61113.
DNA sequences for the wild-type acyl-ACP TE EET61113 was synthesized and cloned into pUC57 vector as previously. The random mutants were generated by error-prone PCR using primers designed on pUC57 vector (pUC57F: 5′-CTGCAAGGCGATTAAGTTGGGTAAC-3′ [SEQ ID NO: 11]; pUC57R: 5′-CGGCTCGTATGTTGTGTGGAAT-3′ [SEQ ID NO: 12]). The PCR was conducted in 40 tubes of reaction mixture (15 μl), which contained 1×PCR buffer, 0.2 mM dATP and dGTP, 1 mM dCTP and dTTP, 7 mM MgCl2, 0.1 mM MnCl2, 0.5 μl of each primers, 1.5 ng plasmid containing the thioesterase gene, and 0.15 U Taq DNA polymerase (Invitrogen), using a cycling program of 94° C. for 4 minutes, 31 cycles of 94° C. for 30 seconds, 52° C. for 30 seconds, and 72° C. for 1 minute, and a final extension step of 72° C. for 5 minutes. The PCR products were pooled together, purified with the QiaQuick gel extraction kit (Qiagen, Valencia, Calif., USA), digested with Bam HI and Eco RI, and then cloned into the corresponding restriction sites of the pUC57 vector. The constructed vectors containing mutant genes were transformed into E. coli K27 by electroporation.
Site-directed mutations were also introduced into wild-type acyl-ACP TE EET61113. Specifically, a mutant (designated TE20-N169Y), which contains a single N->Y mutation at amino acid position 169, and another mutant (designated TE20-S222I), which contains a single S->I mutation at amino acid position 222, were generated.
Example 6This example describes the initial screening of acyl-ACP TE mutants generated in Example 5.
Mutants were screened on Neutral Red-containing media, which was M9 minimal medium (47.7 mM Na2HPO4, 22.1 mM KH2PO4, 8.6 mM NaCl, 18.7 mM NH4Cl, 2 mM MgSO4, and 0.1 mM CaCl2) solidified by 15 g/L agar and supplemented with 0.4% glucose, 100 mg/L carbicillin, 1 mM IPTG, and 40 ppm Neutral Red. This screening method is based on pH change in the media. Mutants with higher acyl-ACP TE activity will produce more free fatty acids, which decrease the pH of the colonies and generate a more intense red color. Briefly, after electroporation, an appropriate amount of culture was spread on the Neutral Red plates so that each plate would contain 100-200 colonies. The plates were incubated at 30° C. for two days, and then at room temperature for another 3-5 days. Eventually, the colonies that are more intensely red were selected for further characterization with GC-MS.
Example 7This example describes the further characterization of those mutants that were identified in Example 6 as producing more fatty acids.
Colonies that were more intensely red on the Neutral Red plate were assumed to produce more fatty acids. The activity and composition of the mutants were characterized as described above with slight modification. Instead of 20 μl of 1 M HCl, 200 μl of 1 M HCl were used to acidify the cell culture supernatant, which allowed recovery of more butanoic acid from the sample. Thus, the activity of wild-type thioesterase EET61113 in this Example was higher than the production in the above Examples.
The in vivo activities of 139 mutants have been determined so far. Their total activitys are shown in
This example describes the construction of chimeric TEs.
CvFatB1 and CvFatB2 share 72% identity in their amino acid sequences, but have very different substrate specificities: CvFatB1 mainly produces C8 and C10 fatty acids, while CvFatB2 produces C14 and C16 fatty acids. Chimeric TEs were constructed using these two sequences to locate the region(s) that determine the substrate specificity of acyl-ACP TEs. Previously, CvFatB1 and CvFatB2 genes were codon-optimized, synthesized, and cloned into the pUC57 vector. Using the primers listed in Table 3, six fragments (I, II, III, IV, V, and VI) for each TE gene were generated (see
The chimeric TEs were constructed by re-assembling the six fragments to recreate the full-length thioesterase gene sequence by PCR, using a combination of fragments from either CvFatB1 or CvFatB2. PCR was performed in a 50 μL, reaction mixture containing 10 ng of each fragment, 1× Phusion buffer, 0.2 mM dNTP, 0.5 μM pUC57F and pUC57R primers, and 1 Unit of Phusion high-fidelity DNA polymerase (New England Biolabs) using a cycling program of 98° C. for 2 minutes, 32 cycles of 98° C. for 10 seconds, 50° C. for 15 seconds, and 72° C. for 20 seconds, and a final extension step of 72° C. for 5 minutes. The expected full-length gene products were identified by agarose gel electrophoresis, recovered from the gel using the QiaQuick gel extraction kit (Qiagen, Valencia, Calif.) and cloned into the pUC57 vector using the Bam HI and Eco RI restriction sites. The sequence of each construct was confirmed by sequencing using primers pUC57F and pUC57R.
