This is a family of eukaryotic ER membrane proteins that are involved in the synthesis of glycosylphosphatidylinositol (GPI), a glycolipid that anchors many proteins to the eukaryotic cell surface. Proteins in this family are involved in transferring the second mannose in the biosynthetic pathway of GPI [1] [2].

1: PIG-V Involved in Transferring the Second Mannose in Glycosylphosphatidylinositol. Kang JY, Hong Y, Ashida H, Shishioh N, Murakami Y, Morita YS, Maeda Y, Kinoshita T; J Biol Chem 2005;280:9489-9497. PMID:15623507

2: Saccharomyces cerevisiae Ybr004c and its human homologue are required for addition of the second mannose during glycosylphosphatidylinositol precursor assembly. Fabre AL, Orlean P, Taron CH; FEBS J 2005;272:1160-1168. PMID:15720390