Secretory Expression of Human Insulin in Methylotrophic Yeast Pichia pastoris

The porcine insulin precursor (PIP) gene and its derivative form sp-PIP gene, which had a nona-peptide (called spacer peptide, sp) added at the 5' terminus of PIP gene, were inserted into the plasmid pPIC9 of Pichia pastoris to obtain secretory plasmid pPIC9/PIP and pPIC9/sp-PIP, respectively. P.pastoris GS115 was transformed by pPIC9/PIP or pPIC9/sp-PIP and the high-copy strains, P39(-sp) and S51(+sp), were selected by dot-blotting. The expression levels of PIP and sp-PIP were 10 mg/L and 40 mg/L in 1 L shake flask, respectively, indicating that the spacer peptide could increase the expression. The expression level of PIP (sp-PIP) in P.pastoris was higher than that of PIP in S.cerevisiae and K.lactis reported in this laboratory. The expression level of sp-PIP was 250 mg/L in 10 L fermentor. Recombinant human insulin was obtained by means of transpeptidation of PIP or sp-PIP. The receptor binding capacity is identical with that of porcine insulin. In vivo biological activity of the recombinant human insulin is 27 IU/mg.