Polypeptide a-GalNAc-transferases

Polypeptide a-GalNAc transferase initiates O-glycan synthesis by attachment of GalNAc to Ser/Thr resides of proteins. There does not appear to be a specific amino acid sequence signal for GalNAc transfer however, Pro is often... 

The first step of O-glycosylation is catalyzed by enzymes comprising a family of polypeptide a-GalNAc-transferases. Genes encoding this ubiquitous enzyme have been cloned from several mammalian species [16, 17]. 

In animals, the typical mucin-type glycosylation is initiated by the transfer of GalNAc by a number of different enz)mies about twenty polypeptide-modifying GalNAc transferases... 

A) Human GalNAc-l-P kinase, (B) human UDP-GalNAc pyrophosphorylase, (C) bovine polypeptide GalNAc-transferase, (D) rabbit creatine kinase and (E) inorganic pyrophosphatase. 

Glycosyltransferases also appear to have extended acceptor-binding sites that allow a variety of different substrates to bind, provided that they have specific structural features. Many of the glycosyltransferases also have posttranslational modifications such as N-glycosylation, which may be required for their stability, secretion, and activity. The first enzyme in the pathway, polypeptide GalNAc-transferase, is unique in that it has a separate lectin-like domain, which may have a role in determining the affinity to already glycosylated acceptor substrates. 

Clausen, H. and Bennett, E.P. A family of UDP-GalNAc polypeptide N-acetylgalactosaminyl-transferases control the initiation of mucin-type O-linked glycosylation. Glycobiology 6 635-646, 1996. 

Wang, Y., Agrwal, N., Eckhardt, A.E., Stevens, R.D., and Hill, R.L. The acceptor substrate specificity of porcine submaxillary UDP- GalNAc polypeptide N-acetylgalactosaminyl-transferase is dependent on the amino acid sequences adjacent to serine and threonine residues. J. Biol. Chem. 268 22979-22983, 1993. 

Bennett EP, Mandel U, Clausen H et al (2011) Control of mucin-type O-glycosylation— a classification of the polypeptide GalNAc-transferase gene femQy. Glycobiology 22 736-756... 

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