Glycosyltransferase family A (GT-A) includes diverse families of glycosyl transferases with a common GT-A type structural fold. Glycosyltransferases (GTs) are enzymes that synthesize oligosaccharides, polysaccharides, and glycoconjugates by transferring the sugar moiety from an activated nucleotide-sugar donor to an acceptor molecule, which may be a growing oligosaccharide, a lipid, or a protein. Based on the stereochemistry of the donor and acceptor molecules, GTs are classified as either retaining or inverting enzymes. To date, all GT structures adopt one of two possible folds, termed GT-A fold and GT-B fold. This hierarchy includes diverse families of glycosyl transferases with a common GT-A type structural fold, which has two tightly associated beta/alpha/beta domains that tend to form a continuous central sheet of at least eight beta-strands. The majority of the proteins in this superfamily are Glycosyltransferase family 2 (GT-2) proteins. But it also includes families GT-43, GT-6, GT-8, GT13 and GT-7; which are evolutionarily related to GT-2 and share structure similarities.

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.