Structural mechanism of mitochondrial membrane remodelling by human OPA1

Distinct morphologies of the mitochondrial network support divergent metabolic and regulatory processes that determine cell function and fate 1 – 3 . The mechanochemical GTPase optic atrophy 1 (OPA1) influences the architecture of cristae and catalyses the fusion of the mitochondrial inner membrane 4 , 5 . Despite its fundamental importance, the molecular mechanisms by which OPA1 modulates mitochondrial morphology are unclear. Here, using a combination of cellular and structural analyses, we illuminate the molecular mechanisms that are key to OPA1-dependent membrane remodelling and fusion. Human OPA1 embeds itself into cardiolipin-containing membranes through a lipid-binding paddle domain. A conserved loop within the paddle domain inserts deeply into the bilayer, further stabilizing the interactions with cardiolipin-enriched membranes. OPA1 dimerization through the paddle domain promotes the helical assembly of a flexible OPA1 lattice on the membrane, which drives mitochondrial fusion in cells. Moreover, the membrane-bending OPA1 oligomer undergoes conformational changes that pull the membrane-inserting loop out of the outer leaflet and contribute to the mechanics of membrane remodelling. Our findings provide a structural framework for understanding how human OPA1 shapes mitochondrial morphology and show us how human disease mutations compromise OPA1 functions. Human OPA1 embeds itself into cardiolipin-containing membranes through a lipid-binding paddle domain, and OPA1 oligomerization through multiple assembly interfaces promotes the helical assembly of a flexible OPA1 lattice on the membrane, driving mitochondrial fusion in cells.