Function and structure relationships of a β-1,2-glucooligosaccharide-degrading β-glucosidase.

BT_3567 protein, a putative β-glucosidase from Bacteroides thetaiotaomicron, exhibits higher activity toward Sop (Sop , n: degree of polymerization of β-1,2-glucooligosaccharides) than toward Sop , unlike a known β-glucosidase from Listeria innocua which predominantly prefers Sop . In the complex structure determined by soaking of a D286N mutant crystal with Sop , a Sop moiety was observed at subsites -1 to +2. The glucose moiety at subsite +2 forms a hydrogen bond with Asn81, which is replaced with Gly in the L. innocua β-glucosidase. The K values of the N81G mutant for Sop are much higher than those of the wild-type, suggesting that Asn81 contributes to the binding to substrates longer than Sop .