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Carbohydr Res. 2006 Sep 4;341(12):2055-65. Epub 2006 May 23.

Acceptor-dependent regioselectivity of glycosynthase reactions by Streptomyces E383A beta-glucosidase.

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1
Laboratory of Biochemistry, Institut Químic de Sarrià, Universitat Ramon Llull, Via Augusta 390, E-08017 Barcelona, Spain.

Abstract

The nonnucleophilic mutant E383A beta-glucosidase from Streptomyces sp. has proven to be an efficient glycosynthase enzyme, catalyzing the condensation of alpha-glucosyl and alpha-galactosyl fluoride donors to a variety of acceptors. The enzyme has maximal activity at 45 degrees C, and a pH-dependence reflecting general base catalysis with an apparent kinetic pKa of 7.2. The regioselectivity of the new glycosidic linkage depends unexpectedly on the acceptor substrate. With aryl monosaccharide acceptors, beta-(1-->3) disaccharides are obtained in good to excellent yields, thus expanding the synthetic products available with current exo-glycosynthases. With xylopyranosyl acceptor, regioselectivity is poorer and results in the formation of a mixture of beta-(1-->3) and beta-(1-->4) linkages. In contrast, disaccharide acceptors produce exclusively beta-(1-->4) linkages. Therefore, the presence of a glycosyl unit in subsite +II redirects regioselectivity from beta-(1-->3) to beta-(1-->4). To improve operational performance, the E383A mutant was immobilized on a Ni2+-chelating Sepharose resin. Immobilization did not increase stability to pH and organic solvents, but the operational stability and storage stability were clearly enhanced for recycling and scaling-up.

PMID:
16716271
DOI:
10.1016/j.carres.2006.04.049
[Indexed for MEDLINE]

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