ATP produced within the mitochondrial matrix through a process termed oxidative phosphorylation (OXPHOS) is transported out of the mitochondria to the rest of the cell via a metabolite carrier proteins termed the ADP/ATP carrier (AAC) family located within the mitochondrial inner membrane (IM). Defects in either the OXPHOS pathway or in the AAC family have been shown to underlie a number of cardiac/muscle myopathies and neurodegenerative diseases. The central focus of this application is the yeast AAC protein family and their physical interaction with components of the OXPHOS complexes, specifically the cytochrome bc1-cytochrome oxidase (COX) supercomplex and the TIM23 protein translocase. Mutations in an AAC isoform found in human cardiac and muscle tissue, the hANT1 protein, is the underlying cause of the disease autosomal-dominant progressive external ophthalmoplegia (adPEO). The onset of adPEO is characterized by a loss of COX activity and modeling of the disease in yeast using the hANT1 ortholog, AAC2, has indicated that it is the structural presence of a mutated AAC family member, rather than a compromised mitochondrial ADP/ATP exchange, which causes the COX biogenesis defect and the subsequent loss of the mitochondrial membrane potential and ultimate cell death. We propose that the further analysis of the physical relationship between the AAC proteins and the cytochrome bc1-COX and TIM23 complexes is essential to understand the molecular pathophysiology of the adPEO disease. We hypothesize the adPEO aac2 mutant proteins may structurally interfere with their associated TIM23 complexes and propose how this may initially cause a defect in the biogenesis of the COX complex and ultimately inhibit the ability of the TIM23 channel to import proteins into the mitochondria, an affect with potentially lethal consequences for the cell. Demonstration of a close physical relationship of the AAC proteins with the TIM23 translocase, a voltage gated channel, may have significant implications not only for our understanding of the adPEO disease, but potentially also for AAC's role in other cellular events such as apoptosis.
The key physiological role played by the mitochondrial ADP/ATP carrier proteins (AAC) is highlighted by the severe disorders that result from their dysfunction or deficiency, such as autosomal-dominant progressive external ophthalmoplegia (adPEO), a disease of adult onset pathology. Evidence to support the association of the AAC proteins with the TIM23 protein translocase and the oxidative phosphorylation (OXPHOS) complex, the cytochrome bc1-COX supercomplex, is presented in this application. We propose that the unexpected and novel finding that AAC can interact with the TIM23 complex, a voltage-gated channel, and the H+pumping OXPHOS complex, has important implications for our understanding of the pathophysiology of diseases and myopathies associated with mutations in the AAC proteins.
| Strogolova, Vera; Furness, Andrew; Robb-McGrath, Micaela et al. (2012) Rcf1 and Rcf2, members of the hypoxia-induced gene 1 protein family, are critical components of the mitochondrial cytochrome bc1-cytochrome c oxidase supercomplex. Mol Cell Biol 32:1363-73 |
