Structures and mechanisms of glycosyltransferases

Abstract

Glycosyltransferases (GTs) catalyze the transfer of a sugar moiety from an activated donor sugar onto saccharide and nonsaccharide acceptors. A sequence-based classification spreads GTs in many families thus reflecting the variety of molecules that can be used as acceptors. In contrast, this enzyme family is characterized by a more conserved three-dimensional architecture. Until recently, only two different folds (GT-A and GT-B) have been identified for solved crystal structures. The recent report of a structure for a bacterial sialyltransferase allows the definition of a new fold family. Progress in the elucidation of the structures and mechanisms of GTs are discussed in this review. To accommodate the growing number of crystal structures, we created the 3D-Glycosyltransferase database to gather structural information concerning this class of enzymes.

Lyase activity of glycogen synthase: Is an elimination/addition mechanism a possible reaction pathway for retaining glycosyltransferases?

“…Such a front-face substitution was originally proposed by Klein et al (10) to explain the catalytic mechanism of glycogen phosphorylase (GP) and maltodextrin phosphorylase (MalP), two retaining GTs classified in the GT35 family that use glucose 1-phosphate (Glc-1-P) as glucosyl donor. In this and other reports (3,11,12), the S N i mechanism was described as a concerted process, a kind of front-side S N 2 attack (13), with the involvement of a single transition state (Fig. 1B).…”

“…Solely based on the electron density, this compound was assigned as 1,5-anhydrosorbitol. However, we propose that this intermediate is AA (3) or its keto tautomer AF (4).…”

“…1A). However, while the single-step S N 2-like displacement for inverting GTs has obtained experimental and theoretical support (3,4), there is no clear evidence in favor of the double displacement mechanism for retaining GTs. More specifically, although chemical rescue of inactive variants (5) and trapping of covalent glycosyl-enzyme intermediates (6, 7) have been reported, these studies used mutant enzymes with altered active sites.…”

A Membrane-located Glycosyltransferase Complex Required for Biosynthesis of the d-Galactan I Lipopolysaccharide O Antigen in Klebsiella pneumoniae

“…WbbN was initially assigned as a galactosyltransferase based on its Rossman-like fold, characteristic of the GT-A fold (34,39). The frameshift mutation of wbbN in the D-galactan I cluster eliminated formation of D-galactan I, a result entirely consistent with WbbN being a galactosyltransferase involved in the overall chain extension process.…”

“…WbbN belongs to GT-2, one of the largest families within the GT-A superfamily (34,35). Unlike WbbO and WbbM, WbbN (290 residues, 33.2 kDa) is predicted to contain a single domain (Fig.…”