From β-glucanase to β-glucansynthase: Glycosyl transfer to α-glycosyl fluorides catalyzed by a mutant endoglucanase lacking its catalytic nucleophile

Removal of the catalytic nucleophile Glu134 of the retaining 1,3-1,4-β-glucanase from Bacillus licheniformis by mutation to alanine yields an enzyme with no glycosidase activity. The mutant is able to catalyze the regio- and stereospecific glycosylation of α-laminaribiosyl fluoride with different glucoside acceptors through a single-step inverting mechanism. The main advantage of the mutant as glycosylation catalyst with respect to the kinetically controlled transglycosylation using the wild-type enzyme is that the reaction products cannot be hydrolyzed by the mutant enzyme, and glycosylation yields rise to 90%. Copyright (C) 1998 Federation of European Biochemical Societies.