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. Testis. Detected in the Golgi apparatus of pachytene spermatocytes beginning at stage VII and extending up to stage XIV. Detected in the Golgi apparatus of spermatids at steps 1-15 of spermatogenesis. N-glycosylated. O-glycosylated; further modified with terminal sialic acid residues. Belongs to the glycosyltransferase 54 family.