Improving the cellobiose-hydrolysis activity and glucose-tolerance of a thermostable beta-glucosidase through rational design

摘要

beta-Glucosidase is the rate-limiting component of a cellulase-hydrolyzing reaction. Thermostability and glucose tolerance are two critical criteria of the enzyme, which practically determine its performance in industrial applications. In this study, a thermostable and glucose-tolerant beta-glucosidase (named Bg11317) belonging to the glycoside hydrolase family I was acquired from a metagenomic library of Turpan soil through functional screening. Bg11317 showed excellent thermostability and glucose-tolerance and its crystal structure was subsequently determined at a high resolution. Rational design based on the structure was conducted, producing three beneficial mutations A397R, L188A and A262S. While A397R improved the cellobiose activity by 80%, L188A and A262S increased the IC50 value of glucose from 0.8 to 1.5 M. The residues that may play a role in glucose-tolerance of GH1 beta-glucosidases were summarized and the performances of glucose-tolerant beta-glucosidases reported in recent years were discussed and compared. This study provides insights into enzymatic properties of Bgl1317 for engineering it into a powerful catalyst and beta-glucosidases in general. (C) 2019 Published by Elsevier B.V.