Insulin production methods and pro-insulin constructs

Abstract

Novel pro-insulin having specific amino acid and/or nucleic acid modifications suitable for improved methods of insulin production are provided. Novel and highly efficient processes for preparing the pro-insulin preparations and preparations containing them are also disclosed. The novel pro-insulin preparations may be converted into human insulin useful in therapeutic preparations. Novel peptides of the C-peptide, and N terminus, including RREAEALQVGQVELGGGPGAGSLQPLALEGSLQAR (SEQ ID NO:32), and MHHHHHHGGR (SEQ ID NO:36) respectively are provided, as well as the unique nucleic acid molecules encoding them.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent application Ser. No. 11/725,731, filed Mar. 20, 2007, which claims priority to and the benefit of U.S. Provisional Patent Application Ser. No. 60/874,655, filed Dec. 13, 2006. The entire disclosure and contents of these documents are hereby incorporated by reference.

BACKGROUND

1. Field of the Invention

The present invention in a general and overall sense relates to the field of recombinant proteins and peptides. The invention also relates to the field of molecular processes and methods for producing recombinant proteins particularly methods that employ E. coli as an expression vehicle. The invention also relates to compositions and methods for preparing pro-insulin, insulin, and both of these alone or in combination with each other and with other compositions.

2. Background of the Related Art

Insulin is a polypeptide hormone secreted by beta-cells of the pancreas. This hormone is made up of two polypeptide chains, an A-chain of 21 amino acids, and a B-chain of 30 amino acids. These two chains are linked to one another in the mature form of the hormone by two interchain disulfide bridges. The A-chain also features one intra-chain disulfide bridge.

Insulin is a hormone that is synthesized in the body in the form of a single-chain precursor molecule, pro-insulin. Pro-insulin is a molecule comprised of a prepeptide of 24 amino acids, followed by the B-chain peptide, a C-peptide of 35 amino acids, and an A-chain peptide. The C-peptide of this precursor insulin molecule contains the two amino acids, lysine-arginine (LR) at its carboxy end (where it attaches to the A-chain), and the two amino acids, arginine-arginine (RR) at its amino end (where it attaches to the B-chain). In the mature insulin molecule, the C-peptide is cleaved away from the peptide so as to leave the A-chain and the B-chain connected directly to one another in its active form.

Molecular biology techniques have been used to produce human pro-insulin. In this regard, three major methods have been used for the production of this molecule. Two of these methods involve Escherichia coli, with either the expression of a large fusion protein in the cytoplasm (Chance et al. (1981), and Frank et al. (1981) in Peptides: Proceedings of the 7^th American Peptide Chemistry Symposium (Rich, D. and Gross, E., eds.), pp. 721-728, 729-739, respectively, Pierce Chemical Company, Rockford, Ill.), or the use of a signal peptide to enable secretion into the periplasmic space (Chan et al. (1981) P.N.A.S., U.S.A., 78:5401-5404). A third method utilizes yeast, especially Saccharomyces cerevisiae, to secrete the insulin precursor into the medium (Thim, et al. (1986), P.N.A.S., U.S.A., 83: 6766-6770).

Chance et al. report a process for preparing insulin by producing each of the A and B chains of insulin in the form of a fusion protein by culturing E. coli that carries a vector compromising a DNA encoding the fusion protein, cleaving the fusion protein with cyanogen bromide to obtain the A and the B chains, sulfonating the A and B chains to obtain sulfonated chains, reacting the sulfonated B chain with an excess amount of the sulfonated A chain; and then purifying the resultant products to obtain insulin. Drawbacks associated with this process are that it requires two fermentation processes and the requirement of a reaction step for preparing the sulfonated A chain and the sulfonated B chain. This results in a low insulin yield.

Frank et al. described a process for preparing insulin in the form of a fusion protein in E. coli. In this process, pro-insulin is produced in the form of a fusion protein by culturing E. coli which carries a vector comprising a nucleic acid sequence (DNA) encoding for the fusion protein, cutting the fusion protein with cyanogens bromide to obtain pro-insulin, sulfonating the pro-insulin and separation of the sulfonated pro-insulin, refolding the sulfonated pro-insulin to form correct disulfide bonds, treating the refolded pro-insulin with trypsin and carboxypeptidase B, and then purifying the resultant product to obtain insulin. However, the yield of the refolded pro-insulin having correctly folded disulfide bonds is reported to sharply decrease as the concentration of the pro-insulin increases. This is allegedly due to, at least among other reasons, misfolding of the protein, and some degree of polymerization being involved. Hence, the process entails the inconvenience of using laborious purification steps during the recovery of pro-insulin.

Thim et al. report a process for producing insulin in yeast, Saccharomyces cerevisiae. This process has the steps of producing a single chain insulin analog having a certain amino acid sequence by culturing Saccharomyces cerevisiae cells, and isolating insulin therefrom through the steps of: purification, enzyme reaction, acid hydrolysis and a second purification. This process, however, results in an unacceptably low yield of insulin.

The role of the native C-peptide in the folding of pro-insulin is not precisely known. The dibasic terminal amino acid sequence at both ends of the C-peptide sequence has been considered necessary to preserve the proper processing and/or folding of the pro-insulin molecule to insulin.

Other amino acids within the C-peptide sequence, however, have been modified with some success. For example, Chang et al. (1998) (Biochem. J., 329:631-635) described a shortened C-peptide of a five (5) amino acid length, -YPGDV- (SEQ ID NO:1), that includes a preserved terminal di-basic amino acid sequence, RR at one terminal end, and LR at the other terminal end, of the peptide. Preservation of the dibasic amino acid residues at the B-chain-C peptide (B-C) and C-peptide-A-chain junctures is taught as being a minimal requirement for retaining the capacity for converting the pro-insulin molecule into a properly folded mature insulin protein. The production of the recombinant human insulin was described using E. coli with a shortened C-peptide having a dibasic amino acid terminal sequence.

One of the difficulties and/or inefficiencies associated with the production of recombinant insulin employing a pro-insulin construct having the conserved, terminal di-basic amino acid sequence in the C-peptide region is the presence of impurities, such as Arg-insulin, in the reaction mixture, once enzymatic cleavage to remove the C-peptide is performed. This occurs as a result of misdirected cleavage of the pro-insulin molecule so as to cleave the C-peptide sequence away from the A-chain at this juncture, by the action of trypsin. Trypsin is a typical serine protease, and hydrolyses a protein or peptide at the carboxyl terminal of an arginine or lysine residue (Enzymes, pp. 261-262 (1979), ed. Dixon, M. & Webb, E. C. Longman Group Ltd., London). This unwanted hydrolysis results in the unwanted ARG-AO-insulin by-product, and typically constitutes about 10% of the reaction yield. Hence, an additional purification step is required. The necessity of an additional purification step makes the process much more time consuming, and thus expensive, to use. Moreover, an additional loss of yield may be expected from the necessity of this additional purification step.

