Mechanistic insight into the substrate specificity of 1,2-?-oligoglucan phosphorylase from Lachnoclostridium phytofermentans.

ABSTRACT: Glycoside phosphorylases catalyze the phosphorolysis of oligosaccharides into sugar phosphates. Recently, we found a novel phosphorylase acting on ?-1,2-glucooligosaccharides with degrees of polymerization of 3 or more (1,2-?-oligoglucan phosphorylase, SOGP) in glycoside hydrolase family (GH) 94. Here, we characterized SOGP from Lachnoclostridium phytofermentans (LpSOGP) and determined its crystal structure. LpSOGP is a monomeric enzyme that contains a unique ?-sandwich domain (Ndom1) at its N-terminus. Unlike the dimeric GH94 enzymes possessing catalytic pockets at their dimer interface, LpSOGP has a catalytic pocket between Ndom1 and the catalytic domain. In the complex structure of LpSOGP with sophorose, sophorose binds at subsites +1 to +2. Notably, the Glc moiety at subsite +1 is flipped compared with the corresponding ligands in other GH94 enzymes. This inversion suggests the great distortion of the glycosidic bond between subsites -1 and +1, which is likely unfavorable for substrate binding. Compensation for this disadvantage at subsite +2 can be accounted for by the small distortion of the glycosidic bond in the sophorose molecule. Therefore, the binding mode at subsites +1 and +2 defines the substrate specificity of LpSOGP, which provides mechanistic insights into the substrate specificity of a phosphorylase acting on ?-1,2-glucooligosaccharides.

SUBMITTER: Nakajima M 

PROVIDER: S-EPMC5309861 | biostudies-literature | 2017 Feb

REPOSITORIES: biostudies-literature