From beta-glucanase to beta-glucansynthase: glycosyl transfer to alpha-glycosyl fluorides catalyzed by a mutant endoglucanase lacking its catalytic nucleophile.

Removal of the catalytic nucleophile Glu134 of the retaining 1,3-1,4-beta-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 alpha-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%.