High-throughput expression of fusion proteins

The expression of putative ORFs as fusion proteins can accelerate research greatly. The availability of an epitope tag allows the use of Western blotting as an efficient means to identify useful recombinant plasmids, which can then be used to study protein function. In addition, the epitope tag can be extremely useful in downstream applications such as protein purification, immunolocalization, and immunoprecipitation experiments. The preceding protocols should be applicable to a variety of expression vectors, and should be useful in the identification of functional plasmids. The protocols require no exotic equipment and can be adapted for use in high-throughput transfection assays, protein purification protocols, and immunolocalization studies.

Small molecule-based chemical affinity system for the purification of proteins

A new chemical affinity system is described for the purification of proteins. The Linx Affinity Purification System enables researchers to quickly and easily bind a protein ligand to a chromatographic matrix and use the resulting affinity resin to purify a second protein from crude mixtures. The entire process takes approximately 2 h.

Production of a recombinant bovine enterokinase catalytic subunit in the methylotrophic yeast Pichia pastoris

We describe the heterologous expression of a 26.3 kD protein containing the catalytic domain of bovine enterokinase (EKL) in the methylotrophic yeast Pichia pastoris. A highly active protein is secreted and glycosylated, and it has the native amino-terminus of EKL. The cDNA encoding EKL was cloned with the KEX2 protease cleavage site following the alpha mating factor prepro secretion signal from Saccharomyces cerevisiae. The secreted EKL was easily purified from the few native proteins found in the P. pastoris fermentation supernatant, using ion exchange and affinity chromatography. The yield of the purified EKL was 6.3 mg per liter of fermentation culture. This is significantly higher than previous reports of expressions in E. coli and COS cells. The ability of this highly specific protease to cleave immediately after the carboxyl-terminal residue of the (Asp)4-Lys recognition sequence allows regeneration of native amino-terminal residues of recombinant proteins. Its application is demonstrated by the removal of thioredoxin (TrxA), and polyhistidine fusion partners from proteins of interest.