The invention of the present application provides an isolated and purified human mitochondrial protein comprising the amino acid sequence of SEQ ID NO: 2 or SEQ ID NO: 4, which is a novel human protein promoting aggregation and fusion of mitochondria. The present invention also provides a polynucleotide encoding such a mitochondrial protein, antibody against such a mitochondrial protein, and a proteoliposome composed of such a mitochondrial protein and lipid. Mitochondrial proteins are useful for clarifying causes of mitochondrial diseases as well as for developing preventive and therapeutic methods thereof. Furthermore, antibodies and probes derived from genes encoding such proteins are potentially useful materials for diagnosis of condition of mitochondria in particular diseases. Furthermore, proteoliposomes provide measures for specific transfer of foreign genes or drugs targeted toward mitochondria.