Glycosynthases-retaining glycosidases mutated at their catalytic nucleophile-catalyze the formation of glycosidic bonds from glycosyl fluorides as donor sugars and various glycosides as acceptor sugars. Here the first glycosynthase derived from a family 35 β-galactosidase is described. The Glu→Gly mutant of BgaC from Bacillus circulans (BgaC-E233G) catalyzed regioselective galactosylation at the 3-position of the sugar acceptors with α-galactosyl fluoride as the donor. Transfer to 4-nitophenyl α-D-N-acetyl-glucosaminide and α-D-N-acetylgalactosaminide yielded 4-nitophenyl α-lacto-N-biose and α-galacto-N-biose, respectively, in high yields (up to 98%). Kinetic analysis revealed that the high affinity of the acceptors contributed mostly to the BgaC-E233G-catalyzed transglycosylation. BgaC-E233G showed no activity with β-(1,3)-linked disaccharides as acceptors, thus suggesting that this enzyme can be used in "one-pot synthesis" of LNB- or GNB-containing glycans.
Keywords: beta-galactosidase; glycosylation; glycosynthase; regioselectivity; transglycosylation.
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