Functional characterization of the role of evolutionary conserved Rho GTPases at the interface between mitochondria and the endoplasmic reticulum

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Mitochondria form tight connections with a subfraction of the endoplasmic reticulum (ER). These contact sites are required for Ca2+ and phospholipid exchange between both compartments, which is essential for cell viability. The mechanisms mediating and regulating the interaction between both cellular organelles remain poorly understood. Most recently, a protein complex, named ERMES, has been identified to mediate tethering of mitochondria and the ER in yeast. Mutation of the evolutionary conserved rho GTPase Gem1 results in similar phenotypes compared to ERMES mutants as revealed by a systematic genetic analysis. Moreover, Gem1 and ERMES components physically interact with each other, strongly suggesting a role of Gem1 at mito-ER contact sites. In the proposed study, I will characterize the function of Gem1 at these interfaces and will determine the role of the EF hands and GTPase domains of Gem1 in this process. Mammalian cells lack ERMES counterparts, wherefore I will exploit the mammalian Gem1 homologs, Miro1 and Miro2, as starting points for the investigation of mito-ER contact sites in human cells. Finally, I will perform a systematic large scale analysis to comprehensively define the components impacting on the interaction of mitochondria and the ER. Altogether, these analyses hold the promise to significantly enhance our understanding of the formation and regulation of mito-ER contact sites and their importance for diverse cellular processes.