Cloning and expression of mouse UDP-GalNAc:polypeptide N-acetylgalactosaminyltransferase-T3.

A novel isoform of UDP-GalNAc:polypeptide N-acetylgalactosaminyltransferase, designated ppGaNTase-T3, has been cloned from a mouse testis cDNA library and expressed in COS7 cells. ppGaNTase-T3 displayed 64 and 59% amino acid identity with ppGaNTase-T1 and ppGaNTase-T2, respectively, and 96% amino acid identity with the recently reported human form of ppGaNTase-T3. The ppGaNTase-T3 transcript is abundant in the major salivary glands, gastrointestinal tract and both the male and female reproductive systems. ppGaNTase-T3 and ppGaNTase-T1 display overlapping substrate preferences in vitro, although mapping studies of O-glycosylated peptides suggests that certain hydroxyamino acids are preferentially glycosylated by each isoform. This suggests that more than one isoform of ppGaNTase may be required to complete the O-glycosylation of endogenous substrates.