This family represents the Golgi-resident GPI-GalNAc transferase PGAP4 (also known as TMEM246). It contains three transmembrane domains, this contrasts with other Golgi glycosyltransferases composed of a single domain. It contains a catalytic site, a DXD-like motif for UDP-GalNAc donor binding and residues thought to be involved in acceptor binding. PGAP4 is required for the initial step of GPI-GalNAc biosynthesis [].