Effects of co-expression of molecular chaperones on heterologous soluble expression of the cold-active lipase Lip-948

The cold-active lipase gene Lip-948, cloned from Antarctic psychrotrophic bacterium Psychrobacter sp. G, was ligated into plasmid pColdI. The recombinant plasmid pColdI + Lip-948 was then transformed into Escherichia coli BL21. SDS–PAGE analysis showed that there was substantive expression of lipase LIP-948 in E. coli with a yield of about 39% of total protein, most of which was present in the inclusion body. The soluble protein LIP-948 only consisted of 1.7% of total LIP-948 with a specific activity of 66.51 U/mg. Co-expression of molecular chaperones with the pColdI + Lip-948 were also carried out. The results showed that co-expression of different chaperones led to an increase or decrease in the formation of soluble LIP-948 in varying degrees. Co-expression of pColdI + Lip-948 with chaperone pTf16 and pGro7 decreased the amount of soluble LIP-948, while the soluble expression was enhanced when pColdI + Lip-948 was co-expressed with “chaperone team” plasmids (pKJE7, pG-Tf2, pG-KJE8), respectively. LIP-948 was most efficiently expressed in soluble form when it was co-expressed with pG-KJE8, which was up to 19.8% of intracellular soluble proteins and with a specific activity of 108.77 U/mg. The soluble LIP-948 was purified with amylase affinity chromatography and its enzymatic characters were studied. The optimal temperature and pH of LIP-948 was 35 °C and 8, respectively. The activity of LIP-948 dropped dramatically after incubation at 50 °C for 15 min and was enhanced by Sr2+, Ca2+. It preferentially hydrolyzed 4-nitrophenyl esters with the shorter carbon chain.