Optimization of Expression Conditions for Milk-derived Immune Peptides in E.coli BL21

The target genes of 4 previously reported milk-derived immuno-modulating peptides were designed,and the prokaryotic expression plasmid pTYB11 with the target genes was then constructed and transformed into E.coli BL21 by recombinant DNA technique.Expression conditions such as IPTG concentration,expression temperature and expression time of the plasmid encoded milk-derived immune peptides in E.coli BL21 cells were optimized by orthogonal array design.The quantitative analysis of the fusion protein by 15% SDA-PAGE showed that the optimal expression conditions were the induction of IPTG at the concentration of 0.1-0.2 mmol/L,and expression temperature of 12-15℃ for 20 h.A 59.2 kD fusion protein was identified in Western Blotting and its expression amount was found to account for 40% of total proteins.