Lipid determinants of Mitofusin-mediated mitochondrial fusion
Project: Lipid determinants of Mitofusin-mediated mitochondrial fusion
Laboratory: Membrane Traffic in Healthy and Diseased Brain
Affiliation: Institute of Psychiatry and Neuroscience of Paris (IPNP); UMR_S1266 INSERM-Paris Descartes University
Address: 102-108, rue de la santé 75014 Paris, France
Name: Thierry Galli
Phone number: 0140789226
Name: David Tareste
Phone number: 0140789249
Subject Keywords: Mitochondria; Membrane fusion; Mitofusin proteins; Lipids; Membrane contact sites
Summary of lab’s interests: Our goal is to elucidate the molecular mechanisms of cellular membrane fusion machineries using a combination of in situ and in vitro approaches. Candidate fusion proteins are either studied within cells or reconstituted into artificial membrane systems with defined and tunable biophysical properties (e.g. supported lipid bilayers, liposomes of various sizes ranging from tens of nanometers to tens of micrometers). The capacity of these proteins to induce membrane docking, deformation and/or fusion is monitored through a combination of spectroscopy and fluorescence or electron microscopy techniques.
Project summary: Mitochondrial fusion is mediated by Mitofusin whose structure consists of an N-terminal GTPase, a first heptad repeat (HR1), a transmembrane region, and a second heptad repeat (HR2). Mutations in any of these domains impair Mitofusin function, but their role in mitochondrial fusion remains controversial. In vitro reconstitution studies by us and others suggest that the HR2 of Mitofusin mediates short distance docking by forming homotypic antiparallel dimers, while the HR1– owing to its amphipathic nature – triggers fusion by perturbing the membrane structure. Mitochondrial fusion is also regulated by specific lipids such as cardiolipin, phosphatidylethanolamine and phosphatidic acid. The exact mode of action of these lipids in mitochondrial fusion is also not fully understood. Mitochondria are found in close association with ER membranes with which they exchange lipids, a process that is believed to occur via membrane contact sites (MCS) and to involve ORP proteins. We hypothesize that ORP-mediated lipid exchange at ER-mitochondria MCS might create a local enrichment of specific lipids in mitochondrial membranes, facilitating Mitofusin-mediated fusion. This PhD project aims at elucidating the mechanisms by which Mitofusin mediates mitochondrial fusion and how this process is regulated by lipids, and functionally coupled to the lipid transport machinery at ER-mitochondria MCS.
Interdisciplinary aspect of the project: The main ambition of this project is to understand the molecular mechanisms of mitochondrial fusion using an integrated approach ranging from molecular biophysics to cell biology. This approach should bridge the gap between in vivo observations and in vitro biophysical assays using recombinant proteins, and thus to allow physiologically relevant conclusions to be drawn from in vitro observations. To this end, we will use a combination of approaches including cell-free in vitro fusion and lipid transport assays, as well as live cell imaging of mitochondrial fusion in situ, and morphological analysis of mitochondria and ER-mitochondria MCS by electron microscopy.
Funding: No. Potential ANR funding (answer in July).