B4GALT1

这个基因是7个β-1，4-半乳糖基转移酶（beta4galt）基因之一。它们编码对供体底物udp半乳糖具有特异性的Ⅱ型膜结合糖蛋白；所有以β1,4连接的半乳糖转移到类似的受体糖：glcnac、glc和xyl。每种β4谷丙转氨酶在不同糖缀合物和糖结构的生物合成中具有不同的功能。作为II型膜蛋白，它们具有一个N端疏水信号序列，该序列将蛋白质引导到高尔基体，然后其作为跨膜锚的功能仍不清楚。通过序列相似性，beta4galt1和beta4galt2、beta4galt3和beta4galt4、beta4galt5和beta4galt6和beta4galt7形成了四组。这个基因在beta4galt基因中是唯一的，因为它编码一种参与糖缀合物和乳糖生物合成的酶。对于第一个活性，这种酶将半乳糖添加到作为单糖或糖蛋白碳水化合物链的非还原端的N-乙酰氨基葡萄糖残基中。第二种活性仅限于哺乳期乳腺组织，其中酶与α-乳清蛋白形成异二聚体来催化UDP半乳糖+D-葡萄糖<=>UDP+乳糖。这两种酶的形式来源于交替的转录起始位点和翻译后加工。两个仅在5'末端不同的转录物编码相同的蛋白质，长度约为4.1kb和3.9kb。较长的转录物编码参与糖共轭生物合成的Ⅱ型膜结合跨高尔基体驻留蛋白。较短的转录物编码一种被剪切形成可溶性乳糖合成酶的蛋白质。
This gene is one of seven beta-1,4-galactosyltransferase (beta4GalT) genes. They encode type II membrane-bound glycoproteins that appear to have exclusive specificity for the donor substrate UDP-galactose; all transfer galactose in a beta1,4 linkage to similar acceptor sugars: GlcNAc, Glc, and Xyl. Each beta4GalT has a distinct function in the biosynthesis of different glycoconjugates and saccharide structures. As type II membrane proteins, they have an N-terminal hydrophobic signal sequence that directs the protein to the Golgi apparatus and which then remains uncleaved to function as a transmembrane anchor. By sequence similarity, the beta4GalTs form four groups: beta4GalT1 and beta4GalT2, beta4GalT3 and beta4GalT4, beta4GalT5 and beta4GalT6, and beta4GalT7. This gene is unique among the 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 that are either monosaccharides or the nonreducing 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 + D-glucose <=> UDP + lactose. The two enzymatic forms result from alternate transcription initiation sites and post-translational processing. Two transcripts, which 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 II 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.