Example 9This example describes the use of sequence alignments to identify residues that may affect substrate specificity.
A total of 27 representative acyl-ACP TE sequences, including both plant and bacterial TEs that were previously functionally characterized, were aligned using Vector NTI software (Invitrogen) with the default parameters. While Cysteine 264 was previously proposed to be a catalytic residue by Mayer et al. (J. Biol. Chem. 280: 3621-3627 (2005)), Cys264 was not conserved among these 27 TE sequences. The adjacent glutamic acid (Glu263), however, was conserved and predicted to be a catalytic residue. Multiple sequence alignment and phylogenetic analysis resulted in the identification of another nine residues that also may affect substrate specificities, namely residue 110 in Fragment II, residues 133 and 139 in Fragment III, and residues 173, 176, 184, 192, 198, and 205 in Fragment IV (see
This example describes the use of site-directed mutagenesis to verify residues that may affect substrate specificity.
Point mutants were generated from CvFatB2 with the QuikChange II site-directed mutagenesis kit (Agilent Technologies) according to manufacturer's instructions in order to test whether the predicted residues, which were identified in Example 9, affected the substrate specificity of acyl-ACP TEs. The residues of CvFatB2 were mutated to the corresponding residues in CvFatB1 with the exception of residues valine 110 (V110) and isoleucine 184 (I184), which were mutated to the bulkier residue, phenylalanine. The point mutations were introduced sequentially for the mutants that harbored multiple amino acid changes. All mutants were confirmed by sequencing. The results are shown in
This example describes the production of fatty acids in vivo by TE variants.
TE variants were analyzed in accordance with the method of Example 3. The results are shown in
Thus, in view of the above, the present invention provides the following:
A. A method of increasing production of fatty acids in a host cell or organism, which method comprises introducing into the host cell or organism and expressing therein a nucleic acid molecule comprising a nucleotide sequence encoding an acyl-acyl carrier protein (ACP) thioesterase (TE) from Bryantella formatexigens, whereupon the production of fatty acids in the host cell or organism is increased.
B. The method of A, wherein the host cell or organism is a bacterium, a yeast, an alga, or a crop plant.
C. A method of increasing production of short-chain fatty acids in a host cell or organism, which method comprises introducing into the host cell or organism and expressing therein a nucleic acid molecule comprising a nucleotide sequence encoding a mutant acyl-ACP TE derived from wild-type Bryantella formatexigens acyl-ACP TE, whereupon the production of short-chain fatty acids in the host cell or organism is increased and wherein the mutant acyl-ACP TE produces more short-chain fatty acids in the host cell or organism than the corresponding wild-type acyl-ACP TE.
D. The method of C, wherein the mutant acyl-ACP TE differs from wild-type Bryantella formatexigens acyl-ACP TE by two or more amino acid mutations comprising N169Y and S222I and wherein the mutant acyl-ACP TE has increased thioesterase activity compared to wild-type Bryantella formatexigens acyl-ACP TE.
E. The method of C, wherein the host cell or organism is a bacterium, a yeast, an alga, or a crop plant.
F. The method of D, wherein the host cell or organism is a bacterium, a yeast, an alga, or a crop plant.
G. A method of making a mutant Bryantella formatexigens acyl-ACP TE, which method comprises making a mutant Bryantella formatexigens acyl-ACP TE comprising two or more amino acid mutations comprising N169Y and S222I, whereupon a mutant Bryantella formatexigens acyl-ACP TE is made.
