4krv | pdb_00004krv
Crystal structure of catalytic domain of bovine beta1,4-galactosyltransferase mutant M344H-GalT1 complex with 6-sulfo-GlcNAc
Structural highlights
FunctionB4GT1_BOVIN 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 PubMed6-sulfate modified N-acetylglucosamine (6-sulfo-GlcNAc) is often found as part of many biologically important carbohydrate epitopes such as 6-sulfo-LeX. In these epitopes, the 6-sulfo-GlcNAc moiety is extended by a galactose sugar in a beta1-4 linkage. The beta4GalT1 enzyme transfers galactose (Gal) from UDP-Gal to N-acetylglucosamine (GlcNAc) in the presence of manganese. Here we report that the beta4GalT1 enzyme transfers Gal to the 6-sulfo-GlcNAc and 4-methylumbelliferyl-6-sulfo-N-acetyl-beta-D-glucosaminide (6-sulfo-betaGlcNAc-MU) acceptor substrates, although with very low efficiency. To understand the effect that the 6-sulfate group on the GlcNAc acceptor has on the catalytic activity of the beta4GalT1 molecule, we have determined the crystal structure of the catalytic domain of bovine beta4GalT1 mutant enzyme M344H-beta4GalT1 complex with the 6-sulfo-GlcNAc molecule. In the crystal structure, the 6-sulfo-GlcNAc is bound to the protein in a way that is similar to the GlcNAc molecule. However, the 6-sulfate group engages in additional interactions with the hydrophobic region, residues 276-285, of the protein molecule, and this group is found wedged between the aromatic side chains of Phe-280 and Trp314 residues. Since the side chain of the Trp314 residue undergoes conformational changes during the catalytic cycle of the enzyme, molecular interaction between Trp314 and the 6-sulfate group might hinder this conformational change. Therefore, the lack of a favorable binding environment, together with hindrance to the conformational changes, might be responsible for the poor catalytic activity. Investigations on beta1,4-galactosyltransferase I using 6-sulfo-GlcNAc as an acceptor sugar substrate.,Ramakrishnan B, Moncrief AJ, Davis TA, Holland LA, Qasba PK Glycoconj J. 2013 Aug 13. PMID:23942731[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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