Assessing the properties of the mitochondrial respiratory chain organization by controllin the formation of supercomplexes
Abstract
Biogenesis and function of the mitochondrial respiratory chain (MRC) involve the dynamic organization of the single MRC enzymes in ordered structures known as supercomplexes or respirasomes. It is currently accepted that, in the mitochondrial inner membrane, freely diffusing individual MRC enzymes co-exist with supercomplexes of different compositions. However, very little is known regarding the mechanisms that determine MRC organization and regulate its dynamics in response to the cellular metabolic requirements. Notably, this organization is altered in a variety of human mitochondrial disorders caused by mutations in both mitochondrial and nuclear genes. The disease biochemical phenotype frequently includes alterations in supercomplex organization, but their contribution to pathology and mitochondrial dysfunction is unclear. A growing number of observations suggest that MRC supercomplexes may offer structural and functional advantages to the system. However, although several hypotheses have been proposed, the functional significance of the supercomplexes remains to be fully elucidated. Following the recent availability of structures of respiratory supercomplexes, it is now timely to precisely understand the contribution of these macrostructures to mitochondrial physiology. To achieve this goal, we are using the unicellular yeast Saccharomyces cerevisiae, where only a limited number of supercomplexes accumulate (CIII2+CIV1-2) due to the absence of multimeric complex I. Our approach is based on the analysis of two classes of bioengineered strains, designed to fully control supercomplex formation. First, in a set of strains, by expressing a complex III subunit covalently linked to a complex IV subunit, we have forced the generation of tethered supercomplexes with enhanced interactions between MRC enzymes, and the virtual absence of individual complexes. Second, we constructed strains expressing functional variants of the complex III subunit Cor1 that impair supercomplex association without altering the individual MRC complexes. Biochemical and physiological studies on these tightly controlled systems, in which supercomplex formation is the only variable, will allow us to test the proposed supercomplex properties in health and disease, in the absence of confounding factors. These properties include electron transfer efficiency and the minimization of ROS production, and supercomplex modulation of energy output in response to cellular energetic demands. We anticipate that the completion of the proposed studies will impact both our fundamental knowledge of the MRC organization and the understanding of the pathogenic mechanisms underlying MRC deficiencies in human mitochondrial disorders.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Oct 07, 2021
- Source ID
- W911NF2110359
Entities
People
- Flavia Fontanesi
Organizations
- Army Contracting Command
- United States Army
- University of Miami