Combined use of GAP and AOX1 promoters and optimization of culture conditions to enhance expression of Rhizomucor miehei lipase.

Rhizo mucor miehei lipase (RML) is an industrially important enzyme, but its application is limited due to its high cost. In this study, a series of measures such as codon optimization, propeptide addition, combined use of GAP and AOX1 promoters, and optimization of culture conditions were employed to increase the expression of RML. Three transformants of the constitutive-inducible combined Pichia pastoris strains were generated by transforming the pGAPZαA-rml vector into the pPIC9K-rml/GS115 strain, which resulted in high-expression yields of RML. Using the shake flask method, highest enzyme activity corresponding to 140 U/mL was observed in the strain 3-17, which was about sixfold higher than that of pPIC9K-rml/GS115 or pGAPZαA-rml/GS115. After optimization of culture conditions by response surface methodology, the lipolytic activity of strain 3-17 reached 175 U/mL in shake flasks. An increase in the copy number simultaneously with the synergistic effect provided by two promoters led to enhanced degree of protein expression.