Investigating the role of the human CIA2A-CIAO1 complex in the maturation of aconitase

Background: The CIA2A protein, in complex with CIAO1, has been proposed to be exclusively implicated in the maturation of cytosolic aconitase. However, how the CIA2A-CIAO1 complex generates active aconitase is still unknown and the available structural information has not provided any crucial insights into the molecular function of CIA2A. Methods: In this work we have characterized the Fe/S cluster binding properties of CIA2A and of the CIA2A-CIAO1 complex via NMR, UV - vis absorption and EPR spectroscopies and we have investigated how the Fe/S cluster is transferred to inactive aconitase/IRP1 protein. Results: We found that an heterotrimeric species formed by two molecules of CIA2A and one of CIAO1 can bind one [4Fe-4S] cluster and that residue Cys90 of CIA2A is one of the cluster ligand. The holo trimeric complex is able to transfer the [4Fe-4S] cluster to apo-IRP1 thus generating the active form of aconitase. Conclusions and general significance: These findings, which highlight a functional role for CIA2A-CIAO1 complex in aconitase maturation, raises a broad interest and can have a high impact on the community studying metal trafficking and iron-sulfur protein biogenesis. The present study can provide solid bases for further investigation of the molecular mechanisms involving also other CIA machinery proteins.