Abstract: Expression vectors and methods of protein purification, which allow for selection of full length protein over truncated forms of the protein being purified, are disclosed. The methods express a target protein as a three domain fusion, represented by formula I:A-[Li]-B-[L2]-C, where A is a first purification tag domain, C is the second purification tag domain and B is the target protein domain. A, B and C are preferably covalently linked by linkers, L1 and L2 may be optional. The purification tags at the N and C termini are different. The purification tags at the N and C termini are different. Expression vectors including nucleic acid sequences which encode the fusion protein represented by formula I are also disclosed. The vectors are used with host expression systems such as insect, yeast, or mammalian cells to express the target protein, which is subsequently purified as a function of the different affinity tags.

Abstract: Methods for detecting His-tagged proteins using metal ion-chelating nitrilotriacetate (NTA) probes and polyacrylamide gel electrophoresis (PAGE) are disclosed. In one embodiment, the method includes using a metal ion-loaded NTA probe coupled to a UV-excitable fluorophore with visible emission and the presence of His-tagged proteins in the sample is determined by exposing the gel following PAGE, to a UV-light source with naked human eye or bench camera visualization. The metal ion-loaded NTA-containing chelator head can be coupled to a fluorophore that is not UV-excitable (i.e., with the majority of emission and excitation in the visible region of the electromagnetic spectrum. The method includes separating proteins in a sample using PAGE, contacting the gel following electrophoresis with a composition containing a metal ion-loaded NTA probe coupled to the fluorophore, to allow binding of the probe to the His-tagged proteins, and detecting the presence of the probe and therefore of the His-tagged proteins.

Abstract: Described are affinity purification system that includes a carrier/surface that is non-cellular, and sliding clamp (SC) protein, and methods for purifying proteins that bind to the SC. The SC is associated with the carrier/surface via covalent/non-covalent interactions. To attain control of coupling site, the SC can be mutated via site-directed mutagenesis to introduce an exogenous residue and, the exogenous internal residue is conjugated to the non-cellular surface through the linker. The SC can also be coupled to the carrier via non-covalent interactions such as the affinity interactions involved in ligand/binding partner complex formation. The SC-based affinity purification system are used in a purification column as bait proteins, to isolate SC binding partners or non SC-binding proteins engineered to contain a SC binding site prior to its purification.

Abstract: Potassium ion sensing aptamers are disclosed. These aptamers have high specificity towards the potassium ion. Ligand-sensing aptamers with a built-in reporter are also disclosed. The built-in reporter is incorporated into the sugar-phosphate backbone of the aptamers. The built-in reporter may be an environmentally sensitive fluorescence dye, internally coupled to the aptamers. The environmentally sensitive fluorescence dye can sense the conformation changes induced by binding of the aptamers to the target ligand and transduces the conformational changes to a fluorescence change.

Abstract: Expression vectors and methods of protein purification, which allow for selection of full length protein over truncated forms of the protein being purified, are disclosed. The methods express a target protein as a three domain fusion, represented by formula I: A-[L1]-B-[L2]-C, where A is a first purification tag domain, C is the second purification tag domain and B is the target protein domain. A, B and C are preferably covalently linked by linkers, L1 and L2 as shown in Formula I, however, L1 and L2 may be optional. The purification tags at the N and C termini are different. Expression vectors including nucleic acid sequences which encode the fusion protein represented by formula I are also disclosed. The vectors are used with host expression systems such as insect, yeast, or mammalian cells to express the target protein, which is subsequently purified as a function of the different affinity tags.

Abstract: Methods for detecting His-tagged proteins using metal ion-chelating nitrilotriacetate (NTA) probes and polyacrylamide gel electrophoresis (PAGE) are disclosed. In one embodiment, the method includes using a metal ion-loaded NTA probe coupled to a UV-excitable fluorophore with visible emission and the presence of His-tagged proteins in the sample is determined by exposing the gel following PAGE, to a UV-light source with naked human eye or bench camera visualization. The metal ion-loaded NTA-containing chelator head can be coupled to a fluorophore that is not UV-excitable (i.e., with the majority of emission and excitation in the visible region of the electromagnetic spectrum. The method includes separating proteins in a sample using PAGE, contacting the gel following electrophoresis with a composition containing a metal ion-loaded NTA probe coupled to the fluorophore, to allow binding of the probe to the His-tagged proteins, and detecting the presence of the probe and therefore of the His-tagged proteins.