title: Glutaredoxin s12: unique properties for redox signaling.
abstract: OBJECTIVE
  Cysteines (Cys) made acidic by the protein environment are generally sensitive to pro-oxidant molecules. Glutathionylation is a post-translational modification that can occur by spontaneous reaction of reduced glutathione (GSH) with oxidized Cys as sulfenic acids (-SOH). The reverse reaction (deglutathionylation) is strongly stimulated by glutaredoxins (Grx) and requires a reductant, often GSH.
  
  
  RESULTS
  Here, we show that chloroplast GrxS12 from poplar efficiently reacts with glutathionylated substrates in a GSH-dependent ping pong mechanism. The pK(a) of GrxS12 catalytic Cys is very low (3.9) and makes GrxS12 itself sensitive to oxidation by H(2)O(2) and to direct glutathionylation by nitrosoglutathione. Glutathionylated-GrxS12 (GrxS12-SSG) is temporarily inactive until it is deglutathionylated by GSH. The equilibrium between GrxS12 and glutathione (E(m(GrxS12-SSG))= -315 mV, pH 7.0) is characterized by K(ox) values of 310 at pH 7.0, as in darkened chloroplasts, and 69 at pH 7.9, as in illuminated chloroplasts.
  
  
  METHODS
  Based on thermodynamic data, GrxS12-SSG is predicted to accumulate in vivo under conditions of mild oxidation of the GSH pool that may occur under stress. Moreover, GrxS12-SSG is predicted to be more stable in chloroplasts in the dark than in the light.
  
  
  CONCLUSIONS
  These peculiar catalytic and thermodynamic properties could allow GrxS12 to act as a stress-related redox sensor, thus allowing glutathione to play a signaling role through glutathionylation of GrxS12 target proteins.
authors.affiliation: Laboratoire de Biologie Moléculaire et Cellulaire des Eucaryotes, FRE3354 Centre National de la Recherche Scientifique, Institut de Biologie Physico-Chimique, Université Pierre et Marie Curies, Paris, France.
authors.forename: Mirko
authors.initials: M
authors.lastname: Zaffagnini
authors.forename: Mariette
authors.initials: M
authors.lastname: Bedhomme
authors.forename: Christophe H
authors.initials: CH
authors.lastname: Marchand
authors.forename: J R My
authors.initials: JR
authors.lastname: Couturier
authors.forename: Xing-Huang
authors.initials: XH
authors.lastname: Gao
authors.forename: Nicolas
authors.initials: N
authors.lastname: Rouhier
authors.forename: Paolo
authors.initials: P
authors.lastname: Trost
authors.forename: St Phane D
authors.initials: SP
authors.lastname: Lemaire
mesh_terms: D000478:Alkylation; D019943:Amino Acid Substitution; D002384:Catalysis; D020134:Catalytic Domain; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D054477:Glutaredoxins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007460:Iodoacetamide / Q000494:pharmacology; D007700:Kinetics; D010084:Oxidation-Reduction; D032107:Populus / Q000201:enzymology; D015398:Signal Transduction; D013379:Substrate Specificity
chemical_list: D004791:Enzyme Inhibitors; D054477:Glutaredoxins; D007460:Iodoacetamide