Trapping and retaining intermediates in glycosyltransferases

Abstract

Glycosyltransferases (GTs) attach sugar molecules to a broad range of acceptors, generating a remarkable amount of structural diversity in biological systems. GTs are classified as either "retaining" or "inverting" enzymes. Most retaining GTs typically use an S_Ni mechanism. In a recent article in the JBC, Doyle et al. demonstrate a covalent intermediate in the dual-module KpsC GT (GT107) supporting a double displacement mechanism.

Keywords: CAZyme; Escherichia coli; capsular polysaccharide; cell surface; enzyme catalysis; enzyme mechanism; enzyme structure; glycolipid biosynthesis; glycosyltransferase.

Figure 1

Proposed reaction mechanisms for ‘retaining’ GTs.A, GT enzymes are classified in ‘retaining’ or ‘inverting’ depending of the anomeric configuration of reactants and products. B, two potential mechanisms have been proposed for ‘retaining’ GTs, a double-displacement and an S_Ni mechanisms. C, ternary complex of a ‘retaining’ GT enzyme following the proposed S_Ni mechanism: GpgS (PDB 4Y6N) (8). D, details of the interactions made by the WbbB Asn232Cys mutant with the α-Kdo covalent intermediate adduct and acceptor disaccharide in the active site (PDB 8CSF) (9). E, details of the interactions made by the KpsC-NEc Asp160Cys mutant in complex with CMP, the Kdo covalent intermediate adduct and the acceptor in the active site (PDB 8FUX) (10).