Others have described the use of pro-insulin constructs that do not have a conserved terminal dibasic amino acid sequence of the C-peptide region. For example, U.S. Pat. No. 6,777,207 (Kjeldsen et al.) relates to a novel pro-insulin peptide construct containing a shortened C-peptide that includes the two terminal amino acids, glycine-arginine or glycine-lysine at the carboxyl terminal end that connects to the A-chain of the peptide. The B-chain of the pro-insulin construct described therein has a length of 29 amino acids, in contrast to the native 30 amino acid length of the native B-chain in human insulin. The potential effects of this change to the native amino acid sequence of the B-chain in the human insulin produced are yet unknown. Methods of producing insulin using these pro-insulin constructs in yeast are also described. Inefficiencies associated with correct folding of the mature insulin molecule when yeast utilized as the expression host, render this process, among other things, inefficient and more expensive and time consuming to use. In addition, yeast provides a relatively low insulin yield, due to the intrinsically low expression levels of a yeast system as compared to E. coli.

As evidenced from the above review, a present need exists for a more efficient process for production of human insulin that is efficient, eliminates currently necessary purification steps, and that at the same time improves and/or preserves acceptable production yield requirements of the pharmaceutical industry.

The above references are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background.

SUMMARY OF THE INVENTION

The present invention provides novel pro-insulin compositions. These compositions may be further defined as comprising a peptide, an amino acid sequence, or a nucleic acid sequence encoding a modified C-peptide or a modified pro-insulin molecule, or a pharmaceutical preparation of these peptides in a pharmaceutically acceptable carrier solution and/or diluent. Among other distinguishing features, the novel pro-insulin as disclosed herein includes a unique non-di-basic amino acid sequence at one or both of its C-peptide terminal ends. In some embodiments, the constructs are described as an N-terminal multiple His-tagged pro-insulin construct. In particular embodiments, the N-terminal multiple His-tagged pro-insulin construct comprises a 6-histidine N-terminal tag (SEQ ID NO:24). In some embodiments, the construct comprises a structure as defined in Formula I or Formula II:

Formula I:
MHHHHHHGGR (SEQ ID NG:2)-X1-C peptide-X2,
or
Formula II:
MHHHHHHGGR (SEQ ID NG:2)-X1-modified C peptide-X2

wherein X1 comprises an insulin B Chain, and wherein X2 comprises an insulin A Chain. In the Formula II construct, the modified C peptide is defined as a sequence having a non-dibasic (such as AR) amino acid sequence at a terminal end of the modified C peptide component that is adjacent the X2 component (insulin A chain) and/or a modification (such as RA) located adjacent the X1 component (insulin B chain) in the construct as depicted in Formula II.

The invention in particular aspects may be further defined as providing a novel pro-insulin composition. This composition may be further defined as comprising a peptide, an amino acid sequence, or nucleic acid sequence encoding the pro-insulin. The purified and transformed pro-insulin comprises a pharmaceutical preparation formulated with a pharmaceutically acceptable carrier solution and/or diluent.

The invention also provides a novel process for producing highly purified insulin that is more efficient than current techniques. In particular aspects, the process employs bacteria, such as E. coli.

The process presents many advantages, among them the advantage of reducing and/or eliminating the presence of unwanted and contaminating cleavage by-products characteristic of conventional manufacturing processes for producing recombinant human insulin in E. coli. Previously undesirable by-products evident in yield mixtures using conventional methods of producing recombinant human insulin included, by way of example, the production of an unwanted cleavage product, ARG-AO-insulin. A highly efficient process for the production of recombinant human insulin is presented that reduces and/or eliminates the presence of this and other unwanted and undesirable cleavage by-products, and that further presents the advantages of eliminating several time consuming, expensive, purification steps. A process having fewer technician-assisted steps is thus devised, and illustrates the additional advantage of eliminating the degree of inconsistency and/or error associated with technician assisted steps in the manufacturing process.

In some embodiments, the preparations comprise a pharmaceutically acceptable preparation comprising recombinant human insulin and being essentially free of pro-insulin.

An object of the invention is to solve at least the above problems and/or disadvantages and to provide at least the advantages described hereinafter.

Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objects and advantages of the invention may be realized and attained as particularly pointed out in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in detail with reference to the following drawings in which like reference numerals refer to like elements wherein:

FIG. 1, according to one aspect of the invention, presents a gel showing expression of the full length His-tagged/K64A pro-insulin (10.5 KDa) protein. The gel is from the expression product produced from the E. coli, BL21 strain, transformed with the above mentioned genes.

FIG. 2, according to one aspect of the invention, presents an HPLC of recombinant IPT human insulin. The chromatograph demonstrates that the preparation is high in purity with almost non-existent levels of pro-insulin.

FVNQHLCGSHLVEALYLVCGERGFFYTPKTRREAEDLQVGQVELGGGPGA
GSLQPLALEGSLQKRGIVEQCCTSICSLYQLENYCN

N-Terminal 6-His tagged clone with tryptic cleavage sequence for removal: (Utilization of a Nickel chelating column for high purity in a single step)

(SEQ ID NO: 28)
MHHHHHHGGRFVNQHLCGSHLVEALYLVCGERGFFYTPKTRREAEDLQVG
QVELGGGPGAGSLQPLALEGSLQKRGIVEQCCTSICSLYQLENYCN

Site Directed Mutagenesis of Lysine 64 to Alanine: Prevention of incorrect cleavage following the lysine. No arg-insulin contaminant generated, resulting in an increased yield.

(SEQ ID NO: 29)
MHHHHHHGGRFVNQHLCGSHLVEALYLVCGERGFFYTPKTRREAEDLQVG
QVELGGGPGAGSLQPLALEGSLQARGIVEQCCTSICSLYQLENYCN

Example 9

Purification Method for Production of Lys/Pro Insulin

The present example demonstrates the utility of the present invention for providing a unique construct and purification scheme that significantly improves the purification method for the production of Lys/Pro Insulin.

Lys/Pro Insulin is characterized as a short acting insulin analog, which, when combined with am insulin pump, allows for better blood glucose stability without the risk of hyperglycemia.

Amino acid sequence of the unique construct as defined in example 8.

(SEQ ID NO: 30)
MHHHHHHGGRFVNQHLCGSHLVEALYLVCGERGFFYTPKTRREAEDLQVG
QVELGGGPGAGSLQPLALEGSLQARGIVEQCCTSICSLYQLENYCN

Lys/Pro insulin modification with residues 28 and 29 reversed in their order:

(SEQ ID NO: 31)
MHHHHHHGGRFVNQHLCGSHLVEALYLVCGERGFFYTKPTRREAEDLQVG
QVELGGGPGAGSLQPLALEGSLQARGIVEQCCTSICSLYQLENYCN

A general outline of one method, by way of example and not exclusion, to isolate and/or enrich recombinant Lys/Pro insulin from a composition that is not enriched for FIG. 3, according to some aspects of the invention, presents a biopotency study showing relative glucose curves for rabbits injected with saline (control), Humulin R (positive control), and Elona Biotechnologies human insulin (test sample).

FIG. 4, according to some aspects to the invention, presents a flow scheme for the purification of insulin and Lys-Pro insulin, using the purification methods described in examples 1 and 9.

