Post-GPI attachment to proteins factor 4 (PGAP4), also known as post-GPI attachment to proteins GalNAc transferase 4 or transmembrane protein 246 (TMEM246), has been shown to be a Golgi-resident GPI-GalNAc transferase. Many eukaryotic proteins are anchored to the cell surface through glycolipid glycosylphosphatidylinositol (GPI). GPIs have a conserved core but exhibit diverse N-acetylgalactosamine (GalNAc) modifications. PGAP4 knockout cells lose GPI-GalNAc structures. PGAP4 is most likely involved in the initial steps of GPI-GalNAc biosynthesis. In contrast to other Golgi glycotransferases (GTs), it contains three transmembrane domains. Structural modeling suggests that PGAP4 adopts a GT-A fold split by an insertion of tandem transmembrane domains.
Jiyao W et al.(2023). "The conserved domain database in 2023.",