How NINJ1 mediates plasma membrane rupture and why NINJ2 cannot
NINJ1 is a recently identified active executioner of plasma membrane rupture (PMR), a process previously thought to be a passive osmotic lysis event in lytic cell death. NINJ2 is a close paralog of NINJ1 but it failed to mediate PMR. By cryoEM, we found that both NINJ1 and NINJ2 were able to assemble into linear filament that binds strongly to lipids on one side but is water-soluble on the other side. The more-or-less straight NINJ1 filament was able to wrap around a membrane bleb and solubilize it from the plasma membrane to induce PMR; however, the intrinsically curved NINJ2 filament failed to do so, explaining its incapability of mediating PMR. We further demonstrated that binding to cholesterol at the inner leaflet of the lipid bilayer was responsible for the curving of the NINJ2 filament, while strong lipid binding at the outer leaflet was contributing to NINJ1s capability of mediating PMR.