FIGS. 5A and 5B, according to some aspects of the invention, presents a reverse phase chromatography analysis of chromatogram with (5A) and without (5B) sodium sulfate.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention provides novel pro-insulin constructs, C-peptides, and methods for using these in a process to provide high yields of mature recombinant human insulin. The pro-insulin constructs include a novel C-peptide that includes a non-dibasic terminal amino acid sequence at one end.

In particular embodiments, the non-dibasic alanine-arginine (AR) sequence at the carboxyl terminus of the C-chain. The C-terminus of the C-peptide connects to the A-chain of the pro-insulin molecule. Advantageously, the positioning of these particular terminal amino acids in the C-peptide provides for an improved method for producing recombinant human insulin, having fewer steps, improved yields of the recombinant human insulin protein and less contaminating byproducts.

As used in the description of the present invention, the term “connecting peptide” or “C-peptide” is meant the connecting moiety “C” of the B-C-A polypeptide sequence of a single chain pro-insulin molecule. Specifically, in the native human insulin chain, the C-peptide connects to position 30 of the B-chain and position 1 of the A-chain. In the present invention, the A-chain and the B-chain of the pro-insulin constructs retain their native sequences and lengths. The C-peptide constructs disclosed have been modified so as to include different terminal amino acids relative to native C-peptide.

As in native human pro-insulin, the C-peptide constructs of the present invention connect position 30 of the B-chain and position 1 of the A-chain. The single chain pro-insulin molecules of the invention will include three (3) correctly positioned, disulphide bridges, as is characteristic of the native human pro-insulin molecule. The amino acid sequence of the B-chain and the A-chain of the pro-insulin constructs, as well as the human insulin products produced by the methods described herein, will have the native amino acid sequence characteristic of native human insulin.

As used in the description of the present invention, the terms “insulin precursor” or “pro-insulin” are described as a single-chain polypeptide in which, by one or more subsequent chemical and/or enzymatic processes, may be converted into human insulin.

As used in the description of the present invention, the term “pro-insulin analog” is defined as a pro-insulin molecule having one or more mutations, substitutions, deletions, and or additions, of the A, B and/or C chains relative to the native human pro-insulin nucleic acid sequence. The pro-insulin analogs are preferably such wherein one or more of the naturally occurring nucleic acids have been substituted with another nucleic acid within a triplet encoding for a particular amino acid.

The term “a” as used in the description of the present invention is intended to mean “one or more”, and is used to define both the singular and plural forms of the item or items to which it references, or to a feature or characteristic to which it refers. The use of the singular or plural in the claims or specification is not intended to be limiting in any way and also includes the alternative form.

The term “about” is intended to be inclusive of and to encompass both an exact amount as well as an approximate amount or range of values or levels of the item, ingredient, element, activity, or other feature or characteristic to which it references. Generally, and in some embodiments, the term “about” is intended to reference a range of values relatively close to the specific numerical value specifically identified. For example, “about 3 grams to about 5 grams” is intended to encompass a measure of in or around a value of 3 grams, concentration values between 3 grams and 5 grams, concentration values in and around 5 grams, as well as concentration values that are exactly 3 grams and exactly 5 grams.

As used in the description of the present process, a high protein concentration of the pro-insulin or insulin product is defined as a protein yield concentration of at least about 3 grams/liter, or between about 3 grams to about 5 grams per liter. The expression yield to be expected may be defined as a protein/peptide yield that is sufficient to detect via polyacrylamide gel electrophoreses (PAGE).

The invention in a general and overall sense relates to an improved process for preparing a heterologous recombinant protein in a prokaryotic host cell. This process is characterized in that it employs a unique recombinant protein that provides a useful and efficiently processed pro-insulin peptide having a unique, modified C-peptide region, as well as a His tagged N-terminal sequence.

By heterologous protein is meant that said protein in said prokaryotic host cell is not native, i.e., it occurs as a protein in peculiar or foreign (i.e., not native to) the host prokaryotic cell.

“Recombinant” means produced or modified by molecular-biological methods.

As used in the description of the present invention, the term “heterologous recombinant protein” is defined as any protein known to the skilled person in the molecular biological arts, such as, for example, insulin, pro-insulin, C-peptide, and proteins containing these together with any other protein or peptide fragment.

Prokaryotic host cells may be any host cells known to the skilled artisan in the molecular biological arts, and by way of example, Escherichia coli. Such types of cells available form public collections and useful in the practice of the present invention include, by way of example, the Deutsche Sammlung von Mikrooganismen and Zellkulturen GmbH, raunschweig, Germany, e.g., E. coli Strain K12 JM107 (DSM 3950).

Proteins and peptides are chains of amino acids linked by peptide bonds, which in the case of proteins give a defined structure that is typically required for activity. Peptides are chains of amino acids which may or may not have activity or a defined structure.

Human Insulin Amino Acid sequence: The sequence of amino acids which make up the native insulin A and B chains is as follows:

(SEQ ID NO: 3)
FVNQHLCGSHLVEALYLVCGERGFFYTPKTGIVEQCCTSICSLYQLENY
CN

The following reference Table 1 provides the triplet codons corresponding to each of the various amino acids that are used in the description of the present invention. As will be understood by those of skill in the art, the amino acid that may be used in any particularly defined position as part of any of the peptide, protein, or constructs otherwise defined herein by reference to a particular nucleotide triplet base pair may be encoded by a number of different nucleotide triplets that function to encode the same amino acid. For example, where the amino acid of the sequence defined herein is alanine (Ala, or A), the triplet codon of nucleic acids that may encode for this amino acid are: GCT, GCC, GCA, or GCG. The following table illustrates this definition of variables at and substitutions as can be applied to all of the naturally occurring amino acids sequences of the disclosure.

TABLE 1

U

C

A

G

U

UUU

UCU

UAU

UGU

U

{close oversize brace}

Phe

{close oversize brace}

Tyr

Cys

UUC

UCC

UAC

UGG

C

UUA

UCA

{close oversize brace}

Ser

UAA

Stop

UGA

Stop

A

{close oversize brace}

Leu

UUG

UCG

UAG

Stop

UGG

Trp

G

C

CUU

CCU

CAU

CGU

U

{close oversize brace}

His

CUC

CCC

CAC

CGC

C

CUA

{close oversize brace}

Leu

CCA

{close oversize brace}

Pro

CAA

CGA

{close oversize brace}

Arg

A

{close oversize brace}

Gln

CUG

CCG

CAG

CGG

G

It should be understood that process steps within the following description of the method may be modified, changed and/or eliminated, depending on the particular preferences of the processor and/or the particular mechanical apparatus available to the processor, as well as the specific reagents and/or materials available and/or convenience and/or economics of use.

Example 1

General Materials and Methods

The present example describes some of the general techniques used in the preparation and purification of the human pro-insulin product and in the further processing of the pro-insulin into a human insulin product.

A general outline of one method, by way of example and not exclusion, to isolate and/or enrich recombinant insulin from a composition that is not enriched for recombinant insulin and/or includes pro-insulin can be described by the following series of steps:

1. Fermentation of E. coli transformed with the vector containing the human pro-insulin derivative-encoding amino acid sequence.

