Stepwise synthesis of chitooligosaccharides through a transition-state analogue substrate catalyzed by mutants of chitinase A1 from Bacillus circulans WL-12

Abstract

AbstractSeveral mutants of chitinase A1 fromBacillus circulansWL-12 have been prepared by site-directed mutagenesis of tryptophan 433. The hydrolytic activity of these mutants towardp-nitrophenyl chitobioside was lower than that of wild-type chitinase A1. The mutants were found to catalyze the transglycosylation reaction of the 1,2-oxazoline derivative ofN-acetyllactosamine (Gal-GlcNAc-oxa) toN,N′′-diacetylchitobiose (GlcNAc-GlcNAc), giving rise to a transglycosylated tetrasaccharide product (Gal-GlcNAc-GlcNAc-GlcNAc) in high yield. Based on these results, a one-pot synthesis of chitooligosaccharides by combined use of mutant W433Y and β-galactosidase has been demonstrated. By controlling the reaction conditions, chitotriose and chitotetraose were obtained in 74% and 40% yield (determined by HPLC), respectively, without isolating any intermediate products.