Mechanistic analogies amongst carbohydrate modifying enzymes

Abstract

Carbohydrates are known to play essential roles in a myriad of biological processes. The enormous complexity of the various oligosaccharide structures found in biology is derived from a rational orchestration of the enzymatic formation and breakdown of glycosidic linkages achieved by glycosyltransferases, glycosidases and phosphorylases. A detailed understanding of the chemical mechanisms by which these classes of enzymes function not only provides a rational basis for their engineering and application in both the development and synthesis of new classes of therapeutic agents, but also provides insight into the role of convergence in the natural evolution of enzyme function.

Structural and Enzymatic Analysis of MshA from Corynebacterium glutamicum

“…Significant normal ␣-deuterium secondary isotope effects have been reported for inverting and retaining glycosyltransferases (45)(46)(47) and glycosidases (48,49) consistent with C1-O bond cleavage occurring prior to attack by the acceptor sugar or water. For inverting glycosidases and glycosyltransferases, the proposed single displacement mechanism is well established (50). There is also structural and kinetic evidence that retaining glycosidases follow a double displacement mechanism with participation of a covalent enzyme-substrate intermediate (49,51).…”

“…The dissociative nature of the transition state may be further stabilized by Arg-261, which forms an ion pair with the ␤-phosphate. A comparison of the active site architecture of CgMshA with other retaining glycosyltransferases suggests that the bent-back conformation of the donor molecule and the interaction of the ␤-phosphate with a positive charge (typically an arginine or metal ion) is a conserved feature of retaining glycosyltransferases (50,57).…”

Aromatic interactions at the catalytic subsite of sucrose phosphorylase: Their roles in enzymatic glucosyl transfer probed with Phe52 → Ala and Phe52 → Asn mutants

“…Stabilization of oxocarbenium ion-like transition states by cation-p interactions could therefore be a common theme of catalysis by the members of this family. Several other enzymes [10,[37][38][39][40][41], among them glycosyltransferases [8,10] that show significant mechanistic analogy to glycoside hydrolases [42], have been proposed to stabilize (partial) positive charges in intermediates or transition states of their reaction, by up to 4 kcal/mol [37], with the help of p bonding interactions.…”

Enhancing the Latent Nucleotide Triphosphate Flexibility of the Glucose-1-phosphate Thymidylyltransferase RmlA

“…Yet, despite the vast structural and functional diversity of natural glycoconjugates, they are constructed via a common biosynthetic theme. Specifically, sugars are attached to most proteins, lipids, carbohydrates, and small molecules by glycosyltransferases, which with few exceptions use sugar nucleotides as the monosaccharide donors (3)(4)(5)(6)(7). These sugar nucleotides are constructed from sugar-1-phosphates and NTPs by sugar-1-phosphate nucleotidyltransferases, also referred to as sugar nucleotide pyrophosphorylases (EC 2.7.7.-), providing the precursors (usually ADP-, CDP-, GDP-, UDP-and dTDP-glucoses, as well as GDP-mannose, GDP-fucose, and UDP-N-acetylglucosamine) central to nearly all glycosylation-dependent processes (4,6).…”