2. Lysis—Lyse the E. coli cells containing inclusion bodies enriched with the desired peptide, resuspended in a basic Tris/salt buffer, using a Niro Soavi homogenizer.

3. Inclusion Body Washing—Contaminant protein removal is then accomplished via two sequential washes with a Tris/Triton X-100 buffer, followed by two sequential washes with a Tris/Tween-20 buffer, and finally a single wash with a Tris/NaCl buffer.

4. Solubilization—Inclusion bodies are then solubilized in 8M urea containing reducing agents. Complete solubilization is achieved by adjusting the pH to 10.5 with NaOH.

5. Dilution refolding—The solubilized protein is then diluted into refolding buffer (5 mM CAPS, pH 10.5 at 4° C.) to a final concentration of 0.5 mg/ml. Allow the sample to refold for ≧48 hours at 2-10° C. Add an equal amount of oxidized glutathione to the initial amount of reducing agent used in the solubilization buffer, followed by 5M NaCl and 1M Phosphate additions, to final concentrations of 250 mM and 25 mM respectively. Adjust pH to 7.9 with 6M HCl.

6. IMAC Chromatography—Load the dilute pro-insulin derivative containing composition onto an IMAC column to a maximum capacity of ≦15 mg/ml of resin. Elute the pro-insulin via a 15CV gradient from 0-400 mM Imidizole. Using RP-HPLC for analysis, pool the appropriate fractions containing the Pro-Insulin peak of interest at the desired purity level.

7. Buffer exchange—To the pool, add EDTA to a final concentration of 10 mM. Exchange the buffer using a membrane with a suitable molecular weight cutoff (ex. 3000 Da). The final buffer should be at least 97% exchanged to a 20 mM Tris-C1, pH 8.0 at 2-10° C. A protein concentration of approximately 10 mg/ml is desirable. Just prior to tryptic digest, 1M Glycine stock (pH 9.3-9.7 cold) is added to a final concentration of 100 mM and the sample pH is adjusted to 9.7 (cold).

8. Initial Trypsin Enzymatic Transformation/Proteolysis—The buffer exchanged sample is digested with a 2000:1 mass ratio of protein to trypsin. Once complete, based on HPLC, the digest is then quenched by the addition of acetic acid to ≧700 mM, to a pH of approximately 3.5. HPLC of the digest should show about 54% R30 and DI-R(30&31) insulin analogs.

9. Reverse Phase Chromatography—The digested insulin is loaded onto a C18 column and eluted isocratically using a buffer of 23% acetonitrile, 200 mM Sodium Sulfate and 0.16% phosphoric acid. Alternatively, a C4 column may be used with a 22% acetonitrile, 200 mM Sodium sulfate and 0.16% phosphoric acid buffer.

10. Buffer Exchange—Exchange the buffer using a membrane with a suitable molecular weight cutoff (3000 Da). The final buffer should be at least 97% exchanged to 5 mM acetic acid. 1M Glycine stock (pH 9.3-9.7 cold) is then added to a final concentration of 100 mM, which shifts the pH of the sample to approximately 8.6. The pH is then adjusted to approximately 9.3 with NaOH, and the sample is concentrated to 8-12 mg/ml.

11. Carboxypeptidase B transformation—The buffer exchanged sample is digested with a 1:1000 ratio of protein to carboxypeptidase B. The digest is monitored by RP-HPLC to determine reaction completion.

12. Crystallization—To the carboxypeptidase B digested insulin, an equal volume of crystallization buffer (2.4M NaCl, 0.1M Citric acid, 6 mM Zinc Chloride) is added, pH adjusted to ˜6.3, and the sample is incubated at room temperature. Completion of crystallization is determined by UV analysis of the supernatant. Insulin crystals are harvested by centrifugation or filtration, washed with ethanol, and dried in vaccuo. When ready for use, the recombinant product will be solubilized and portioned into appropriate sized individually packaged units. For example, the insulin prepared according to the present invention may be prepared in 100 unit/ml vials.

Example 2

Process for Preparation of Human Pro-Insulin Derivative in a Modified ptrcHis 2A (Kan) Vector

The present example demonstrates one of the expression vectors that may be used in the preparation of an appropriate vector that may be used to transform an appropriate cell capable of expressing the human pro-insulin derivative. The specific vector described here is the ptrcHis2A vector. This ptrcHis2A vector was first modified before the human pro-insulin derivative-encoding nucleic acid sequence was inserted into the vector.

The ptrcHis2A vector may be purchased from a commercial vendor (e.g., Invitrogen). Such a vector will then be modified to include a Kanamycin resistance gene in the middle of the ampicillin resistance gene so as to negate the ampicillin resistance. Ampicillin resistance heightens the potential for allergic reactions to preparations made using vector constructs that include the ampicillin resistance gene. Therefore it is preferable to eliminate the ampicillin resistance in the constructs that are prepared and used.

Example 3

Construction of Purified Human Pro-Insulin Gene Segment for Insertion into Vector

The present example is presented to demonstrate an example of the steps of a process that may be used in the present invention for preparing the human pro-insulin derivative nucleic acid sequence, as well as for preparing the modified C-peptide construct disclosed herein. The nucleic acid segment isolated in the present example was used as the starting material for creating the various insertion nucleic acid sequences described in the following examples.

The nucleic acid sequence of ATCC deposited clone, MCG-12292, was identified by the present inventors to include a nucleic acid sequence that encoded the native human pro-insulin gene. The human pro-insulin gene sequence was isolated from the nucleic acid sequence of the ATCC deposited clone, MCG-12292, and employed as a starting material in the preparation of the various modified forms of human pro-insulin and pro-insulin derivatives having the mini-C-peptide sequence substitution as defined herein.

Human Pro-insulin Gene in ATCC Clone MGC-12292: (Nucleic acid Sequence of interest=nucleic acid sequence at positions 132-392 (Pro-Insulin) of the clone). The initial pDNR-LIB vector containing the nucleic acid sequence of interest was isolated/purified from the MCG-12292 clone using a QIAprep Spin Miniprep Kit.

The following nucleic acid sequence is a portion of the nucleic acid sequence of the ATCC Clone MCC-12292 that was identified and selected by the present inventors, and does not represent the entire nucleic acid sequence of the deposited clone.

