ⓘ B4GALT1

                                     

ⓘ B4GALT1

Beta-1.4-galactosyltransferase 1 is an enzyme that in humans is encoded by the B4GALT1 gene.

This gene is one of seven beta 1.4-galactosyltransferase genes beta4GalT. They encode a second type of membrane-bound glycoproteins, which seem to have exceptional specificity for the substrate donor UDP-galactose; all transfer galactose in a beta1.4 relation to similar acceptor sugars: GlcNAc, GLC, and young ladies. Beta4GalT each has a separate function in the biosynthesis of various compounds and saccharide structures. As type II membrane proteins, they have N-terminal hydrophobic signal sequence that directs the protein of the Golgi apparatus and which then remains uncleaved functions as a transmembrane anchor. The similarity of the sequence beta4GalTs form four groups: beta4GalT1 and beta4GalT2, beta4GalT3 and beta4GalT4, beta4GalT5 and beta4GalT6, and beta4GalT7. This gene is unique among beta4GalT genes because it encodes an enzyme that participates both in glycoconjugate and lactose biosynthesis. For the first activity, the enzyme adds galactose to n-acetylglucosamine residues, which are monosaccharides or unrestored ends of glycoprotein carbohydrate chains. The second activity is restricted to lactating mammary tissues where the enzyme forms a heterodimer with alpha-lactalbumin to catalyze UDP-galactose and D-glucose UDP lactose. Two enzymatic forms, as a result of alternative transcription initiation sites and post-translational processing. Two transcripts that differ only at the 5 end, with approximate lengths of 4.1 KB and 3.9 KB encode the same protein. The longer transcript encodes the type of the second membrane-bound, TRANS-Golgi resident protein involved in glycoconjugate biosynthesis. The shorter transcript encodes a protein which is cleaved to form the soluble lactose synthase.