H. The method of G, wherein the mutant Bryantella formatexigens acyl-ACP TE has increased thioesterase activity compared to a corresponding wild-type Bryantella formatexigens acyl-ACP TE.
I. An isolated or purified nucleic acid molecule comprising a nucleotide sequence encoding a mutant acyl-ACP TE, which is derived from wild-type Bryantella formatexigens acyl-ACP TE, comprises two or more amino acid mutations comprising N169Y and S222I, and has increased thioesterase activity compared to wild-type Bryantella formatexigens acyl-ACP TE, wherein the isolated or purified nucleic acid molecule can be a vector.
J. A host cell or organism comprising the isolated or purified nucleic acid molecule of I.
K. The host cell or organism of J, wherein the host cell or organism is a bacterium, a yeast, an alga, or a crop plant.
L. An isolated or purified mutant acyl-ACP TE, which is derived from wild-type Bryantella formatexigens acyl-ACP TE, comprises two or more amino acid mutations comprising N169Y and S222I, and has increased thioesterase activity compared to wild-type Bryantella formatexigens acyl-ACP TE.
M. A method of making a chimeric Cuphea viscosissima acyl-ACP TE, which method comprises replacing a segment of a wild-type Cuphea viscosissima acyl-ACP
TE with a segment of another acyl-ACP TE, whereupon a chimeric Cuphea viscosissima acyl-ACP TE is made.
N. The method of M, wherein the segment of another acyl-ACP TE gene is a segment of another Cuphea viscosissima acyl-ACP TE.
O. The method of M, which method comprises replacing a segment of a wild-type Cuphea viscosissima FatB1 (CvFatB1) gene with a segment of another acyl-ACP TE gene to produce a chimeric CvFatB1 gene or replacing a segment of a wild-type Cuphea viscosissima FatB2 (CvFatB2) gene with a segment of another acyl-ACP TE gene to produce a chimeric CvFatB2 gene.
P. The method of 0, which method comprises replacing a segment of a wild-type CvFatB1 gene with a segment of a CvFatB2 gene to produce a chimeric CvFatB1 gene or replacing a segment of a wild-type CvFatB2 gene with a segment of a CvFatB1 gene to produce a chimeric CvFatB2 gene.
Q. The method of M, wherein the chimeric Cuphea viscosissima acyl-ACP TE (i) has a substrate specificity that differs from the corresponding wild-type Cuphea viscosissima acyl-ACP TE, (ii) produces a total amount of fatty acids that differs from the total amount of fatty acids produced by the corresponding wild-type Cuphea viscosissima acyl-ACP TE, or (iii) has a substrate specificity and produces a level of a fatty acid, both of which differ from the corresponding wild-type Cuphea viscosissima acyl-ACP TE.
R. An isolated or purified nucleic acid molecule comprising a nucleotide sequence encoding a chimeric Cuphea viscosissima acyl-ACP TE gene, which comprises a segment of another acyl-ACP TE gene, wherein the isolated or purified nucleic acid molecule can be a vector.
S. The isolated or purified nucleic acid molecule of R, wherein the segment of another acyl-ACP TE gene is a segment of another Cuphea viscosissima acyl-ACP TE gene.
T. The isolated or purified nucleic acid molecule of R, wherein the chimeric Cuphea viscosissima acyl-ACP TE gene is a chimeric FatB1 gene or a chimeric FatB2 gene.
U. The isolated or purified nucleic acid molecule of T, wherein the chimeric Cuphea viscosissima acyl-ACP TE gene is a chimeric FatB1 gene comprising a segment of a Cuphea viscosissima FatB2 gene or the chimeric Cuphea viscosissima acyl-ACP TE gene is a chimeric FatB2 gene comprising a segment of a Cuphea viscosissima FatB1 gene.
