4ee3 | pdb_00004ee3
Crystal structure of human M340H-beta-1,4-galactosyltransferase-1 (M340H-B4GAL-T1) in complex with pentasaccharide
Structural highlights
DiseaseB4GT1_HUMAN 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. FunctionB4GT1_HUMAN 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. Publication Abstract from PubMedN-acetyllactosamine is the most prevalent disaccharide moiety in the glycans on the surface of mammalian cells and often found as repeat units in the linear and branched polylactosamines, known as i- and I-antigen, respectively. The beta1-4-galactosyltransferase-I (beta4Gal-T1) enzyme is responsible for the synthesis of the N-acetyllactosamine moiety. To understand its oligosaccharide acceptor specificity, we have previously investigated the binding of tri- and pentasaccharides of N-glycan with a GlcNAc at their nonreducing end and found that the extended sugar moiety in these acceptor substrates binds to the crevice present at the acceptor substrate binding site of the beta4Gal-T1 molecule. Here we report seven crystal structures of beta4Gal-T1 in complex with an oligosaccharide acceptor with a nonreducing end GlcNAc that has a beta1-6-glycosidic link and that are analogous to either N-glycan or i/I-antigen. In the crystal structure of the complex of beta4Gal-T1 with I-antigen analog pentasaccharide, the beta1-6-branched GlcNAc moiety is bound to the sugar acceptor binding site of the beta4Gal-T1 molecule in a way similar to the crystal structures described previously; however, the extended linear tetrasaccharide moiety does not interact with the previously found extended sugar binding site on the beta4Gal-T1 molecule. Instead, it interacts with the different hydrophobic surface of the protein molecule formed by the residues Tyr-276, Trp-310, and Phe-356. Results from the present and previous studies suggest that beta4Gal-T1 molecule has two different oligosaccharide binding regions for the binding of the extended oligosaccharide moiety of the acceptor substrate. Binding of N-acetylglucosamine (GlcNAc) beta1-6-branched oligosaccharide acceptors to beta4-galactosyltransferase I reveals a new ligand binding mode.,Ramakrishnan B, Boeggeman E, Qasba PK J Biol Chem. 2012 Aug 17;287(34):28666-74. doi: 10.1074/jbc.M112.373514. Epub, 2012 Jun 27. PMID:22740701[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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