Mannosyltransferases

Mannosyltransferases are enzymes that catalyze the transfer of mannose, a hexose sugar, from activated donors to acceptor molecules. They participate in the formation of glycosidic bonds during the biosynthesis of oligosaccharides, glycoproteins, glycolipids and cell-wall polysaccharides. Common mannose donors include dolichol-phosphate-mannose and GDP-mannose, and acceptors can be proteins, lipids or growing carbohydrate chains.

These enzymes are widely distributed across all domains of life and are typically membrane-associated, functioning in the endoplasmic reticulum or Golgi apparatus in eukaryotes and at the cytoplasmic membrane in prokaryotes. Subfamilies include protein O-mannosyltransferases (e.g., POMT1 and POMT2 in mammals, PMT family in yeast) involved in O-linked protein glycosylation, and the ALG series of mannosyltransferases that contribute to N-linked glycan assembly on dolichol carriers. Bacterial and fungal mannosyltransferases synthesize surface structures such as lipopolysaccharide cores and mannans.

Biologically, mannosyltransferases are important for protein folding, stability, cell-cell recognition, and cell wall integrity. Defects in specific enzymes can cause human diseases; for example, mutations in POMT genes are associated with congenital muscular dystrophies and dystroglycanopathies. Because of their central role in glycosylation, mannosyltransferases are studied as potential targets for antifungal agents and therapeutics that modulate glycan-dependent processes.