V. A host cell or organism comprising the isolated or purified nucleic acid molecule of R—U.
W. An isolated or purified chimeric Cuphea viscosissima acyl-ACP TE, which comprises a segment of another acyl-ACP TE.
X. The isolated or purified chimeric Cuphea viscosissima acyl-ACP TE of W, wherein the segment of another acyl-ACP TE is a segment of another Cuphea viscosissima acyl-ACP TE.
Y. The isolated or purified chimeric Cuphea viscosissima acyl-ACP TE of W, which is a chimera of the TE encoded by a FatB1 gene or a chimera of the TE encoded by a FatB2 gene.
Z. The isolated or purified chimeric Cuphea viscosissima acyl-ACP TE of Y, which is a chimera of the TE encoded by a FatB1 gene comprising a segment of the TE encoded by a FatB2 gene or a chimera of the TE encoded by a FatB2 gene comprising a segment of the TE encoded by a FatB1 gene.
AA. A method of altering the specificity of a plant acyl-ACP TE for at least one of its substrates, which method comprises introducing into the plant acyl-ACP TE a substrate specificity-altering mutation in the region corresponding to amino acids 118-167 of the mature amino acid sequence of the Cuphea viscosissima acyl-ACP TE encoded by FatB2, whereupon the specificity of the plant acyl-ACP TE for at least one of its substrates is altered.
AB. The method of AA, which comprises mutating at least one amino acid corresponding to an amino acid selected from the group consisting of amino acid 133, amino acid 142, and amino acid 143 of the mature amino acid sequence of the Cuphea viscosissima acyl-ACP TE encoded by FatB2.
AC. The method of AB, which further comprises mutating at least one amino acid corresponding to an amino acid selected from the group consisting of amino acid 110 and amino acid 184 of the mature amino acid sequence of the Cuphea viscosissima acyl-ACP TE encoded by FatB2.
AD. The method of AA, which further comprises altering the level of activity of the plant acyl-ACP TE by a method comprising mutating at least one amino acid corresponding to an amino acid selected from the group consisting of amino acid 173, amino acid 176, and amino acid 205 of the mature amino acid sequence of the Cuphea viscosissima acyl-ACP TE encoded by FatB2, whereupon the level of activity of the plant acyl-ACP TE is altered.
AE. The method of AB, which further comprises altering the level of activity of the plant acyl-ACP TE by a method comprising mutating at least one amino acid corresponding to an amino acid selected from the group consisting of amino acid 173, amino acid 176, and amino acid 205 of the mature amino acid sequence of the Cuphea viscosissima acyl-ACP TE encoded by FatB2, whereupon the level of activity of the plant acyl-ACP TE is altered.
AF. The method of AC, which further comprises altering the level of activity of the plant acyl-ACP TE by a method comprising mutating at least one amino acid corresponding to an amino acid selected from the group consisting of amino acid 173, amino acid 176, and amino acid 205 of the mature amino acid sequence of the Cuphea viscosissima acyl-ACP TE encoded by FatB2, whereupon the level of activity of the plant acyl-ACP TE is altered.
AG. A method of altering the level of activity of a plant acyl-ACP TE, which method comprises mutating at least one amino acid corresponding to an amino acid selected from the group consisting of amino acid 173, amino acid 176, and amino acid 205 of the mature amino acid sequence of the Cuphea viscosissima acyl-ACP TE encoded by FatB2, whereupon the level of activity of the plant acyl-ACP TE is altered.
AH. The method of AG, which further comprises altering the specificity of the plant acyl-ACP TE for at least one of its substrates by a method comprising introducing into the plant acyl-ACP TE a substrate specificity-altering mutation in the region corresponding to amino acids 118-167 of the mature amino acid sequence of the Cuphea viscosissima acyl-ACP TE encoded by FatB2, whereupon the specificity of the plant acyl-ACP TE for at least one of its substrates is altered.
AI. The method of AH, which comprises mutating at least one amino acid selected from the group consisting of amino acid 133, amino acid 142, and amino acid 143 of the mature amino acid sequence of the Cuphea viscosissima acyl-ACP TE encoded by FatB2.
AJ. The method of AI, which further comprises mutating at least one amino acid corresponding to an amino acid selected from the group consisting of amino acid 110 and amino acid 184 of the mature amino acid sequence of the Cuphea viscosissima acyl-ACP TE encoded by FatB2.
