Unexpected regioselectivity of Humicola insolens Cel7B glycosynthase mutants

Four Humicola insolens Ce17B glycoside hydrolase mutants have been evaluated for the coupling of lactosyl fluoride on O-allyl N-I-acetyl-2(II)-azido-beta-chitobioside. Double mutants Ce17B E197A H209A and Ce1713 E197A H209G preferentially catalyze the formation of a beta-(1 -> 4) linkage between the two disaccharides, while single mutant Cel7B E197A and triple mutant Cel7B E197A H209A A211T produce predominantly the beta-(1 -> 3)-linked tetrasaccharide. This result constitutes the first report of the modulation of the regioselectivity through site-directed mutagenesis for an endoglycosynthase. (c) 2007 Elsevier Ltd. All rights reserved.