glycosyltransférases

Glycosyltransférases are enzymes that catalyze the transfer of sugar moieties from activated donor molecules to acceptor substrates, forming glycosidic bonds. The most common donors are nucleotide-sugars such as UDP-sugars and GDP-sugars; other donors include TDP- and CDP-sugars. Acceptors include hydroxyl groups on proteins and lipids, growing oligosaccharides, and polysaccharide backbones. Thus glycosyltransférases participate in protein and lipid glycosylation, as well as the biosynthesis of polysaccharides, glycosaminoglycans, and secondary metabolites.

There are two principal catalytic mechanisms. Inverting glycosyltransférases operate by a single-displacement reaction that typically inverts the anomeric configuration; retaining glycosyltransférases use a two-step process that preserves configuration, often involving a glycosyl-enzyme intermediate.

The enzyme's structure classifies into GT-A and GT-B folds; many GT-A enzymes require a divalent metal ion, coordinated by a DXD motif, whereas GT-B enzymes typically do not.

Biological roles are diverse: in eukaryotes, many glycosyltransférases function in the endoplasmic reticulum and Golgi apparatus to elaborate protein and lipid glycans; in bacteria, they contribute to cell-surface polysaccharides and antibiotics biosynthesis.

Abnormal glycosyltransférase activity or deficiency can cause congenital disorders of glycosylation and other diseases, while their specificity is exploited in biotechnology and pharmaceutical synthesis for producing glycosylated compounds.