The complex-type of oligosaccharides are synthesised through elongation by glycosyltransferases after trimming of the precursor oligosaccharides transferred to proteins in the endoplasmic reticulum. N-Acetylglucosaminyltransferases (GnTs) take part in the formation of branches in the biosynthesis of complex-type sugar chains. In vertebrates, six GnTs, designated as GnT-I to -VI, which catalyse the transfer of GlcNAc to the core mannose residues of Asn-linked sugar chains, have been identified. GnT-IV (EC:2.4.1.145) catalyses the transfer of GlcNAc from UDP-GlcNAc to the GlcNAc1-2Man1-3 arm of core oligosaccharide [Gn2(22)core oligosaccharide] and forms GlcNAc1-4(GlcNAc1-2)Man1-3 structure on the core oligosaccharide (Gn3(2,4,2)core oligosaccharide). In some members the conserved region occupies all but the very for N-terminal, where there is a signal sequence on all members. For other members the conserved region does not occupy the entire protein but is still to the N-terminus of the protein [1].

1: Purification and characterization of UDP-N-acetylglucosamine: alpha1,3-D-mannoside beta1,4-N-acetylglucosaminyltransferase (N-acetylglucosaminyltransferase-IV) from bovine small intestine. Oguri S, Minowa MT, Ihara Y, Taniguchi N, Ikenaga H, Takeuchi M; J Biol Chem 1997;272:22721-22727. PMID:9278430

2: An evolving hierarchical family classification for glycosyltransferases. Coutinho PM, Deleury E, Davies GJ, Henrissat B; J Mol Biol 2003;328:307-317. PMID:12691742