B4GALT1

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. [provided by RefSeq, Jul 2008]

Beta-1,4-Galactosyltransferase 1

Beta-1,4-galactosyltransferase 1: 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.
Processed beta-1,4-galactosyltransferase 1: 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.

Acute inflammatory response Source: Ensembl
Angiogenesis involved in wound healing Source: Ensembl
Binding of sperm to zona pellucida Source: Reactome
Cell adhesion Source: Ensembl
Development of secondary sexual characteristics Source: Ensembl
Epithelial cell development Source: Ensembl
Extracellular matrix organization Source: Ensembl
Galactose metabolic process Source: Ensembl
Glycosylation Source: GO_Central
Keratan sulfate biosynthetic process Source: Reactome
Lactose biosynthetic process Source: Reactome
Leukocyte migration Source: Ensembl
Negative regulation of cell population proliferation Source: Ensembl
neutrophil degranulation Source: Reactome
Oligosaccharide biosynthetic process Source: UniProtKB
Penetration of zona pellucida Source: Ensembl
Positive regulation of apoptotic process Source: Ensembl
Positive regulation of epithelial cell proliferation involved in wound healing Source: Ensembl
Protein N-linked glycosylation Source: UniProtKB
Regulation of acrosome reaction Source: Ensembl

Isoform Long: Cell membrane; Golgi stack membrane; Cell surface; Filopodium. Found in trans cisternae of Golgi but is mainly localized at the plasma membrane (PubMed:1714903). B4GALT1 cell surface expression is regulated by UBE2Q1 (By similarity).
Isoform Short: Golgi stack membrane. Found in trans cisternae of Golgi.
Processed beta-1,4-galactosyltransferase 1: Secreted. Soluble form found in body fluids.

Congenital disorder of glycosylation 2D (CDG2D): A multisystem disorder caused by a defect in glycoprotein biosynthesis and characterized by under-glycosylated serum glycoproteins. Congenital disorders of glycosylation result in a wide variety of clinical features, such as defects in 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.

Cytoplasmic: 1-24 aa
Helical: 25-44 aa
Lumenal: 45-398 aa

The soluble form derives from the membrane forms by proteolytic processing.