AK. An isolated or purified nucleic acid molecule comprising a nucleotide sequence encoding a mutant plant acyl-ACP TE, which comprises a substrate specificity-altering mutation in the region corresponding to amino acids 118-167 of the mature amino acid sequence of the Cuphea viscosissima acyl-ACP TE encoded by FatB2, wherein the isolated or purified nucleic acid molecule can be a vector.
AL. The isolated or purified nucleic acid molecule of AK, wherein the mutant plant acyl-ACP TE comprises a mutation of at least one amino acid corresponding to an amino acid selected from the group consisting of amino acid 133, amino acid 142, and amino acid 143 of the mature amino acid sequence of the Cuphea viscosissima acyl-ACP TE encoded by FatB2.
AM. The isolated or purified nucleic acid molecule of AL, wherein the mutant plant acyl-ACP TE further comprises a mutation of at least one amino acid corresponding to an amino acid selected from the group consisting of amino acid 110 and amino acid 184 of the mature amino acid sequence of the Cuphea viscosissima acyl-ACP TE encoded by FatB2.
AN. The isolated or purified nucleic acid molecule of AK-AM, wherein the mutant plant acyl-ACP TE further comprises a level of activity-altering mutation of at least one amino acid corresponding to an amino acid selected from the group consisting of amino acid 173, amino acid 176, and amino acid 205 of the mature amino acid sequence of the Cuphea viscosissima acyl-ACP TE encoded by FatB2.
AO. An isolated or purified nucleic acid molecule comprising a nucleotide sequence encoding a mutant plant acyl-ACP TE, which comprises a level of activity-altering mutation of at least one amino acid corresponding to an amino acid selected from the group consisting of amino acid 173, amino acid 176, and amino acid 205 of the mature amino acid sequence of the Cuphea viscosissima acyl-ACP TE encoded by FatB2, wherein the isolated or purified nucleic acid molecule can be a vector.
AP. The isolated or purified nucleic acid molecule of AO, wherein the mutant plant acyl-ACP TE further comprises a substrate specificity-altering mutation in the region corresponding to amino acids 118-167 of the mature amino acid of the Cuphea viscosissima acyl-ACP TE encoded by FatB2.
AQ. The isolated or purified nucleic acid molecule of AP, wherein the mutant plant acyl-ACP TE comprises a mutation of at least one amino acid corresponding to an amino acid selected from the group consisting of amino acid 133, amino acid 142, and amino acid 143 of the mature amino acid sequence of the Cuphea viscosissima acyl-ACP TE encoded by FatB2.
AR. The isolated or purified nucleic acid molecule of AQ, wherein the mutant plant acyl-ACP TE further comprises a substrate specificity-altering mutation of at least one amino acid corresponding to an amino acid selected from the group consisting of amino acid 110 and amino acid 184 of the mature amino acid sequence of the Cuphea viscosissima acyl-ACP TE encoded by FatB2.
AS. A host cell or organism comprising the isolated or purified nucleic acid molecule of AK-AR.
AT. An isolated or purified mutant plant acyl-ACP TE, which comprises a substrate specificity-altering mutation in the region corresponding to amino acids 118-167 of the mature amino acid sequence of the Cuphea viscosissima acyl-ACP TE encoded by FatB2.
AU. The isolated or purified mutant plant acyl-ACP TE of AT, which comprises a mutation of at least one amino acid corresponding to an amino acid selected from the group consisting of amino acid 133, amino acid 142, and amino acid 143 of the mature amino acid sequence of the Cuphea viscosissima acyl-ACP TE encoded by FatB2.
AV. The isolated or purified mutant plant acyl-ACP TE of AU, which further comprises a substrate specificity-altering mutation of at least one amino acid corresponding to an amino acid selected from the group consisting of amino acid 110 and amino acid 184 of the mature amino acid sequence of the Cuphea viscosissima acyl-ACP TE encoded by FatB2.
