B4GALT7

Beta-1,4-galactosyltransferase 7 also known as galactosyltransferase I is an is_associated_with::enzyme that in humans is encoded by the B4GALT7 is_associated_with::gene. Galactosyltransferase I catalyzes the synthesis of the is_associated_with::glycosaminoglycan-protein linkage in is_associated_with::proteoglycans. Proteoglycans in turn are structural components of the is_associated_with::extracellular matrix that is found between cells in is_associated_with::connective tissues.

Function
Galactosyltransferase I is one of seven β-1,4-is_associated_with::galactosyltransferase (β4GalT) enyzmes. These enzymes are type II membrane-bound is_associated_with::glycoproteins that appear to have exclusive specificity for the donor substrate is_associated_with::UDP-galactose; all transfer galactose in a β-1,4 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 is_associated_with::hydrophobic signal sequence that directs the protein to the is_associated_with::Golgi apparatus and which then remains uncleaved to function as a transmembrane anchor. By sequence similarity, the beta4GalTs form four groups: β4GalT1 and β4GalT2, β4GalT3 and β4GalT4, β4GalT5 and β4GalT6, and β4GalT7. The enzyme encoded by this gene attaches the first galactose in the common carbohydrate-protein (GlcA-β-1,3-Gal-β-1,3-Gal-β-1,4-Xyl-beta1-O-Ser) linkage found in is_associated_with::proteoglycans. is_associated_with::Manganese is required as a cofactor. This enzyme differs from the other six beta4GalTs because it lacks the conserved β4GalT1-β4GalT6 Cys residues and it is located in cis-Golgi instead of trans-Golgi.

Clinical significance
Mutations in the B4GALT7 gene that result in a defective galactosyltransferase I enzyme with reduced or absent activity are associated with progeroid type is_associated_with::Ehlers-Danlos syndrome. Since mutations in B4GALT7 impair a glycosylation pathway, the resulting subtype of is_associated_with::Ehlers-Danlos syndrome may be considered a is_associated_with::congenital disorder of glycosylation (CDG), according to the new CDG nomenclature.

Mutations in B4GALT7 cause Larsen syndrome.