(SEQ ID NO: 4)
1   agccctccag gacaggctgc atcagaagag gccatcaagc agatcactgt ccttctgcca
61  tggccctgtg gatgcgcctc ctgcccctgc tggcgc tgct ggccctctgg ggacctgacc
121 cagaggcagc ctttgtgaac caacacctgt gcggctcaca cctggtggaa gctctctacc
181 tagtgtgcgg ggaacgaggc ttcttctaca cacccaagac ccgccgggag gcagaggacc
241 tgcaggtggg gcaggtggag ctgggcgggg gccctggtgc aggcagcctg cagcccttgg
301 ccctggaggg gtccctgcag aagcgtggca ttgtggaaca atgctgtacc agcatctgct
361 ccctctacca gctggagaac tactgcaact agacgcagcc cgcaggcagc cccccacccg
421 ccgcctcctg caccgagaga gatggaataa agcccttgaa ccaacaaaaa aaaaaaaaaa
481 aaaaaaaaaa aaaaa

The following nucleic acid sequence is a portion of the nucleic acid sequence of the ATCC Clone MGC. The portion of the nucleic acid sequence that is bolded in the above sequence represents an amino acid fragment, which is not required in the final pro-insulin molecule. The underlined portion represents the sequence fragment of interest (nucleic acids 132-392 of SEQ ID NO:4). The sequence is as follows:

(SEQ ID NO: 5)
1   tttgtgaac caacacctgt gcggctcaca cctggtggaa gctctctacc tagtgtgcgg
60  gsaacgaggc ttcttctaca cacccaagac ccgccsggag gcagaggacc tgcaggtggg gcaggtggag
130 ctgggcgggg gccctggtgc aggcagcctg cagcccttgg ccctggaggg gtccctgcag aagcgtggca
200 ttgtggaaca atgctgtacc agcatctgct ccctctacca gctggagaac tactgcaact ag

With the use of PCR, the above sequence of interest (nucleic acids 132-393 of SEQ ID NO:4) was amplified with an additional leader sequence (atgcatcatcatcatcatcatgaaggtggccgc (SEQ ID NO:34)=new start codon, histidine tag, and tryptic cleavage sequence) and purified using a QIAprep PCR purification kit.

Translation: The amino acids below depict the original native sequence coded in the ATCC Clone MGC-12292.

(SEQ ID NO: 6)
MALWMRLLPLLALLALWGPDPAAAFVNQHLCGSHLVEALYLVCERGFFYT
PKTRREAEDLQVGQVELGGGPGAGSLQPLALEGSLQKRGIVEQCCTSICS
LYQLENYCN

The initial cloning step removed the bolded amino acid region above and replaced it with the new leader sequence in bold below. The “GGR” represents the tryptic cleavage site, which will be utilized in the tryptic transformation reaction to remove this new leader sequence.

(SEQ ID NO: 7)
MHHHHHHGGRFVNQHLCGSHLVEALYLVCERGFFYTPKTRREAEDLGVGG
VELGGGPGAGSLGPLALEGSLQKRGIVEQCCTSICSLYQLENYCN

The underlined amino acids represent the C-peptide region of the native human pro-insulin molecule.

Cloning Procedure

The initial cloning step into the pTrcHis2A(Kan) vector utilized the EcoR1 site for the C-terminal ligation position, and the Nco1 site, indirectly, for the N-terminal ligation. In order to use an Nco 1 site directly for an N-terminal ligation, the gene of interest must contain an amino acid residue at position 2, which is encoded by a codon that starts with a guanine nucleotide. As the construct of interest does not have the required amino acid at position two, a “blunt end” ligation reaction was utilized instead of a direct Nco1 “sticky end” ligation.

The sequence of the RBS site and the MCS of the ptrcHis2A(Kan) vector is as follows:

(SEQ ID NO: 8)
RBS             NcoI          MCS            EcoRI
3′ TAAGGAGGAATAAACCATGGATCCGAGCTCGAGATCTGCAGCTGGTACCATATGGGAATTC 5′
(SEQ ID NO: 35)
3′ TAAGGAGGAATAAACCATGGATCCGAGCTCGAGATCTGCAGCTGGTATATGGGAATTC 5′

Primer Design:

Forward Primer: The forward primer will introduce the new N-terminal Histidine Tag and tryptic cleavage site. The forward primer was ordered with a phosphorylated 5′ end, which is required for the blunt end ligation reaction.

(SEQ ID NO: 9)
5′ (Phosphorylated) catcatcatcatcatcat ggtggccgctt
tgtgaaccaacacctgtgcggctc 3′

Reverse Primer: The reverse primer will introduce the EcoR1 site into the C-terminus of the sequence. The EcoR1 site will be used to accommodate the insertion of the Pro-insulin sequence into the vector. The reverse primer sequence is as follows:

(SEQ ID NO: 10)
EcoRI
3′ gatggtcgacctcttgatgacgttgatc-cttaagg 5′

The new generated PCR product is as follows:

(SEQ ID NO: 11)
His Tag      GGR
5′-Phos-catcatcatcatcatcatg gtggccgctt tgtgaaccaa
cacctgtgcggctcacacct ggtggaagct ctctacctag
tgtgcgggga acgggcttc ttctacacacccaagacccg
ccgggaggca gaggacctgc aggtgggca ggtggagctg
ggcgggggccctggtgcagg cagcctgcag cccttggccc
tggaggggtc cctgcagaag cgtggcattgtggaacaatg
ctgtaccagc atctgctccc tctaccagct ggagaactac
tgcaactagtccttaagg3′
EcoR1

Following the PCR reaction, the insert DNA was purified using the QIAprep Spin Miniprep Kit from Quaigen. This purified insert DNA was used to create a pTrcHis2A(Kan) vector having this purified Pro-insulin gene sequence (See Example 4).

Example 4

Ligation Reaction for Cloning the N-Terminal Modified Pro-Insulin Gene into the Modified pTrcHis2A (Kan) Vector

The present example demonstrates the process by which the Pro-insulin gene was ligated into the modified pTrcHis2A(Kan) vector.

A 5′ blunt end and a 3′ EcoR1 ligation reaction were utilized to insert the Pro-insulin gene into the pTrcHis2A (Kan) vector.

The sequence at the MCS site of the pTrcHis2A(Kan) is as follows:

(SEQ ID NO: 12)
RBS Site         NcoI
5′ TAAGGAGGAATAAACCATGGATCCGAGCTCGAGATCTGCAGCTGGTACCATATATGGGAATTC 3′
EcoRI

Initial cut of the Vector with Nco1: 5′ TAAGGAGGAATAAAC 3′ (SEQ ID NO:13) Nco1 cut leaves a “CATG” 5′ overhang. 3′ ATTCCTCCTTATTTGCTAC 5′ (SEQ ID NO:14) 5′ TAAGGAGGAATAAACCATG 3′ (SEQ ID NO:15) T4 DNA polymerase fills in the opposing strand 3 ATTCCTCCTTATTTGGTAC 5′ (SEQ ID NO:16) leaving a blunt end.

Blunt End Reaction: The DNA was digested with Nco1 for 1 hour at 37° C. using 2 μg of DNA and 10 units of Nco1. Following the hour digestion, 2 units of T4 DNA polymerase were added to the reaction and incubated at 12° C. for 15 minutes. The blunt end reaction was then stopped by addition of EDTA to a concentration of 10 mM and heating to 75° C. for 20 minutes. The vector DNA was then purified using the QIAprep Spin Miniprep Kit from Qiagen.

Following purification, the other end of the MCS was cut with EcoR1:

5′ TAAGGAGGAATAAACCATG	(SEQ ID NO: 17)	AATTC 3′
3′ ATTCCTCCTTATTTGGTACTTAA	(SEQ ID NO: 18)	G 5′

Now that the vector was prepared, the insert was digested with EcoR1, leaving a blunt ended phosphorylated N-terminus and an EcoR1 sticky end on the C-terminus. Following the EcoR1 digestions, the vector and insert DNA were both purified using the QIAprep Spin MiniPrep Kit from Qiagen.

