polypeptide N-acetylgalactosaminyltransferase 9 (protein-UDP acetylgalactosaminyltransferase 9, UDP-GalNAc:polypeptide N-acetylgalactosaminyltransferase 9, polypeptide GalNAc transferase 9, GalNAc-T9, pp-GaNTase 9, GALNT9)

Function

• glycosylation
• catalyzes initial reaction in O-linked oligosaccharide biosynthesis, transfer of an N-acetyl-D-galactosamine residue to Ser or Thr on protein receptor
• does not glycosylate apomucin or SDC3

UDP-N-acetyl-D-galactosamine + polypeptide

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UDP + N-acetyl-D-galactosaminyl-polypeptide

Cofactor: Mn+2, Ca+2

Structure

• belongs to the glycosyltransferase 2 family, GalNAc-T subfamily.
• contains 1 ricin B-type lectin domain
  • ricin B-type lectin domain binds to GalNAc & contributes to the glycopeptide specificity
• 2 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 membrane

Alternative splicing

named isoforms=2

Expression

• specifically expressed in brain
• not expressed in heart, placenta, lung, liver, skeletal muscle, kidney, pancreas, spleen, thymus, prostate, testis, ovary, small intestine, colon and leukocyte
• in brain, it is expressed in cerebellum, frontal lobe, temporal lobe, putamen, spinal cord
  • weakly expressed in cerebral cortex
  • not expressed in medulla & occipital pole

More general terms

• polypeptide N-acetylgalactosaminyltransferase

Database

• OMIM: https://mirror.omim.org/entry/606251
• UniProt: http://www.uniprot.org/uniprot/Q9HCQ5.html