Nacetylgalactosamine6sulfate

N-acetylgalactosamine, commonly abbreviated GalNAc, is an amino sugar derivative of galactose in which the amino group at carbon 2 is acetylated. It occurs in both pyranose ring forms (alpha and beta) and is a fundamental building block of many glycoconjugates, particularly in mammals.

In biology, GalNAc serves as the initiating sugar in mucin-type O-linked glycosylation. GalNAc transferases catalyze the transfer of GalNAc from the activated donor UDP-GalNAc to serine or threonine residues on proteins, generating the Tn antigen when unextended. This GalNAc residue can be elaborated further to form diverse O-glycan structures, including core 1, core 2, and other extended glycans. UDP-GalNAc is the activated donor used by these transferases and is produced in cells from UDP-GlcNAc via metabolic interconversions.

GalNAc is also a component of glycosaminoglycans and proteoglycans, appearing in keratan sulfate disaccharides and contributing to the structure of other proteoglycans found in connective tissues. It is encountered in various glycoproteins and glycolipids throughout biology, often contributing to cellular recognition, signaling, and protein stability.

Clinical and research notes: Altered expression of GalNAc-containing structures is observed in certain cancers, and the Tn antigen is studied as a tumor-associated carbohydrate antigen with potential diagnostic and therapeutic applications. Beyond glycobiology, GalNAc residues are used as ligands in biotechnology and as targets for lectin-based detection.