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Perception du stress métallique (nickel/cobalt) par le système de signalisation transmembranaire Cnr chez Cupriavidus metallidurans CH34

Abstract : CnrX is the membrane-anchored periplasmic sensor of the CnrYXH complex that contributes to regulate the expression of the genes involved in cobalt and nickel resistance in Cupriavidus metallidurans CH34. This resistance is induced by the release of the ExtraCytoplasmic Function (ECF) sigma factor CnrH from the CnrYX complex upon sensing of Ni or Co. We addressed the metal sensing mechanisms of CnrXs, the strategies used to select Ni or Co and the nature of the signal onset. Biophysical and spectroscopic techniques allowed us to study the metal binding sites in solution. The CnrXs dimer contains four cobalt binding sites. Two (F sites) are present in the full-length protein which H32A-CnrXs mutant is an excellent model of. The two other sites have an unusual spectroscopic signal that might be due to the formation of a binuclear cobalt complex. We present also high-resolution structures of CnrXs in the apo, Ni-, Co-, and Zn-bound forms. We propose that Zn-bound CnrX typifies the resting state of the complex and that the sensing mechanism is triggered by the substitution of Zn for Ni or Co in the F site. This substitution leads to dramatic changes in the metal-binding site. While the Zn ion is pentacoordinated in a 3N2O sphere, Ni or Co ions recruit the thioether sulfur of the only methionine (Met123) residue as a sixth ligand to form an octahedral site. We propose that the Met123 side chain recruitment is the qualitative change that switches on the sensing mechanism by remodeling the four-helix bundle that accommodates the metal-binding site. To our knowledge these results represent the first structural and spectroscopic study of a periplasmic metal sensor involved in transmembrane signal transduction for the activation of an ECF-type sigma factor.
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Submitted on : Tuesday, January 3, 2012 - 3:47:46 PM
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  • HAL Id : tel-00656119, version 1



Juliette Trepreau. Perception du stress métallique (nickel/cobalt) par le système de signalisation transmembranaire Cnr chez Cupriavidus metallidurans CH34. Autre [q-bio.OT]. Université de Grenoble, 2011. Français. ⟨NNT : 2011GRENV061⟩. ⟨tel-00656119⟩



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