Involvement of the <em>Azotobacter vinelandii</em> Rhodanese-Like Protein RhdA in the Glutathione Regeneration Pathway

<div><p>The phenotypic features of the <em>Azotobacter vinelandii</em> RhdA mutant MV474 (in which the <em>rhdA</em> gene was deleted) indicated that defects in antioxidant systems in this organism were related to the expression of the tandem-domain rhodanese RhdA. In this work, further insights on the effects of the oxidative imbalance generated by the absence of RhdA (e.g. increased levels of lipid hydroperoxides) are provided. Starting from the evidence that glutathione was depleted in MV474, and using both <em>in silico</em> and <em>in vitro</em> approaches, here we studied the interaction of wild-type RhdA and Cys²³⁰Ala site-directed RhdA mutant with glutathione species. We found that RhdA was able to bind <em>in vitro</em> reduced glutathione (GSH) and that RhdA-Cys²³⁰ residue was mandatory for the complex formation. RhdA catalyzed glutathione-disulfide formation in the presence of a system generating the glutathione thiyl radical (GS^•, an oxidized form of GSH), thereby facilitating GSH regeneration. This reaction was negligible when the Cys²³⁰Ala RhdA mutant was used. The efficiency of RhdA as catalyst in GS^•-scavenging activity is discussed on the basis of the measured parameters of both interaction with glutathione species and kinetic studies.</p>