Once purified, the insert was ligated into the vector using a 4 to 1 molar ratio of insert to vector DNA at 12° C. overnight.

Transformation: One microliter of the ligation reaction was used to transform competent BL21 E coli cells, which were plated on LB-Kan agar plates and incubated overnight at 37° C. Several clones were picked and sent to IUPUI for DNA sequencing. Clones with the correct sequence were screened for expression. Good expression was verified in all clones.

Example 5

Site Directed Mutagenesis for the Conversion of Lysine 64 to Alanine in the C-Peptide Region of Human Pro-Insulin

A site directed mutagenesis PCR reaction was employed to convert the lysine at position 64 to alanine The constructed His-tagged-Gly-Gly-Arg Pro-insulin gene constructed in Example 4 was used as the template.

The creation of this amino acid mutation eliminates the possibility of generation Arg-AO-insulin during purification. Trypsin is an enzyme that has specific cleavage activity at the C-terminus of arginine residues, and to a lesser extent, towards the C-terminus of lysine residues. In the transformation reaction, it is required that the C-peptide, including the arginine at position 65, be removed along with the N-terminal sequence. If trypsin cleaves at the lysine in position 64, it will be unable to remove the arginine at position 65, due to the fact that it requires at least one residue on both sides of a cleavage site. What results is the production of an unwanted by-product, arg-A-0-insulin. This by-product constitutes a small loss in yield and generates an undesired contaminant.

By converting this lysine 65 into another uncharged amino acid, particularly alanine, the arg-AO-insulin product is not formed. This is because the trypsin no longer acts to cleave at this particular site of the pro-insulin sequence.

Site directed mutagenesis was used to convert the lysine at position 64 to alanine. The procedure was adapted from the protocol in the Stratagene Quick Change Site Directed Mutagenesis kit. The PCR reaction utilized pFU Turbo polymerase because of its high fidelity compared with Taq polymerase. Site directed mutagenesis involves the synthesis of the entire gene along with the vector (pTrcHis2A(Kan)). The insulin (Met-His-tagged-Gly-Gly-Arg)/)pTrcHis2A(Kan) clone synthesized above (Example 4) was used as the template for the PCR reaction.

PCR Primers Used:

Initial Sequence:

K64
5′ ccctggaggggtccctgcagaagcgtggcattgtggaacaatgctgtacc 3′ (SEQ ID NO: 19)
Forward Primer:
5′ ggggtccctgcaggcgcgtggcattgtg 3′ (SEQ ID NO: 20)
Reverse Primer:
3′ ccccagggacgtccgcgcaccgtaacac 5′ (SEQ ID NO: 21)

The 50 μl PCR reaction was treated with 20 units of Dpn1, and incubated at 37° C. for 1 hour to digest all methylated template DNA before transforming chemically competent BL21 cells.

Following transformation into BL21 cells, several clones were sequenced for gene verification. The clone that was isolated was: Met-His-taggedGly-Gly-Arg/Pro-insulin/K64A/pTrcHis2A(Kan).

The expression of this clone was very good.

Final Gene product (Met-His tagged/Gly-Gly-Arg/Pro-Insulin/K64A):

(SEQ ID NO: 22)
5′ ATGCATCATCATCATCATCATGGTGGCCGCTTTGTGAACCAACACCT
GTGCGGCTCACACCTGGTGGAAGCTCTCTACCTAGTGTGCGGGGAACGAG
GCTTCTTCTACACACCCAAGACCCGCCGGGAGGCAGAGGACCTGCAGGTG
GGGCAGGTGGAGCTGGGCGGGGGCCCTGGTGCAGGCAGCCTGCAGCCCTT
GGCCCTGGAGGGGTCTCTGCAGGCGCGTGGCATTGTGGAACAATGCTGTA
CCAGCATCTGCTCCCTCTACCAGCTGGAGAACTACTGCAACTAG 3′

Amino Acid Sequence of the His-tagged/Gly-Gly-Arg/K64A Pro-insulin:

(SEQ ID NO: 230
MHHHHHHGGRFVNQHLCGSHLVEALYLVCGERGFFYTPKTRREAEDLGVG
GVELGGGPGAGSLQPLALEGSLGARGIVEQCCISICSLYQLENYCN

In the nucleic acid and amino acid sequences above, the bold and underlined portions identify the connecting C-peptide sequence.

Example 6

Full Length Substituted Pro-Insulin Construct and Uses Thereof in Production of Human Insulin

With regards to the full length Pro-Insulin substitution construct of His-Tagged/K64A, three unique modifications are present to the original gene that simplify purification and increase yield.

• • 1) The N-terminal sequence was modified by the addition of a 6-Histadine tag, which could be used to simplify the purification via the use of a Nickel chelating column as an initial purification step following refolding.
  • 2) Following the 6-His tag sequence on the N-terminus, a well documented tryptic cleavage site was introduced in order to provide a simple means of removing the N terminal tag following the metal chelating chromatography step. The sequence introduced was “Glycine, Glycine, Arginine”, with cleavage after the arginine.
  • 3) The third modification was the conversion of an amino acid located at position 64 (original Pro-insulin) of the native sequence, which is a lysine residue that is converted to an alanine The modification prevents the formation of arg-AO-insulin during the tryptic cleavage transformation step, which increases the theoretical yield.

All data thus far supports the modifications. The initial chelating column step yields a Tagged-Pro-Insulin pool of approximately greater than or equal to about 92% purity. The tryptic transformation step yields a final insulin molecule with high digestion efficiency which demonstrates the effectiveness of the “gly, gly, arg” cleavage sequence for N-terminal removal and the lack of an Arg-A-0-insulin at position 65 demonstrate the advantage of the replacement at position 64.

The individual transformation reactions, rather then a single transformation reaction, allows for the efficient removal of the Desthreonine byproduct which is created by cleavage at the Lysine at position 29. This cleavage can be minimized in the native sequence by introducing nickel to the transformation reactions. However, the presence of the Histidine tag in the clone described herein, prevents this nickel protection of lysine 29. The separate transformation reactions allow for almost complete removal of the desthreonine byproduct, which is created when trypsin cleaves at the lysine at position 28, removing the threonine at position 29.

The final purification steps, including the Reverse phase Chromatography, carboxy peptidase B transformation reactions and crystallization, yields a highly pure insulin (≧99%) sample, which by HPLC reverse phase analysis shows essentially no Pro-insulin analogs or N-terminal fragments (See FIG. 2). As well, the desthreonine contaminant can essentially be completely removed.

Amino Acid Sequences

The natural pro-insulin amino acid sequence is as follows:

(SEQ ID NO: 25)
MALWMRLLPLLALLALWGPDPAAAFVNQHLCGSHLVEALYLVCGERGFFY
TPKTRREAEDLQVGQVELGGGPGAGSLQPLALEGSLQKRGIVEQCCTSIC
SLYQLENYCN

Replacement of initial sequence with Tag and cleavage site:

(SEQ ID NO: 26)
MHHHHHHGGRFVNQHLCGSHLVEALYLVCGERGFFYTPKTRREAEDLQVG
QVELGGGPGAGSLQPLALEGSLQKRGIVEQCCTSICSLYQLENYCN

Conversion of lysine 64 to alanine:

(SEQ ID NO: 27)
MHHHHHHGGRFVNQHLCGSHLVEALYLVCGERGFFYTPKTRREAEDLQVG
QVELGGGPGAGSLQPLALEGSLQARGIVEQCCTSICSLYQLENYCN

Example 7

Biopotency Study of the Full Length Substituted Pro-Insulin Construct

The final purified Insulin samples were tested in vivo on rabbits to compare the biopotency against Humulin R. As analytical studies give a simple picture of a biological molecule's relative state compared with a standard, it is imperative that a bioassay be used to determine that the purified molecule of interest carries the required biological activity.

