The Arabidopsis Mitochondrial Glutaredoxin GRXS15 Provides [2Fe-2S] Clusters for ISCA-Mediated [4Fe-4S] Cluster Maturation |
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Authors: | Tamanna Azam Jonathan Przybyla-Toscano Florence Vignols Jrmy Couturier Nicolas Rouhier Michael K Johnson |
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Affiliation: | 1.Department of Chemistry and Center for Metalloenzyme Studies, University of Georgia, Athens, GA 30602, USA;2.Université de Lorraine, INRAE, IAM, F-54000 Nancy, France; (J.P.-T.); (J.C.); (N.R.);3.BPMP, Université de Montpellier, CNRS, INRAE, SupAgro, 34060 Montpellier, France; |
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Abstract: | Iron-sulfur (Fe-S) proteins are crucial for many cellular functions, particularly those involving electron transfer and metabolic reactions. An essential monothiol glutaredoxin GRXS15 plays a key role in the maturation of plant mitochondrial Fe-S proteins. However, its specific molecular function is not clear, and may be different from that of the better characterized yeast and human orthologs, based on known properties. Hence, we report here a detailed characterization of the interactions between Arabidopsis thaliana GRXS15 and ISCA proteins using both in vivo and in vitro approaches. Yeast two-hybrid and bimolecular fluorescence complementation experiments demonstrated that GRXS15 interacts with each of the three plant mitochondrial ISCA1a/1b/2 proteins. UV-visible absorption/CD and resonance Raman spectroscopy demonstrated that coexpression of ISCA1a and ISCA2 resulted in samples with one 2Fe-2S]2+ cluster per ISCA1a/2 heterodimer, but cluster reconstitution using as-purified 2Fe-2S]-ISCA1a/2 resulted in a 4Fe-4S]2+ cluster-bound ISCA1a/2 heterodimer. Cluster transfer reactions monitored by UV-visible absorption and CD spectroscopy demonstrated that 2Fe-2S]-GRXS15 mediates 2Fe-2S]2+ cluster assembly on mitochondrial ferredoxin and 4Fe-4S]2+ cluster assembly on the ISCA1a/2 heterodimer in the presence of excess glutathione. This suggests that ISCA1a/2 is an assembler of 4Fe-4S]2+ clusters, via two-electron reductive coupling of two 2Fe-2S]2+ clusters. Overall, the results provide new insights into the roles of GRXS15 and ISCA1a/2 in effecting 2Fe-2S]2+ to 4Fe-4S]2+ cluster conversions for the maturation of client 4Fe-4S] cluster-containing proteins in plants. |
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Keywords: | mitochondria iron-sulfur protein Arabidopsis thaliana protein-protein interaction circular dichroism Raman spectroscopy iron-sulfur cluster trafficking glutaredoxin ISCA proteins |
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