Expression, purification, and characterization of recombinant human serum albumin fusion protein with two human glucagon-like peptide-1 mutants in Pichia pastoris

Glucagon-like peptide-1 (GLP-1) is a 30-residue peptide hormone secreted by intestinal L-cells in response to nutrient ingestion. In the present study, overlapping PCR technology was employed to construct two GLP-1 mutants (GLP-1(A2G))2 and human albumin (HSA) genes in vitro without linker. The spliced gene, (GLP-1(A2G))2-HSA, was over expressed under the control of promoter AOX1 and Mat alpha signal peptide in Pichia pastoris. SDS-PAGE and Western blotting were applied to assay the recombinant fusion protein in the culture broth. The results demonstrated that the recombinant (GLP-1(A2G))2-HSA concentration in the broth could reach a level of 245.0 mg/L and the expressed fusion protein was capable of cross-reacting with anti-human GLP-1 and anti-human albumin antibody. The recombinant (GLP-1(A2G))2-HSA protein was purified by ultrafiltration, columns of Q-sepharose fast flow and Superdex 75 size-exclusion. The recombinant (GLP-1(A2G))2-HSA protein obtained could lower in vivo glucose concentration in blood and stimulate in vitro islet cell proliferation. In mouse model, the fusion protein was detectable in plasma even 308 h after a single subcutaneous dose of 1.25 mg/kg. The result showed that the terminal biological half-time of the protein was about 54.2 h which is 650-fold longer than that of GLP-1. The pharmacokinetic analysis of the protein suggests its promising application in clinical medicine.