Expression, purification, and C-terminal amidation of recombinant human glucagon-like peptide-1

Human glucagon-like peptide-1 (hGLP-1) (7-36) amide, a gastrointestinal hormone with a pharmaceutical potential in treating type 2 diabetes mellitus, is composed of 30 amino acid residues as a mature protein. We report here the development of a method for high-level expression and purification of recombinant hGLP-1 (7-36) amide (rhGLP-1) through glutathione S-transferase (GST) fusion expression system. The cDNA of hGLP-1-Leu, the 31st-residue leucine-extended precursor peptide, was prepared by annealing and ligating of artificially synthetic oligonucleotide fragments, inserted into pBluescript SK (+/-) plasmid, and then cloned into pGEX-4T-3 GST fusion vector. The fusion protein GST-hGLP-1-Leu, expressed in Escherichia coli strain BL21 (DE3), was purified by affinity chromatography after high-level culture and sonication of bacteria. Following cleavage of GST-hGLP-1-Leu by cyanogen bromide, the recombinant hGLP-1-Leu was released from fusion protein, and purified using QAE Sepharose ion exchange and RP C(18) chromatography. After purification, the precursor hGLP-1-Leu was transacylated by carboxypeptidase Y, Arg-NH(2) as a nucleophile, to produce rhGLP-1. Electrospray ionization mass spectrometry showed the molecular weight was as expected. The biological activity of rhGLP-1 in a rat model demonstrated that plasma glucose concentrations were significantly lower and insulin concentrations higher after intraperitoneal injection of rhGLP-1 together with glucose compared with glucose alone (P < 0.001).