May play a role in male spermatogenesis. In vitro acts as inhibitor of MGAT1 activity causing cell surface proteins to carry mainly high mannose N-glycans. The function is mediated by its lumenal domain and occurs specifically in the Golgi. A catalytic glucosyltransferase activity is not detected. May be involved in regulation of Sertoli-germ cell interactions during specific stages of spermatogenesis. May self-associate; specifically in the endoplasmic reticulum prior to its translocation to the Golgi. Interacts with MGAT1, MGAT3 and MAN2A2; may interact with MGTA1 specifically in the Golgi. Expressed in testis. Poorly expressed in testis biopsies from men with impaired spermatogenesis. Belongs to the glycosyltransferase 54 family.