Molecular characterization of a complex of apoptosis-inducing factor 1 with cytochrome c oxidase of the mitochondrial respiratory chain

Abstract

Combining mass spectrometry–based chemical cross-linking and complexome profiling, we analyzed the interactome of heart mitochondria. We focused on complexes of oxidative phosphorylation and found that dimeric apoptosis-inducing factor 1 (AIFM1) forms a defined complex with ∼10% of monomeric cytochrome c oxidase (COX) but hardly interacts with respiratory chain supercomplexes. Multiple AIFM1 intercross-links engaging six different COX subunits provided structural restraints to build a detailed atomic model of the COX-AIFM12 complex (PDBDEV_00000092). An application of two complementary proteomic approaches thus provided unexpected insight into the macromolecular organization of the mitochondrial complexome. Our structural model excludes direct electron transfer between AIFM1 and COX. Notably, however, the binding site of cytochrome c remains accessible, allowing formation of a ternary complex. The discovery of the previously overlooked COX-AIFM12 complex and clues provided by the structural model hint at potential roles of AIFM1 in oxidative phosphorylation biogenesis and in programmed cell death.

CG7630 is the Drosophila melanogaster homolog of the cytochrome c oxidase subunit COX7B

“…Consistent with the intermembrane space location of the AIF protein (Otera et al , 2005 ), the gene is fused with the C‐terminus of the CG7630 homolog, which is predicted to be in the intermembrane space. Remarkably, a very recent work showed that around 10% of mammalian COX interacts with AIF (Hevler et al , 2021 ). Our findings support the hypothesis that the fusion protein formed by the ortholog of CG7630+AIF, detected in some protostomes, has a functional role, which is carried out in deuterostomes by COX7B interacting with, but physically separated from AIF.…”

Complexome Profiling—Exploring Mitochondrial Protein Complexes in Health and Disease

“…Cross-linking mass spectrometry (XL-MS) has emerged as a powerful technology for interactome and structural biology studies in mitochondria ( Schweppe et al, 2017 ; Liu et al, 2018 ; Ryl et al, 2020 ; Hevler et al, 2021b ). Chemical cross-linkers react covalently with residues of proteins that are in close proximity to stabilize native PPIs for further characterization ( Gomes and Gozzo, 2010 ; Mintseris and Gygi, 2020 ).…”

“…It has lately been demonstrated that CP and XL-MS are highly complementary and could provide valuable insights into the macromolecular organization of, for instance, the mitochondrial complexome. By combining CP and XL-MS data, Hevler and co-workers build a detailed atomic model of bovine CIV associated with dimeric apoptosis-inducing factor 1 (AIFM1) ( Hevler et al, 2021b ). CP analysis was indeed helpful to determine the stoichiometry of such a complex and validating this interaction.…”

Mechanisms of Survival of Cytomegalovirus-Infected Tumor Cells

“…The apoptosis-inducing factor (AIF) is another proapoptotic factor released from mitochondria and acts as a main effector of its own apoptosis pathway. AIF triggers the apoptosis-related reactions in a caspase-independent manner, and, consequently, its apoptosis pathway is also known as the caspase-independent pathway [ 58 ].…”