title: The structural basis for a coordinated reaction catalyzed by a bifunctional glycosyltransferase in chondroitin biosynthesis.
abstract: Bifunctional chondroitin synthase K4CP catalyzes glucuronic acid and N-acetylgalactosamine transfer activities and polymerizes a chondroitin chain. Here we have determined that an N-terminal region (residues 58-134) coordinates two transfer reactions and enables K4CP to catalyze polymerization. When residues 58-107 are deleted, K4CP loses polymerase activity while retaining both transfer activities. Peptide (113)DWPSDL(118) within this N-terminal region interacts with C-terminal peptide (677)YTWEKI(682). The deletion of either sequence abolishes glucuronic acid but not N-acetylgalactosamine transfer activity in K4CP. Both donor bindings and transfer activities are lost by mutating (677)YTWEKI(682) to (677)DAWEDI(682). On the other hand, acceptor substrates retain their binding to K4CP mutants. The characteristics of these K4CP mutants highlight different states of the enzyme reaction, providing an underlying structural basis for how these peptides play essential roles in coordinating the two glycosyltransferase activities for K4CP to elongate the chondroitin chain.
authors.affiliation: Pharmacogenetics Section, Laboratory of Reproductive and Developmental Toxicology, NIEHS, National Institutes of Health, Research Triangle Park, North Carolina 27709, USA.
authors.forename: Mack
authors.initials: M
authors.lastname: Sobhany
authors.forename: Yoshimitsu
authors.initials: Y
authors.lastname: Kakuta
authors.forename: Nobuo
authors.initials: N
authors.lastname: Sugiura
authors.forename: Koji
authors.initials: K
authors.lastname: Kimata
authors.forename: Masahiko
authors.initials: M
authors.lastname: Negishi
mesh_terms: D020816:Amino Acid Motifs; D002384:Catalysis; D002807:Chondroitin / Q000096:biosynthesis / Q000737:chemistry* / Q000235:genetics; D004926:Escherichia coli / Q000201:enzymology* / Q000235:genetics; D006031:Glycosylation; D006602:Hexosyltransferases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D009154:Mutation; D010455:Peptides / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D017434:Protein Structure, Tertiary; D013329:Structure-Activity Relationship
chemical_list: D010455:Peptides; D002807:Chondroitin; D006602:Hexosyltransferases; C460368:chondroitin polymerase, E coli