Aim32, a dual‐localized 2Fe‐2S mitochondrial protein that functions in redox quality control

Abstract

Maintaining redox homeostasis under normal and stress conditions in the mitochondrion is complex. Yeast being a facultative anaerobe, likely uses diverse electron acceptors to sustain the redox-dependent mitochondrial intermembrane space assembly (MIA) pathway under different environmental conditions. We used mass spectrometry in an effort to identify additional proteins that interacted with the sulfhydryl oxidase Erv1 of the MIA pathway. Aim32, a thioredoxin-like [2Fe-2S] ferredoxin protein, was identified as an Erv1 binding protein. Detailed and complementary localization studies showed that Aim32 resided in both the mitochondrial matrix and intermembrane space, placing it in a rare protein class that is dual-localized within mitochondria. Aim32 interacted with additional proteins including redox protein Osm1 as well as protein import components Tim17, Tim23, and Tim22. Deletion of Aim32 or conserved cysteine residues that coordinate the Fe-S center resulted in an increased accumulation of proteins with aberrant disulfide linkages. In addition, the steady-state level of assembled TIM22, TIM23, and Oxa1 protein import complexes was decreased and a subset of the import complexes showed misassembly, among other phenotypes. Aim32 also bound to several mitochondrial proteins under non-reducing conditions, suggesting a function in maintaining the redox status of oxidized proteins by potentially targeting cysteine residues that may be sensitive to oxidation. Finally, Aim32 was essential for growth in conditions of stress, and upon challenge with hydroxyurea (HU). This is the first evidence of the Fe-S protein, Aim32 being uniquely localized to both the mitochondrial intermembrane space and matrix with a role in redox regulation.