B4GALT1

Beta1,4-Galactosyltransferase-I (B4GALT1), one of seven beta1,4-galactosyltransferases, is an enzyme commonly found in the trans-Golgi complex that adds galactose to oligosaccharides. 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. B4GALT1 gene directs production of B4GALT1 protein using either of two transcription start sites. The product of the smaller transcript serves the traditional biosynthetic role in the Golgi. This form also complexes with α-lactalbumin, a mammary-specific protein, to form lactose synthase. In addition to a biosynthetic role, the protein translated from the longer transcript appears on the plasma membranes of some cells where it serves as a signalling receptor in cell-matrix interactions such as sperm-egg binding.

B4GALT1 Related Areas

Enzyme>>Carbohydrate Metabolism Enzymes>>B4GALT1

B4GALT1 Alternative Names

B4GALT1, B4GAL-T1, GGTB2, beta4Gal-T1, DKFZp686N19253, GT1, GTB, MGC50983 [Homo sapiens]

B4GALT1, Ggtb2, Ggtb, B-1,4-GalT, RP23-135L5.6, AA407245, GalT [Mus musculus]

Summaries for B4GALT1

Entrez Gene summary for B4GALT1:

This B4GALT1 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 B4GALT1 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. [provided by RefSeq, Jul 2008]

OMIM - description for B4GALT1:

The enzyme galactosyltransferase (EC 2.4.1.38) catalyzes the reaction involving UDP-galactose and N-acetylglucosamine for the production of galactose beta-1,4-N-acetylglucosamine. The galactosyltransferase enzyme can also form a heterodimer with the regulatory protein alpha-lactalbumin to form lactose synthetase (EC 2.4.1.22). In addition to a biosynthetic role, galactosyltransferases may be components of plasma membranes where they may function in intercellular recognition and/or adhesion. Masri et al. (1988) noted that galactosyltransferase, which they called beta-1,4-galactosyltransferase, is located primarily in the trans-cisternae of the Golgi complex and exists in both membrane-bound and soluble forms.

Wikipedia summary for B4GALT1:

Beta-1,4-galactosyltransferase 1 is an enzyme that in humans is encoded by the B4GALT1 gene.

Human B4GALT1 Protein General Information

 

• Protein names: Beta-1,4-galactosyltransferase 1, Short name=b4Gal-T1
• Sequence length: 398 AA.
• Catalytic activity: UDP-galactose + D-glucose = UDP + lactose.
  UDP-galactose + N-acetyl-beta-D-glucosaminylglycopeptide = UDP + beta-D-galactosyl-(1->4)-N-acetyl-beta-D-glucosaminylglycopeptide.
  UDP-galactose + N-acetyl-D-glucosamine = UDP + N-acetyllactosamine.
• Cofactor: Manganese
• Pathway: Protein modification; protein glycosylation.
• Sequence similarities: B4GALT1 belongs to the glycosyltransferase 7 family.
• Post-translational modification: The soluble form derives from the membrane forms by proteolytic processing.
• Subunit structure: Homodimer; and heterodimer with alpha-lactabulmin to form lactose synthase.
• Subcellular location: Isoform Long: Golgi apparatus › Golgi stack membrane; Single-pass type II membrane protein. Cell membrane; Single-pass type II membrane protein. Cell surface. Note: Found in trans cisternae of Golgi.
  Isoform Short: Golgi apparatus › Golgi stack membrane; Single-pass type II membrane protein. Note: Found in trans cisternae of Golgi.
  Processed beta-1,4-galactosyltransferase 1: Secreted. Note: Soluble form found in body fluids.
• Tissue specificity: B4GALT1 is ubiquitously expressed, but at very low levels in fetal and adult brain.
• Involvement in disease: Defects in B4GALT1 are the cause of congenital disorder of glycosylation type 2D (CDG2D) [MIM:607091]. CDGs are a family of severe inherited diseases caused by a defect in protein N-glycosylation. They are characterized by under-glycosylated serum proteins. These multisystem disorders present with a wide variety of clinical features, such as disorders of the nervous system development, psychomotor retardation, dysmorphic features, hypotonia, coagulation disorders, and immunodeficiency. The broad spectrum of features reflects the critical role of N-glycoproteins during embryonic development, differentiation, and maintenance of cell functions.

General information above from UniProt

Function for B4GALT1 Protein

UniProtKB:

The Golgi complex form catalyzes the production of lactose in the lactating mammary gland and could also be responsible for the synthesis of complex-type N-linked oligosaccharides in many glycoproteins as well as the carbohydrate moieties of glycolipids.
The cell surface form functions as a recognition molecule during a variety of cell to cell and cell to matrix interactions, as those occurring during development and egg fertilization, by binding to specific oligosaccharide ligands on opposing cells or in the extracellular matrix.

Genatlas:

• lactose synthetase
• involved in lactose biosynthesis and glyco conjugates in absence of alpha-lactalbulmin

Phenotype Information for B4GALT1

• Gene/Locus: B4GALT1, GGTB2, GT1, GTB, CDG2D
• Phenotype: Congenital disorder of glycosylation, type IId

Phenotype Information for B4GALT1 from OMIM (Online Mendelian Inheritance in Man)