polypeptide N-acetylgalactosaminyltransferase 13 (protein-UDP acetylgalactosaminyltransferase 13, UDP-GalNAc:polypeptide N-acetylgalactosaminyltransferase 13, polypeptide GalNAc transferase 13, GalNAc-T13, pp-GaNTase 13, GALNT13, KIAA1918)

Function

• catalyzes the initial reaction in O-linked oligosaccharide biosynthesis, transfer of an N-acetyl-D-galactosamine to Ser or Thr on the nascent glycoprotein
• much stronger activity than GALNT1 to transfer GalNAc to mucin peptides, including Muc5Ac & Muc7
• glycosylates SDC3
• synthesis of Tn antigen in neuronal cells (putative)

UDP-N-acetyl-D-galactosamine + polypeptide  <-->
           UDP + N-acetyl-D-galactosaminyl-polypeptide

Cofactor: Mn+2, Ca+2

Structure

• contains 1 ricin B-type lectin domain
  • domain binds to GalNAc & contributes to the glycopeptide specificity
• conserved domains in the glycosyltransferase region
  • N-terminal domain (domain A, GT1 motif), role in Mn+2 coordination & substrate binding
  • C-terminal domain (domain B, Gal/GalNAc-T motif), role in catalytic reaction & UDP-Gal binding

Compartment

Golgi apparatus membrane

Alternative splicing

named isoforms=2

Expression

• expressed in neuronal cells
• expressed in fetal brain, whole adult brain, cerebral cortex, cerebellum
• not expressed in other tissues

More general terms

• polypeptide N-acetylgalactosaminyltransferase
• glycoprotein
• membrane protein

Database

• OMIM: https://mirror.omim.org/entry/608369
• UniProt: http://www.uniprot.org/uniprot/Q8IUC8.html