B4GALT1 explained

Beta-1,4-galactosyltransferase 1 is an enzyme that in humans is encoded by the B4GALT1 gene.^{[1] [2]}

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.^[2]

Further reading

• Amado M, Almeida R, Schwientek T, Clausen H . Identification and characterization of large galactosyltransferase gene families: galactosyltransferases for all functions. . Biochim. Biophys. Acta . 1473 . 1 . 35–53 . 2000 . 10580128 . 10.1016/S0304-4165(99)00168-3.
• Gerber AC, Kozdrowski I, Wyss SR, Berger EG . The charge heterogeneity of soluble human galactosyltransferases isolated from milk, amniotic fluid and malignant ascites. . Eur. J. Biochem. . 93 . 3 . 453–60 . 1979 . 33805 . 10.1111/j.1432-1033.1979.tb12843.x .
• Uejima T, Uemura M, Nozawa S, Narimatsu H . Complementary DNA cloning for galactosyltransferase associated with tumor and determination of antigenic epitopes recognized by specific monoclonal antibodies. . Cancer Res. . 52 . 22 . 6158–63 . 1992 . 1384956 .
• Lopez LC, Youakim A, Evans SC, Shur BD . Evidence for a molecular distinction between Golgi and cell surface forms of beta 1,4-galactosyltransferase. . J. Biol. Chem. . 266 . 24 . 15984–91 . 1991 . 10.1016/S0021-9258(18)98505-4 . 1714903 . free .
• Mengle-Gaw L, McCoy-Haman MF, Tiemeier DC . Genomic structure and expression of human beta-1,4-galactosyltransferase. . Biochem. Biophys. Res. Commun. . 176 . 3 . 1269–76 . 1991 . 1903938 . 10.1016/0006-291X(91)90423-5 .
• Aoki D, Appert HE, Johnson D . Analysis of the substrate binding sites of human galactosyltransferase by protein engineering . EMBO J. . 9 . 10 . 3171–8 . 1990 . 2120039 . 10.1002/j.1460-2075.1990.tb07515.x. 552046 . etal.
• Watzele G, Berger EG . Near identity of HeLa cell galactosyltransferase with the human placental enzyme . Nucleic Acids Res. . 18 . 23 . 7174 . 1991 . 2124683 . 10.1093/nar/18.23.7174 . 332820 .
• Kalyanaraman VS, Rodriguez V, Veronese F . Characterization of the secreted, native gp120 and gp160 of the human immunodeficiency virus type 1 . AIDS Res. Hum. Retroviruses . 6 . 3 . 371–80 . 1990 . 2187500 . 10.1089/aid.1990.6.371 . etal.
• Pal R, Hoke GM, Sarngadharan MG . Role of oligosaccharides in the processing and maturation of envelope glycoproteins of human immunodeficiency virus type 1 . Proc. Natl. Acad. Sci. U.S.A. . 86 . 9 . 3384–8 . 1989 . 2541446 . 10.1073/pnas.86.9.3384 . 287137 . 1989PNAS...86.3384P . free .
• Dewar RL, Vasudevachari MB, Natarajan V, Salzman NP . Biosynthesis and processing of human immunodeficiency virus type 1 envelope glycoproteins: effects of monensin on glycosylation and transport . J. Virol. . 63 . 6 . 2452–6 . 1989 . 2542563 . 10.1128/jvi.63.6.2452-2456.1989. 250699 .
• Kozarsky K, Penman M, Basiripour L . Glycosylation and processing of the human immunodeficiency virus type 1 envelope protein . J. Acquir. Immune Defic. Syndr. . 2 . 2 . 163–9 . 1989 . 2649653 . etal.
• Robinson WE, Montefiori DC, Mitchell WM . Evidence that mannosyl residues are involved in human immunodeficiency virus type 1 (HIV-1) pathogenesis . AIDS Res. Hum. Retroviruses . 3 . 3 . 265–82 . 1988 . 2829950 . 10.1089/aid.1987.3.265 .
• Appert HE, Rutherford TJ, Tarr GE . Isolation of galactosyltransferase from human milk and the determination of its N-terminal amino acid sequence . Biochem. Biophys. Res. Commun. . 138 . 1 . 224–9 . 1986 . 3091013 . 10.1016/0006-291X(86)90269-X . etal. 2027.42/26099 . free .
• Appert HE, Rutherford TJ, Tarr GE . Isolation of a cDNA coding for human galactosyltransferase . Biochem. Biophys. Res. Commun. . 139 . 1 . 163–8 . 1986 . 3094506 . 10.1016/S0006-291X(86)80094-8 . 2027.42/26068 . etal. free .
• Furukawa K, Roth S, Sawicki J . Several Galactosyltransferase Activities Are Associated with Mouse Chromosome 17 . Genetics . 114 . 3 . 983–91 . 1987 . 10.1093/genetics/114.3.983 . 3098628 . 1203025 .
• Masri KA, Appert HE, Fukuda MN . Identification of the full-length coding sequence for human galactosyltransferase (beta-N-acetylglucosaminide: beta 1,4-galactosyltransferase) . Biochem. Biophys. Res. Commun. . 157 . 2 . 657–63 . 1989 . 3144273 . 10.1016/S0006-291X(88)80300-0 .
• Roth J, Lentze MJ, Berger EG . Immunocytochemical demonstration of ecto-galactosyltransferase in absorptive intestinal cells . J. Cell Biol. . 100 . 1 . 118–25 . 1985 . 3917437 . 10.1083/jcb.100.1.118 . 2113462 .
• Roth J, Berger EG . Immunocytochemical localization of galactosyltransferase in HeLa cells: codistribution with thiamine pyrophosphatase in trans-Golgi cisternae . J. Cell Biol. . 93 . 1 . 223–9 . 1982 . 6121819 . 10.1083/jcb.93.1.223 . 2112114 .
• Chatterjee SK, Mukerjee S, Tripathi PK . Analysis of the sequences of human beta-1,4-galactosyltransferase cDNA clones . Int. J. Biochem. Cell Biol. . 27 . 3 . 329–36 . 1995 . 7540104 . 10.1016/1357-2725(94)00062-G .
• Kudo T, Narimatsu H . The beta 1,4-galactosyltransferase gene is post-transcriptionally regulated during differentiation of mouse F9 teratocarcinoma cells . Glycobiology . 5 . 4 . 397–403 . 1995 . 7579794 . 10.1093/glycob/5.4.397 .

External links

• GeneReviews/NCBI/NIH/UW entry on Congenital Disorders of Glycosylation Overview

Notes and References

1. Lo NW, Shaper JH, Pevsner J, Shaper NL . The expanding beta 4-galactosyltransferase gene family: messages from the databanks . Glycobiology . 8 . 5 . 517–26 . Aug 1998 . 9597550 . 10.1093/glycob/8.5.517 .
2. Web site: Entrez Gene: B4GALT1 UDP-Gal:betaGlcNAc beta 1,4- galactosyltransferase, polypeptide 1.