Glycosyltransferase family 25 [lipooligosaccharide (LOS) biosynthesis protein] is a family of glycosyltransferases involved in LOS biosynthesis. The members include the beta(1,4) galactosyltransferases: Lgt2 of Moraxella catarrhalis, LgtB and LgtE of Neisseria gonorrhoeae and Lic2A of Haemophilus influenzae. M. catarrhalis Lgt2 catalyzes the addition of galactose (Gal) to the growing chain of LOS on the cell surface. N. gonorrhoeae LgtB and LgtE link Gal-beta(1,4) to GlcNAc (N-acetylglucosamine) and Glc (glucose), respectively. The genes encoding LgtB and LgtE are two genes of a five gene locus involved in the synthesis of gonococcal LOS. LgtE is believed to perform the first step in LOS biosynthesis.

GT13_GLCNAC-TI is involved in an essential step in the synthesis of complex or hybrid-type N-linked oligosaccharides. Alpha-1,3-mannosyl-glycoprotein beta-1,2-N-acetylglucosaminyltransferase (GLCNAC-T I , GNT-I) transfers N-acetyl-D-glucosamine from UDP to high-mannose glycoprotein N-oligosaccharide, an essential step in the synthesis of complex or hybrid-type N-linked oligosaccharides. The enzyme is an integral membrane protein localized to the Golgi apparatus. The catalytic domain is located at the C-terminus. These proteins are members of the glycosy transferase family 13.

GNT-I family. Alpha-1,3-mannosyl-glycoprotein beta-1,2-N-acetylglucosaminyltransferase (GNT-I, GLCNAC-T I) EC:2.4.1.101 transfers N-acetyl-D-glucosamine from UDP to high-mannose glycoprotein N-oligosaccharide. This is an essential step in the synthesis of complex or hybrid-type N-linked oligosaccharides. The enzyme is an integral membrane protein localised to the Golgi apparatus, and is probably distributed in all tissues. The catalytic domain is located at the C-terminus.