Identification of a novel human UDP-GalNAc transferase with unique catalytic activity and expression profile

A novel member of the human ppGalNAc-T family, ppGalNAc-T20, was identified and characterized. Amino acid alignment revealed a high sequence identity between ppGalNAc-T20 and -T10. In the GalNAc transfer assay towards mucin-derived peptide substrates, the recombinant ppGalNAc-T20 demonstrated to be a typical glycopeptide GalNAc-transferase that exhibits activity towards mono-GalNAc-glycosylated peptide EA2 derived from rat submandibular gland mucin but no activity towards non-modified EA2. The in vitro catalytic property of ppGalNAc-T20 was compared with that of ppGalNAc-T10 to show different acceptor substrate specificities and kinetic constants. The ppGalNAc-T20 transcript was found exclusively in testis and brain. In situ hybridization further reveals that ppGalNAc-T20 was specifically localized in primary and secondary spermatocytes of the two meiotic periods, suggesting that it may involve in O-glycosylation during mouse spermatogenesis.

Research highlights
► Identification of a novel member of human ppGalNAc-T family, ppGalNAc-T20, which shares high sequence homology to ppGalNAc-T10.
► ppGalNAc-T20 demonstrated to be a typical glycopeptide GalNAc-transferase that has different substrate specificity and catalytic efficiency from ppGalNAc-T10.
► ppGalNAc-T20 was restrictively expressed in testis and brain, in particular, it was specifically localized in spermatocytes of meiotic periods.
► The activity and expression profile of 20 human ppGalNAc-Ts was summarized to provide us a systematic model to investigate O-glycosylation.