title: Exploration of the active site of β4GalT7: modifications of the aglycon of aromatic xylosides.
abstract: Proteoglycans (PGs) are macromolecules that consist of long linear polysaccharides, glycosaminoglycan (GAG) chains, covalently attached to a core protein by the carbohydrate xylose. The biosynthesis of GAG chains is initiated by xylosylation of the core protein followed by galactosylation by the galactosyltransferase β4GalT7. Some β-d-xylosides, such as 2-naphthyl β-d-xylopyranoside, can induce GAG synthesis by serving as acceptor substrates for β4GalT7 and by that also compete with the GAG synthesis on core proteins. Here we present structure-activity relationships for β4GalT7 and xylosides with modifications of the aromatic aglycon, using enzymatic assays, cell studies, and molecular docking simulations. The results show that the aglycons reside on the outside of the active site of the enzyme and that quite bulky aglycons are accepted. By separating the aromatic aglycon from the xylose moiety by linkers, a trend towards increased galactosylation with increased linker length is observed. The galactosylation is influenced by the identity and position of substituents in the aromatic framework, and generally, only xylosides with β-glycosidic linkages function as good substrates for β4GalT7. We also show that the galactosylation ability of a xyloside is increased by replacing the anomeric oxygen with sulfur, but decreased by replacing it with carbon. Finally, we propose that reaction kinetics of galactosylation by β4GalT7 is dependent on subtle differences in orientation of the xylose moiety.
authors: Center for Analysis and Synthesis, Center for Chemistry and Chemical Engineering, Lund University, P.O. Box 124, SE-221 00 Lund, Sweden. ulf.ellervik@chem.lu.se.
authors: Anna
authors: A
authors: Siegbahn
authors: Karin
authors: K
authors: Thorsheim
authors: Jonas
authors: J
authors: Ståhle
authors: Sophie
authors: S
authors: Manner
authors: Christoffer
authors: C
authors: Hamark
authors: Andrea
authors: A
authors: Persson
authors: Emil
authors: E
authors: Tykesson
authors: Katrin
authors: K
authors: Mani
authors: Gunilla
authors: G
authors: Westergren-Thorsson
authors: Göran
authors: G
authors: Widmalm
authors: Ulf
authors: U
authors: Ellervik
mesh_terms: D000438:Alcohols / Q000737:chemistry*; D020134:Catalytic Domain; D005700:Galactosyltransferases / Q000737:chemistry / Q000378:metabolism*; D006027:Glycosides / Q000138:chemical synthesis / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D062105:Molecular Docking Simulation; D014407:Tumor Cells, Cultured
chemical_list: D000438:Alcohols; D006027:Glycosides; C010807:xylosides; D005700:Galactosyltransferases