Functional characterization of mitochondrial supercomplexes

• Applicant: Etienne Meyer, Ph.D.
• Subject Area: Plant Biochemistry and Biophysics ; Plant Physiology
• Term: from 2019 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 428658830

In the project ‘Control of complex I proteostasis in plants’, we proposed to study uncharacterized mitochondrial proteins, identified in a bioinformatic screen, as candidates involved in complex I proteostasis. We have characterized two proteins important for the assembly of the membrane arm of complex I. We also investigated the role of a small mitochondrial protein family in the regulation of the assembly of several complexes of the Oxidative Phosphorylation (OXPHOS) system. Finally, we have identified a new isoform of a subunit of the mitochondrial ATP synthase. Interestingly, the analysis of the organization of the OXPHOS complexes in knock-out mutants for some of these proteins show that OXPHOS supercomplexes cannot be formed. Supercomplexes are stoichiometric higher-order assemblies of two of more OXPHOS complexes. Despite their ubiquitous presence in all organisms investigated and the growing number of supercomplex structures obtained recently, their function is still unresolved. It has been suggested that they might play an important role in the structural organization of the cristae or that they are improving the efficiency of the electron transfer between OXPHOS complexes or that they play a protective role either by stabilising the individual complexes or by reducing ROS production. However, data in favour and in disfavour of all the different hypotheses exist in the literature and the physiological function of OXPHOS supercomplexes remains an enigma. We have isolated several mutants lacking OXPHOS supercomplexes during the project ‘Control of complex I proteostasis in plants’ and, therefore, a logical follow-up of this project is to use this unique genetic resource to investigate the function of OXPHOS supercomplexes. Under standard growth conditions, none of the supercomplex mutants show altered growth phenotype, we will challenge these mutants with stressful growth conditions to evaluate the physiological important of supercomplexes. Then, we will further characterize these mutants both in terms of mitochondrial structure and organization and in terms of bioenergetics to determine the role(s) of OXPHOS supercomplexes in plant mitochondria.

• DFG Programme: Research Grants