title: Identification of an allosteric anion-binding site on O-acetylserine sulfhydrylase: structure of the enzyme with chloride bound.
abstract: A new crystal structure of O-acetylserine sulfhydrylase (OASS) has been solved with chloride bound at an allosteric site and sulfate bound at the active site. The bound anions result in a new "inhibited" conformation, that differs from the "open" native or "closed" external aldimine conformations. The allosteric site is located at the OASS dimer interface. The new inhibited structure involves a change in the position of the "moveable domain" (residues 87-131) to a location that differs from that in the open or closed forms. Formation of the external aldimine with substrate is stabilized by interaction of the alpha-carboxyl group of the substrate with a substrate-binding loop that is part of the moveable domain. The inhibited conformation prevents the substrate-binding loop from interacting with the alpha-carboxyl group, and hinders formation of the external Schiff base and thus subsequent chemistry. Chloride may be an analog of sulfide, the physiological inhibitor. Finally, these results suggest that OASS represents a new class of PLP-dependent enzymes that is regulated by small anions.
authors.affiliation: M.E. Müller Institute for Structural Biology. Peter.Burkhard@unibas.ch
authors.forename: P
authors.initials: P
authors.lastname: Burkhard
authors.forename: C H
authors.initials: CH
authors.lastname: Tai
authors.forename: J N
authors.initials: JN
authors.lastname: Jansonius
authors.forename: P F
authors.initials: PF
authors.lastname: Cook
mesh_terms: D000494:Allosteric Regulation; D000495:Allosteric Site; D000838:Anions / Q000378:metabolism / Q000494:pharmacology; D002712:Chlorides / Q000378:metabolism* / Q000494:pharmacology; D018360:Crystallography, X-Ray; D003545:Cysteine / Q000096:biosynthesis / Q000378:metabolism; D003547:Cysteine Synthase / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000378:metabolism*; D019281:Dimerization; D006860:Hydrogen Bonding; D008958:Models, Molecular; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011732:Pyridoxal Phosphate / Q000378:metabolism; D012486:Salmonella typhimurium / Q000201:enzymology* / Q000378:metabolism; D013329:Structure-Activity Relationship; D013431:Sulfates / Q000378:metabolism; D013440:Sulfides / Q000378:metabolism
chemical_list: D000838:Anions; D002712:Chlorides; D013431:Sulfates; D013440:Sulfides; D011732:Pyridoxal Phosphate; D003547:Cysteine Synthase; D003545:Cysteine