AW. The isolated or purified mutant plant acyl-ACP TE of AT-AV, which further comprises a level of activity-altering mutation of at least one amino acid corresponding to an amino acid selected from the group consisting of amino acid 173, amino acid 176, and amino acid 205 of the mature amino acid sequence of the Cuphea viscosissima acyl-ACP TE encoded by FatB2.
AX. An isolated or purified mutant plant acyl-ACP TE, which comprises a level of activity-altering mutation of at least one amino acid corresponding to an amino acid selected from the group consisting of amino acid 173, amino acid 176, and amino acid 205 of the mature amino acid sequence of the Cuphea viscosissima acyl-ACP TE encoded by FatB2.
AY. The isolated or purified mutant plant acyl-ACP TE of claim AX, which further comprises a substrate specificity-altering mutation in the region corresponding to amino acids 118-167 of the mature amino acid of the Cuphea viscosissima acyl-ACP TE encoded by FatB2.
AZ. The isolated or purified mutant plant acyl-ACP TE of claim AY, which comprises a mutation of at least one amino acid corresponding to an amino acid selected from the group consisting of amino acid 133, amino acid 142, and amino acid 143 of the mature amino acid sequence of the Cuphea viscosissima acyl-ACP TE encoded by FatB2.
BA. The isolated or purified mutant plant acyl-ACP TE of claim AZ, which further comprises a substrate specificity-altering mutation of at least one amino acid corresponding to an amino acid selected from the group consisting of amino acid 110 and amino acid 184 of the mature amino acid sequence of the Cuphea viscosissima acyl-ACP TE encoded by FatB2.
All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.
The use of the terms “a,” “an,” “the,” and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to illuminate better the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.
Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. It should be understood that the illustrated embodiments are exemplary only, and should not be taken as limiting the scope of the invention. All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.
Claims
1. A method of increasing production of short-chain fatty acids in a host cell or organism, which method comprises introducing into the host cell or organism and expressing therein a nucleic acid molecule comprising a nucleotide sequence encoding an acyl-acyl carrier protein (ACP) thioesterase (TE) from either wild-type Bryantella formatexigens having the amino acid sequence of SEQ ID NO:24 or a mutant acyl-ACP TE derived therefrom, whereupon the production of fatty acids in the host cell or organism is increased.
2. The method of claim 1, wherein the host cell or organism is a bacterium, a yeast, an alga, or a crop plant.
3. The method of claim 2, wherein the bacterium is E. coli.
4. A method of making a mutant Bryantella formatexigens acyl-ACP TE, which method comprises making a mutant Bryantella formatexigens acyl-ACP TE, which is derived from wild-type Bryantella formatexigens acyl-ACP TE having the amino acid sequence of SEQ ID NO:24 and comprises two or more amino acid mutations comprising N169Y and S222I, whereupon a mutant Bryantella formatexigens acyl-ACP TE is made.
5. An isolated or purified nucleic acid molecule comprising a nucleotide sequence encoding a mutant acyl-ACP TE, which is derived from wild-type Bryantella formatexigens acyl-ACP TE having the amino acid sequence of SEQ ID NO:24, comprises two amino acid mutations comprising N169Y and S222I, and has increased thioesterase activity compared to wild-type Bryantella formatexigens acyl-ACP TE, wherein the isolated or purified nucleic acid molecule can be a vector.
6. A host cell or organism comprising the isolated or purified nucleic acid molecule of claim 5.
7. The host cell or organism of claim 6, wherein the host cell or organism is a bacterium, a yeast, an alga, or a crop plant.
8. The host cell or organism of claim 7, wherein the bacterium is E. coli.
9. An isolated or purified mutant acyl-ACP TE, which is derived from wild-type Bryantella formatexigens acyl-ACP TE, comprises two amino acid mutations comprising N169Y and S222I, and has increased thioesterase activity compared to wild-type Bryantella formatexigens acyl-ACP TE.
Type: Application
Filed: Jan 18, 2015
Publication Date: Nov 12, 2015
Inventors: Basil J. Nikolau (Ames, IA), Marna Yandeau-Nelson (Ames, IA), Fuyuan Jing (Ames, IA)
Application Number: 14/599,528
