Probable transmembrane GTPase, which mediates mitochondrial fusion. Fusion of mitochondria occurs in many cell types and constitutes an important step in mitochondrial morphology, which is balanced between fusion and fission (By similarity). GTP + H2O = GDP + H(+) + phosphate Belongs to the TRAFAC class dynamin-like GTPase superfamily. Dynamin/Fzo/YdjA family. Mitofusin subfamily.