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Beschreibung

Polypeptide N-acetylgalactosaminyltransferase 5 (UniProt: Q7Z7M9, also known as EC:2.4.1.41, Polypeptide GalNAc transferase 5, GalNAc-T5, pp-GaNTase 5, Protein-UDP acetylgalactosaminyltransferase 5, UDP-GalNAc:polypeptide N-acetylgalactosaminyltransferase 5) is encoded by the GALNT5 gene (Gene ID: 11227) in human. Complex carbohydrates synthesis in mammals involves over 200 distinct glycosyltransferases that differ in their cellular expression and their glycosylation capacity. A majority of them are localized in the endoplasmic reticulum or Golgi and their specific subcellular localization is believed to be distributed in the secretory pathway according to their sequential role in the glycosylation process. GalNAc-T5 is a single-pass type II membrane glycoprotein with a cytoplasmic domain (aa 1-12), a transmembrane domain (aa 13-35), and a lumenal domain (aa 36-940). It catalyzes the initial reaction in O-linked oligosaccharide biosynthesis, the transfer of an N-acetyl-D-galactosamine residue to a serine or threonine residue on the protein receptor. It displays activity toward EA2 peptide substrates but has a weak activity toward Muc2 or Muc1b substrates. GalNAc-T5 has two conserved domains in the glycosyltransferase region: the N-terminal domain (domain A, also called GT1 motif) that is probably involved in manganese coordination and substrate binding and the C-terminal domain (domain B, also called Gal/GalNAc-T motif) that is involved in catalytic reaction and UDP-Gal binding. It also contains a ricin B-type lectin domain (aa 804-935) that binds to GalNAc and contributes to the glycopeptide specificity. Strong expression of GalNAc-T5 has been reported in normal gastric epithelium and in gastric cancer cells. However, its expression in normal gastric tissues is limited to a perinuclear Golgi-like localization and it is expressed throughout the cytoplasm of gastric cancer cells. (Ref.: Steentoft, C., et al. (2019). Glycobiology. 29(9), 645-656, Campos, D., et al. (2015). Mol. Cell. Proteomics. 14(6), 1616-1629).