Combinatorial mutation on the β-glycosidase specific to 7-β-xylosyltaxanes and increasing the mutated enzyme production by engineering the recombinant yeast

Abstract

Taxol is a "blockbuster" antitumor drug produced by <i>Taxus</i> species with extremely low amount, while its analogue 7-<i>β</i>-xylosyl-10-deacetyltaxol is generally much higher in the plants. Both the fungal enzymes LXYL-P1-1 and LXYL-P1-2 can convert 7-<i>β</i>-xylosyl-10-deacetyltaxol into 10-deacetyltaxol for Taxol semi-synthesis. Of them, LXYL-P1-2 is twice more active than LXYL-P1-1, but there are only 11 significantly different amino acids in terms of the polarity and acidic-basic properties between them. In this study, single and multiple site-directed mutations at the 11 sites from LXYL-P1-1 to LXYL-P1-2 were performed to define the amino acids with upward bias in activities and to acquire variants with improved catalytic properties. Among all the 17 mutants, E12 (A72T/V91S) was the most active and even displayed 2.8- and 3-fold higher than LXYL-P1-2 on <i>β</i>-xylosidase and <i>β</i>-glucosidase activities. The possible mechanism for such improvement was proposed by homology modeling and molecular docking between E12 and 7-<i>β</i>-xylosyl-10-deacetyltaxol. The recombinant yeast GS115-P1E12-7 was constructed by introducing variant <i>E12</i>, the molecular chaperone gene <i>pdi</i> and the bacterial hemoglobin gene <i>vhb</i>. This engineered yeast rendered 4 times higher biomass enzyme activity than GS115-3.5K-P1-2 that had been used for demo-scale fermentation. Thus, GS115-P1E12-7 becomes a promising candidate to replace GS115-3.5K-P1-2 for industrial purpose.