Unexpected regioselectivity of Humicola insolens Cel7B glycosynthase mutants

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

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