polypeptide N-acetylgalactosaminyltransferase 12 (protein-UDP acetylgalactosaminyltransferase 12, UDP-GalNAc:polypeptide N-acetylgalactosaminyltransferase 12, polypeptide GalNAc transferase 12, GalNAc-T12, pp-GaNTase 12, GALNT12)

Function

• catalyzes initial reaction in O-linked oligosaccharide biosynthesis, transfer of an N-acetyl-D-galactosamine to Ser or Thr on the nascent glycoprotein
• activity toward non-glycosylated peptides, including Muc5AC, Muc1a & EA2
• no detectable activity with Muc2 & Muc7
• enzymatic activity toward the Gal-NAc-Muc5AC glycopeptide
• no detectable activity to mono-GalNAc-glycosylated Muc1a, Muc2, Muc7 & EA2
• role in initial step of mucin-type oligosaccharide biosynthesis in digestive organs

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

Cofactor: Mn+2, Ca+2

Structure

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

Compartment

Golgi membrane

Alternative splicing

named isoforms=2 Expresison:

• widely expressed
• expressed in digestive organs (intestine, stomach, pancreas, colon) > testis, thyroid, spleen> brain, cerebral cortex, cerebellum, fetal brain, bone marrow, thymus, leukocytes, heart, skeletal muscle, liver, lung, esophagus, kidney, adrenal gland, mammary gland, uterus, placenta, ovary, prostate

More general terms

• polypeptide N-acetylgalactosaminyltransferase
• membrane protein

Database

• UniProt: http://www.uniprot.org/uniprot/Q8IXK2.html