Investigation of the rescue mechanism catalyzed by a nucleophile mutant of rice BGlu1

In the present study, the quantum mechanical/molecular mechanical (QM/MM) method was used to investigate the rescue mechanism of an E386G mutant as well as the glycosylation mechanism of the wild rice beta-D-glucosidase. E386G mutant experiences an asynchronous collaborative process to glycosylate the anionic formate with an energy barrier of 22.6 kcal/mol, while the energy barrier is 25.9 kcal/mol for the wild complex. The low energy barrier of the mutated complex suggests that anionic formate might be a good nucleophile to attack the anomeric carbon atom. Both energy barriers can be lowered when the leaving departure releases from the active site, suggesting that the product release, rather than chemistry, contributes to the rate limiting in BGlu1 mutants. Structure analyses also indicate that the external nucleophile has little steric hindrance with pocket residues and adjusts freely to proceed the rescue mechanism of the mutated complex. Our calculations provide a guide for the selectivity of exogenous nucleophiles in the future study of beta-glucosidase. (C) 2014 Elsevier Inc. All rights reserved.