Dynamin-related GTPase that is essential for normal mitochondrial morphology by regulating the equilibrium between mitochondrial fusion and mitochondrial fission. Binds lipid membranes enriched in negatively charged phospholipids, such as cardiolipin, and promotes membrane tubulation. The intrinsic GTPase activity is low, and is strongly increased by interaction with lipid membranes (By similarity). Plays a role in remodeling cristae and the release of cytochrome c during apoptosis (By similarity). Proteolytic processing in response to intrinsic apoptotic signals may lead to disassembly of OPA1 oligomers and release of the caspase activator cytochrome C (CYCS) into the mitochondrial intermembrane space (By similarity). Plays a role in mitochondrial genome maintenance (By similarity). Inactive form produced by cleavage at S1 position by OMA1 following stress conditions that induce loss of mitochondrial membrane potential, leading to negative regulation of mitochondrial fusion. Dynamin-like 120 kDa protein, form S2: Produced by cleavage at position S2 by YME1L. Promotes mitochondrial fusion. GTP + H2O = GDP + H(+) + phosphate Activated by guanine nucleotide exchange factor RCC1L. Oligomeric complex consisting of membrane-bound and soluble forms of OPA1. Interacts with CHCHD3 and IMMT; these interactions occur preferentially with soluble OPA1 forms. Interacts with RCC1L; this interaction is direct (By similarity). Binds PARL (By similarity). Interacts with PRELID1 (By similarity). Detected at contact sites between endoplasmic reticulum and mitochondrion membranes. PARL-dependent proteolytic processing releases an antiapoptotic soluble form not required for mitochondrial fusion. Cleaved by OMA1 at position S1 following stress conditions. Belongs to the TRAFAC class dynamin-like GTPase superfamily. Dynamin/Fzo/YdjA family.