Using simple donors to drive the equilibria of glycosyltransferase-catalyzed reactions

A systematic analysis of possible substrates for reverse glycosyltransferase reactions reveals thermodynamically favored pathways to the traditional 'activated' sugar donors, enabling high-yielding enzymatically coupled sugar transfers and a general colorimetric assay for sugar nucleotide formation and utilization. We report that simple glycoside donors can drastically shift the equilibria of glycosyltransferase-catalyzed reactions, transforming NDP-sugar formation from an endothermic to an exothermic process. To demonstrate the utility of this thermodynamic adaptability, we highlight the glycosyltransferase-catalyzed synthesis of 22 sugar nucleotides from simple aromatic sugar donors, as well as the corresponding in situ formation of sugar nucleotides as a driving force in the context of glycosyltransferase-catalyzed reactions for small-molecule glycodiversification. These simple aromatic donors also enabled a general colorimetric assay for glycosyltransfer, applicable to drug discovery, protein engineering and other fundamental sugar nucleotide–dependent investigations. This study directly challenges the general notion that NDP-sugars are 'high-energy' sugar donors when taken out of their traditional biological context.