In Vivo Biological Method

The biological assay was on the current accepted procedure outlined in the United States Pharmacopeia. Testing was conducted by MPI Research.

Test subjects included 30 male rabbits which were given injections on two separate days of either the control (saline), positive control (Humulin R), or test sample (IPT (Elona Biotechnologies) Human insulin), through subcutaneous injection.

Dosing levels consisted of 0.35 or 0.7 international units (IU), administered at a dose volume of 0.35 ml/dose. The control group received saline on both days 1 and 3 at a dose volume of 0.35 ml/dose.

Glucose monitoring was conducted prior to dosing and at 30, 60, 90, 150, and 240 minutes following dosing on both days. Results showed comparable biopotency of IPT human insulin with Humulin R (see FIG. 3).

Example 8

Pro-Insulin Constructs

The present example demonstrates the utility of the present invention for providing unique Pro-Insulin constructs that are particularly useful and efficient in the methods of insulin production described herein.

Native Pro-Insulin AA sequence: recombinant Lys/Pro insulin and/or includes pro-insulin can be described by the following series of steps:

1. Fermentation of E. coli transformed with the vector containing the human pro-insulin derivative-encoding amino acid sequence:

2. Lysis—Lyse the E. coli cells containing inclusion bodies enriched with the desired peptide, resuspended in a basic Tris/salt buffer, using a Niro Soavi homogenizer.

3. Inclusion Body Washing—Contaminant protein removal is then accomplished via two sequential washes with a Tris/Triton X-100 buffer, followed by two sequential washes with a Tris/Tween-20 buffer, and finally a single wash with a Tris/NaCl buffer.

4. Solubilization—Inclusion bodies are then solubilized in 8M urea containing reducing agents. Complete solubilization is achieved by adjusting the pH to 10.5 with NaOH.

5. Dilution refolding—The solubilized protein is then diluted into refolding buffer (5 mM CAPS, pH 10.5 at 4° C.) to a final concentration of 0.5 mg/ml. Allow the sample to refold for ≧48 hours at 2-10° C. Add an equal amount of oxidized glutathione to the initial amount of reducing agent used in the solubilization buffer, followed by 5M NaCl and 1M Phosphate additions, to final concentrations of 250 mM and 25 mM respectively. Adjust pH to 7.9 with 6M HCl.

6. IMAC Chromatography—Load the dilute pro-insulin derivative containing composition onto an IMAC column to a maximum capacity of ≦15 mg/ml of resin. Elute the pro-insulin via a 15CV gradient from 0-400 mM Imidizole. Using RP-HPLC for analysis, pool the appropriate fractions containing the Pro-Insulin peak of interest at the desired purity level.

7. Buffer exchange—To the pool, add EDTA to a final concentration of 10 mM. Exchange the buffer using a membrane with a suitable molecular weight cutoff (ex. 3000 Da). The final buffer should be at least 97% exchanged to a 20 mM Tris-C1, pH 8.0 at 2-10° C. A protein concentration of approximately 20-25 mg/ml is desirable.

8. Trypsin and Carboxypeptidase Enzymatic Transformation—The buffer exchanged sample is digested with a 2000:1 and 1000:1 mass ratio of protein to trypsin and protein to carboxypeptidase B respectively. Once complete, based on HPLC, the digest is then quenched by the addition of acetic acid to ≧700 Mm, to a pH of approximately 3.5. HPLC of the digest should show about 54% Humalog (Lys/Pro insulin).

9. Reverse Phase Chromatography—The digested Lys/Pro insulin is loaded onto a C18 column and eluted isocratically using a buffer of 23% acetonitrile, 200 mM Sodium Sulfate and 0.16% phosphoric acid. Alternatively, a C4 column may be used with a 22% acetonitrile, 200 mM Sodium sulfate and 0.16% phosphoric acid buffer.

10. Buffer Exchange—Exchange the buffer using a membrane with a suitable molecular weight cutoff (˜3000 Da). The final buffer should be at least 97% exchanged to 0.01N acid, and the sample is concentrated to 8-12 mg/ml.

11. Crystallization—To the Lys/Pro insulin. an equal volume of crystallization buffer (2.4M NaCl, 0.1M Citric acid, 6 mM Zinc Chloride) is added, pH adjusted to ˜6.3, and the sample is incubated at room temperature. Completion of crystallization is determined by UV analysis of the supernatant. Insulin crystals are harvested by centrifugation or filtration, washed with ethanol, and dried in vaccuo. When ready for use, the recombinant product will be solubilized and portioned into appropriate sized individually packaged units. For example, the insulin prepared according to the present invention may be prepared in 100 unit/ml vials.

The present example demonstrates several advantages that utilization of the Lys/pro insulin construct has over the original insulin sequence used in the purification scheme seen Example 1:

• • a. Step 7 does not require the Glycine addition and pH adjustment to 9.7, which decreases the chances of desamino formation, typically seen in the high or low pH ranges.
  • b. The separate digestion reaction found in steps 8 and 11 of Example 1 are combined into a single digestion reaction in Step 8 above, which is carried out at pH 8.0, which decreases the possibility of desamino formation.
  • c. The Lys/pro insulin construct prevents the formation of Desthreonine-insulin, which is created in the trypsin transformation reaction. It represents approximately a 6-10% yield loss, and can only be separated from the Arg and Di-Arg insulin species on the reverse phase step.

Example 10

Sodium Sulfate in Recovery Process for Insulin

The reverse phase chromatography step for purification of Di-Arg and Single-Arg insulin species following tryptic digestion and prior to carboxypeptidase B digestion involves one of two methods:

1. A shallow gradient elution from 23.5% to 25% acetonitrile in the presence of 200 mM sodium sulfate and 0.16% phosphate, over 15 column volumes.
2. An isocratic elution of 23.5% acetonitrile in the presence of 200 mM sodium sulfate and 0.16% phosphate, over approximately 15 column volumes.

The above methods are specific to a C 18 reverse phase system with a 15 μM particle size and 200-300 Å pore, but may be adapted to a C4 or C8 system by adjusting the acetonitrile concentrations. As well, the particle size may be varied to decrease back pressure.

A study of the above methods was conducted to look at the effects of sodium sulfate on the chromatography. It was found that the sodium sulfate when removed from the buffers resulted in a high yield loss. The material did not seem to stick to the column effectively, leading to some material crashing off at the column void volume. Sodium sulfate is required to increase mass transfer within the column. (See FIGS. 5A and 5B).

