Constitutes the soluble short form (S-MGM1) generated by cleavage by PCP1, which plays a central role in mitochondrial inner membrane fusion and cristae morphology. The transmembrane long form (L-MGM1) and the S-MGM1 form higher-order helical assemblies that coordinate the fusion of mitochondrial inner membranes. Inner membrane-anchored L-MGM1 molecules initiate membrane remodeling by recruiting soluble S-MGM1 to rapidly polymerize into a flexible cylindrical scaffold encaging the mitochondrial inner membrane. Once at the membrane surface, the formation of S-MGM1 helices induce bilayer curvature. MGM1 dimerization through the paddle region, which inserts into cardiolipin-containing membrane, promotes GTP hydrolysis and the helical assembly of a flexible MGM1 lattice on the membrane, which drives membrane curvature and mitochondrial fusion. Excess levels of S-MGM1 produced by cleavage by PCP1 following stress conditions that induce loss of mitochondrial membrane potential, lead to an impaired equilibrium between L-MGM1 and S-MGM1, thereby inhibiting mitochondrial fusion 