B4GALT4

This gene encodes beta-1,4-galactosyltransferase 4 that is involved in the synthesis of the Type 2 carbohydrate antigen (Galb1-4GlcNAc-R). This enzyme has the activity that transfers a Gal from the donor UDP-Gal to the GlcNAc of the non-reducing terminal of the acceptor by the b1-4 bond. In particular, it is involved in the synthesis of the carbohydrate chains of the glycolipids (nLc4Cer; paragloboside or nLc6Cer etc.). It also synthesizes the keratan sulfate proteoglycan by the transfer of a galactose to the GlcNAc 6-O-sulfate structure such as SO3 -6GlcNAc b1-3Galb1-4 (SO3-6)GlcNAc. The GlcNAcb1-2Man (synthesized by MGAT1) has the highest specificity (reactivity) to the agalacto type N-linked oligosaccharides (4-chain). First, it transfers a galactose to this position, after that it tends to transfer a galactose to GlcNAcb1-4Man (synthesized by MGAT4) or to GlcNAcb1-4Man (synthesized by MGAT2), with almost equal probability. However, there are reports that it does not show activity on glycoproteins. It is involved in the biosynthesis of the type 2 glycolipids (Galb1-4GlaNAcb1-3Galb1-4Glca-Cer or Galb1-4GlaNAcb1-3Galb1-4GlaNAcb1-3Galb1-4Glca-Cer). There are also reports that it is also involved in the synthesis of the lactosamine extended on the core 2 type O-glycan.