Pichia pastoris has been reported as a better expression host compared to Escherichia coli for producing various heterologous proteins. Gene encoding thermostable lipases Itb1.1 and Lk3 were previously expressed in E. coli with low specific activity. In this study, the genes were subcloned successfully into Pichia expression vector pPICZαA and integrated into the genome of P. pastoris GS115. The yeast transformants were grown in buffered methanolcomplex medium with methanol induction to express the proteins. Meanwhile, E. coli BL21 (DE3) recombinants were regenerated in Luria Bertani with isopropyl β-d-1-thiogalactopyranoside induction to express the proteins. Purified proteins were obtained through nickel-nitrilotriacetic acid affinity chromatography. The lipolytic activity assay was conducted at pH 8 and 70°C for Itb1.1 and pH 8 and 50°C for Lk3. The specific activity of Itb1.1 expressed in E. coli cells was 1.2064 U/mg, whereas that of the enzyme expressed in P. pastoris was 7.6836 U/mg. Moreover, the specific activity of Lk3 expressed in E. coli was 0.3523 U/mg, whereas that in P. pastoris was 4.8508 U/mg. Therefore, the specific activity of Itb1.1 and Lk3 expressed in P. pastoris was 6 and 14 times higher than that expressed in E. coli, respectively. The data suggested that P. pastoris is a better host for the expression of Itb1.1 and Lk3 proteins.
Key words: heterologous expression, thermostable lipase, Escherichia coli, Pichia pastoris