Characterization of the evolutionarily conserved iron-sulfur cluster of sirohydrochlorin ferrochelatase from Arabidopsis thaliana

Saha, Kaushik, Webb, Michael E., Rigby, Stephen E.J., Leech, Helen K., Warren, Martin J. ORCID: https://orcid.org/0000-0002-6028-6456 and Smith, Alison G. (2012) Characterization of the evolutionarily conserved iron-sulfur cluster of sirohydrochlorin ferrochelatase from Arabidopsis thaliana. Biochemical Journal, 444 (2). pp. 227-237. ISSN 0264-6021

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Abstract

Sirohaem is a cofactor of nitrite and sulfite reductases, essential for assimilation of nitrogen and sulfur. Sirohaem is synthesized from the central tetrapyrrole intermediate uroporphyrinogen III by methylation, oxidation and ferrochelation reactions. In Arabidopsis thaliana, the ferrochelation step is catalysed by sirohydrochlorin ferrochelatase (SirB), which, unlike its counterparts in bacteria, contains an [Fe-S] cluster. We determined the cluster to be a [4Fe-4S] type, which quickly oxidizes to a [2Fe-2S] form in the presence of oxygen. We also identified the cluster ligands as four conserved cysteine residues located at the C-terminus. A fifth conserved cysteine residue, Cys 135, is not involved in ligating the cluster directly, but influences the oxygen-sensitivity of the [4Fe-4S] form, and possibly the affinity for the substrate metal. Substitution mutants of the enzyme lacking the Fe-S cluster or Cys135 retain the same specific activity in vitro and dimeric quaternary structure as the wild-type enzyme. The mutant variants also rescue a defined Escherichia coli sirohaem-deficient mutant. However, the mutant enzymes cannot complement Arabidopsis plants with a null AtSirB mutation, which exhibits post-germination arrest. These observations suggest an important physiological role for the Fe-S cluster in planta, highlighting the close association of iron, sulfur and tetrapyrrole metabolism.

Item Type: Article
Uncontrolled Keywords: arabidopsis thaliana,enhancer-trap line,functional complementation,iron-sulfur cluster,post-germination arrest,sirohaem,biochemistry,molecular biology,cell biology ,/dk/atira/pure/subjectarea/asjc/1300/1303
Faculty \ School: Faculty of Science
Faculty of Science > School of Biological Sciences
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Depositing User: LivePure Connector
Date Deposited: 20 Sep 2022 15:30
Last Modified: 27 Sep 2022 08:37
URI: https://ueaeprints.uea.ac.uk/id/eprint/88511
DOI: 10.1042/BJ20111993

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