A single amino acid residue determines the ratio of hydrolysis to transglycosylation catalyzed by β-glucosidases

The propensity to catalysis of transglycosylation of the β-glucosidase tmβgly is higher than for sfβgly. moreover the propensity to catalysis of transglycosylation is directly proportional to the substrate concentration for tmβgly,whereas for sfβgly it is constant. for instance,60% of a tmβgly sample catalyzes transglycosylation reactions at 40 mm p-nitrophenyl β-glucoside,whereas only 40% is engaged in hydrolysis of this substrate. for sfβgly the fraction involved in transglycosylation is only 30 %. in addition,48 % of a tmβgly sample catalyzes transglycosylation reactions at 8 mm methylumbelliferyl β-glucoside,whereas sfβgly does not catalyze transglycosylation using this substrate. interestingly,these tmβgly properties were grafted into sfβgly by a single replacement of a residue forming a channel involved in supplying the catalytic water molecules for attack on the covalent intermediate present in the reaction catalyzed by β-glucosidases. hence a single residue determines the ratio of hydrolysis to transglycosylation reactions catalyzed by these β-glucosidases. © 2013 bentham science publishers.