This study demonstrates the requirement of sodium sulfate in the reverse phase buffers. Although a more detailed study has not been conducted to determine the minimum required concentration, it is also understood that the flow rate during loading is a crucial parameter, since the slower the load, the better chance that there will be binding to the column before the void volume is through.

All of the compositions and methods disclosed and claimed herein can be made and expressed without undue experimentation in light of the present disclosure.

While the compositions and methods of this invention have been described in terms of preferred embodiments, it will be apparent to those of skill in the art that variations may be applied to the compositions, the methods, and in the steps and in the sequence of steps of the methods and processes described herein without departing from the concept, spirit and scope of the invention. More specifically, it will be apparent that certain agents which are both chemically and physiologically related may be substituted for the agents described herein while the same or similar results would be achieved. All such similar substitutions and modifications apparent to those skilled in the art are deemed to be within the spirit, scope and concept of the inventions disclosed herein by the appended claims. Accordingly, the exclusive rights sought to be patented are as described in the claims below.

BIBLIOGRAPHY

The following references are specifically incorporated in their entirety.

• 1. U.S. Pat. No. 6,777,207 B2—Kjeldsen et al. (2004).
• 2. U.S. Pat. No. 4,916,212—Markussen et al. (1990).
• 3. U.S. Pat. No. 5,962,267—Shin et al. (1999).
• 4. EP Patent No. 0 055 945—Goeddel et al. (1981).
• 5. Chance et al. (1981), Peptides: Proceedings of the 7^th American Peptide Chemistry Symposium, pp. 721-728 (Rich, D. and Gross, E. eds.).
• 6. Chan et al. (1981), P.N.A.S., U.S.A., 78:5401-5404.
• 7. Thim et al. (1986), P.N.A.S., U.S.A., 83: 6766-6770.
• 8. Frank et al. (1981), Peptides: Proceedings of the 7^th American Peptide Chemistry Symposium, pp. 729-739 (Rich, D. and Gross, E. eds.).
• 9. Chang et al. (1998), Bio hern J. 329: 63 1-635.

Claims

1. A nucleic acid sequence encoding a polypeptide comprising the sequence A-RREAEALQVGQVELGGGPGAGSLQPLALEGSLQAR (SEQ ID NO:32)-B, wherein said A chain and said B chain are native human insulin chains.

2. A nucleic acid sequence encoding the polypeptide RREAEALQVGQVELGGGPGAGSLQPLALEGSLQA (SEQ ID NG:32) R.

3. An expression vector comprising the nucleic acid sequence of claim 1.

4. The expression vector of claim 3, wherein the expression vector is Pro-insulin (His Tagged)/K64A/pTrcHis2A(Kan),His:tagged-Gly-Gly-Arg/Pro-insulin/(Kan).

5. A microorganism transformed with the vector of claim 4.

6. The microorganism of claim 5 further defined as an E. coli transformed with plasmid Pro-Insulin (His Tagged)/K64A/pTcHis2A(Kan) plasmid.

7. An amino acid sequence comprising RREAEALQVGQVELGGGPGAGSLQPLALEGSLQA (SEQ ID NG:32) R.

8. A composition enriched for a peptide encoded by the amino acid sequence of claim 7.

9. A process for preparing a composition enriched for an insulin analog employing a modified human pro-insulin peptide comprising:

(a) preparing an isolated nucleic acid sequence encoding native human pro-insulin;

(b) modifying said nucleic acid sequence by providing a molecular tag on said modified pro-insulin sequence so as to provide a histidine-tagged modified pro-insulin peptide;

(c) converting a lysine residue to an alanine residue at position 64 in a C-peptide region of said pro-insulin sequence to provide a modified pro-insulin derivative gene sequence;

(d) inserting the modified pro-insulin derivative gene sequence into a suitable vector to provide a vector comprising said modified pro-insulin derivative gene sequence;

(e) transfecting a culture of competent cells comprising E. coli cells with said vector to provide transformed E. coli cells;

(f) culturing the transformed E. coli cells under conditions suitable for expression of the modified pro-insulin derivative gene sequence;

(g) disrupting said population of transformed E. coli cells to provide a composition comprising inclusion bodies containing the modified human pro-insulin;

(h) solubilizing said composition to provide a composition comprising unfolded peptide;

(i) refolding said unfolded peptide to provide refolded human pro-insulin derivative peptide;

(j) passing said composition over a metal chelating column (Nickel chelate) to purify said composition and collecting a purified preparation of said refolded human pro-insulin derivative peptide;

(k) transforming the collected purified preparation of refolded human pro-insulin derivative peptide into Arg and Di-Arg peptide species by tryptic digestion;

(l) purifying said Arg and Di-Arg peptide species by passing said peptides through a reverse phase column; and

(m) transforming the purified Arg and Di-Arg peptide species into insulin by carboxypeptidase B digestion and harvesting an insulin analog.

10. The process of claim 9 wherein the E. coli is a BL21 production E. coli.

11. The process of claim 9 wherein the peptide is further defined as comprising an amino acid sequence encoding a substituted human pro-insulin derivative protein having an amino acid sequence comprising: (SEQ ID NO: 30) MHHHHHHGGRFVNQHLCGSHLVEALYLVCGERGFFYTPKTRREAEDLQVG QVELGGGPGAGSLQPLALEGSLQARGIVEGCCTSICSLYGLENYCN.

12. The process of claim 9 wherein the reverse phase chromatography column is further defined as comprising a silica based media with a C4, C8, or C18 bonded phase.

13. The process of claim 9 wherein the suitable vector is a pTrcHis2A (Kan) vector.

14. A pharmaceutical product comprising recombinant human insulin prepared by the process of claim 9.

15. A process for preparing a human pro-insulin derivative comprising a C-peptide RREAEDLQVGQVELGGGPGAGSLQPLALEGSLQAR (SEQ ID NO:33), said process comprising: RREAEDLQVGQVELGGGPGAGSLQPLALEGSLQA (SEQ ID NG:33) R;

(a) preparing a pro-insulin peptide having a C-peptide amino acid sequence

(b) modifying said peptide to include a met-histidine-Gly-Gly-Arg tag at the N-terminus of said peptide;

(c) incorporating said nucleic acid sequence into an appropriate vector to provide a transformed vector; (pTrcHis vector);

(d) transforming a population of competent cells comprising E. coli cells with said vector to provide transformed E. coli cells;

(e) selecting transformed E. coli cells that express a peptide comprising an amino acid sequence -RREAEDLQVGQVELGGGPGAGSLQPLALEGSLQAR (SEQ ID NO:33);

(f) culturing a composition of said selected transformed cells under conditions suitable for expression of the peptide having said amino acid sequence;

(g) solubilizing said composition comprising said cells; and

(h) purifying the human pro-insulin derivative from the culture.

16. The process of claim 15 further comprising the step:

(i) crystallizing the human pro-insulin derivative.

17. The process of claim 15 further comprising preparing human insulin from the human pro-insulin derivative by enzymatic hydrolysis.

18. The process of claim 15 wherein the E. coli is a BL21 production E. coli.

19. A composition prepared by the process of claim 17, wherein said composition is essentially free of human pro-insulin.