CIAO3 protein forms a stable ternary complex with two key players of the human cytosolic iron–sulfur cluster assembly machinery


The CIAO3 protein operates at a crossroad of the cytosolic iron–sulfur protein assembly (CIA) machinery. Although the functional role of CIAO3 has been recently characterized, a description of its interaction network is still not complete. Literature data suggested that CIAO3 interacts individually with CIA2A and CIAO1 protein, with the latter two interacting each other. However, no experimental data are available yet showing the formation of a possible ternary complex composed by CIAO3, CIAO1, and CIA2A. This work shows, for the first time, via size exclusion chromatography coupled with multiangle light scattering, UV–vis absorption and electron paramagnetic resonance (EPR) spectroscopies, the formation of a stable, [4Fe-4S]-bound, complex, composed by CIAO3 and the hetero-CIA2A–CIAO1 complex. Moreover, site-directed mutagenesis data suggested a structural role for the C-terminal [4Fe-4S] cluster of the CIAO3 protein. These findings can provide solid bases for further investigation of the molecular mechanisms involving these CIA machinery proteins.

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Iron regulatory protein 1


Cytosolic iron–sulfur protein assembly


Electron paramagnetic resonance


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We thank Dr. A. Bonucci (CERM) for assistance in recording the EPR spectra. This work was supported by Fondazione Cassa di Risparmio di Firenze project title “Dalla Struttura tridimensionale di antigeni proteici all’ottimizzazione di potenziali candidati vaccini” and by Instruct-ERIC, a Landmark ESFRI project, and specifically, we thank the CERM/CIRMMP Italy Centre. Financial support was also provided by European EC Horizon2020 TIMB3 (Project 810856).

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Correspondence to Francesca Cantini or Lucia Banci.

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Maione, V., Grifagni, D., Torricella, F. et al. CIAO3 protein forms a stable ternary complex with two key players of the human cytosolic iron–sulfur cluster assembly machinery. J Biol Inorg Chem 25, 501–508 (2020).

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  • Iron–sulfur protein
  • CIAO3
  • IOP1
  • CIA2A
  • CIAO1
  • CIA machinery
  • EPR