IBA57 Recruits ISCA2 to Form a [2Fe-2S] Cluster-Mediated Complex

Area of Science:

• Mitochondrial biology
• Protein biochemistry
• Cellular metabolism

Background:

• Mitochondrial iron-sulfur (Fe-S) proteins are essential for numerous cellular processes.
• The maturation of these proteins relies on a complex machinery, with IBA57 implicated in a late stage.
• The precise molecular interactions within this machinery remain unclear.

Purpose of the Study:

• To elucidate the molecular mechanism of human IBA57 protein function in mitochondrial Fe-S protein biogenesis.
• To define the role of IBA57 in complex formation with other ISC machinery components.
• To investigate the functional consequences of IBA57-ISCA2 complex formation.

Main Methods:

• Heterodimerization assays to study protein complex formation.
• Site-directed mutagenesis to identify critical amino acid residues (cysteines) involved in cluster binding.
• In vitro assays to assess the activity of the formed complex, including apo-aconitase reactivation.

Main Results:

• Human IBA57 forms a stable heterodimeric complex with ISCA2, mediated by a bridging [2Fe-2S] cluster.
• [2Fe-2S] cluster binding is essential for the formation of the IBA57-ISCA2 complex.
• Specific cysteines in both IBA57 and ISCA2 act as ligands for the [2Fe-2S] cluster.
• The resulting [2Fe-2S] ISCA2-IBA57 complex is stable and can reactivate apo-aconitase in vitro.

Conclusions:

• A [2Fe-2S] cluster transfer pathway involving GLRX5, ISCA2, and IBA57 has been delineated.
• The final step involves the formation of a stable [2Fe-2S] ISCA2-IBA57 complex, essential for Fe-S protein maturation.
• This complex plays a critical role in ensuring the proper function of mitochondrial Fe-S proteins.