glycosyltransferaasit

Glycosyltransferases, sometimes misspelled as glycosyltransferaasit, are enzymes that catalyze the transfer of sugar residues from activated donor molecules to acceptor molecules. This reaction forms a glycosidic bond and is a key step in the biosynthesis of glycoconjugates, glycans, and glycolipids. Common sugar donors include UDP-glucose, UDP-galactose, GDP-mannose, and GDP-glucose, while acceptors can be proteins, lipids, or carbohydrates.

Glycosyltransferases operate by two general mechanistic classes: retaining and inverting, which refer to whether the anomeric configuration of the transferred sugar is retained or inverted. Most are classified into families GT-A or GT-B folds; GT-A enzymes often require a divalent metal ion and have a DXD motif that coordinates the metal, whereas GT-B enzymes typically accomplish catalysis with two Rossmann-like domains and may not require metal. Classification into CAZy families (GT1, GT2, etc.) is based on amino acid sequence similarity and often correlates with donor and acceptor specificities.

In eukaryotes many glycosyltransferases reside in the Golgi apparatus or endoplasmic reticulum and act in protein and lipid glycosylation, whereas in bacteria they participate in cell wall polysaccharide and lipopolysaccharide biosynthesis. The enzyme class is essential for proper folding, stability, and signaling of glycoproteins and for the structural integrity of cell walls and membranes.

Most glycosyltransferases are assigned EC numbers in the 2.4.x.x subclass of transferases, reflecting their role in transferring sugar residues.