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

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. 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. 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. 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.