title: How thioredoxin can reduce a buried disulphide bond.
abstract: We present a study of the interaction between thioredoxin and the model enzyme pI258 arsenate reductase (ArsC) from Staphylococcus aureus. ArsC catalyses the reduction of arsenate to arsenite. Three redox active cysteine residues (Cys10, Cys82 and Cys89) are involved. After a single catalytic arsenate reduction event, oxidized ArsC exposes a disulphide bridge between Cys82 and Cys89 on a looped-out redox helix. Thioredoxin converts oxidized ArsC back towards its initial reduced state. In the absence of a reducing environment, the active-site P-loop of ArsC is blocked by the formation of a second disulphide bridge (Cys10-Cys15). While fully reduced ArsC can be recovered by exposing this double oxidized ArsC to thioredoxin, the P-loop disulphide bridge is itself inaccessible to thioredoxin. To reduce this buried Cys10-Cys15 disulphide-bridge in double oxidized ArsC, an intra-molecular Cys10-Cys82 disulphide switch connects the thioredoxin mediated inter-protein thiol-disulphide transfer to the buried disulphide. In the initial step of the reduction mechanism, thioredoxin appears to be selective for oxidized ArsC that requires the redox helix to be looped out for its interaction. The formation of a buried disulphide bridge in the active-site might function as protection against irreversible oxidation of the nucleophilic cysteine, a characteristic that has also been observed in the structurally similar low molecular weight tyrosine phosphatase.
authors.affiliation: Laboratorium voor Ultrastructuur, Vlaams Interuniversitair Instituut voor Biotechnologie (VIB), Vrije Universiteit Brussel, Pleinlaan 2, B-1050 Brussels, Belgium. joris.messens@vub.ac.be
authors.forename: Joris
authors.initials: J
authors.lastname: Messens
authors.forename: Inge
authors.initials: I
authors.lastname: Van Molle
authors.forename: Peter
authors.initials: P
authors.lastname: Vanhaesebrouck
authors.forename: Maya
authors.initials: M
authors.lastname: Limbourg
authors.forename: Karolien
authors.initials: K
authors.lastname: Van Belle
authors.forename: Khadija
authors.initials: K
authors.lastname: Wahni
authors.forename: José C
authors.initials: JC
authors.lastname: Martins
authors.forename: Remy
authors.initials: R
authors.lastname: Loris
authors.forename: Lode
authors.initials: L
authors.lastname: Wyns
mesh_terms: D004220:Disulfides / Q000737:chemistry*; D004591:Electrophoresis, Polyacrylamide Gel; D007700:Kinetics; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D019906:Nuclear Magnetic Resonance, Biomolecular; D010084:Oxidation-Reduction; D011485:Protein Binding; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D013879:Thioredoxins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism
chemical_list: D004220:Disulfides; D013879:Thioredoxins