Key regulator of mitochondrial quality that mediates the repairing or degradation of unhealthy mitochondria in response to mitochondrial damage (PubMed:21264221, PubMed:21264228, PubMed:22292033, PubMed:22532927). Mediator of mitochondrial protein catabolic process (also named MALM) by mediating the degradation of damaged proteins inside mitochondria by promoting the accumulation in the mitochondrial matrix of hydrolases that are characteristic of the lysosomal lumen (PubMed:21264221, PubMed:21264228, PubMed:22292033, PubMed:22532927). Also involved in mitochondrion degradation of damaged mitochondria by promoting the formation of vacuole-like structures (named MIV), which engulf and degrade unhealthy mitochondria by accumulating lysosomes (PubMed:21264228). The physical interaction of SPATA18/MIEAP, BNIP3 and BNIP3L/NIX at the mitochondrial outer membrane regulates the opening of a pore in the mitochondrial double membrane in order to mediate the translocation of lysosomal proteins from the cytoplasm to the mitochondrial matrix (PubMed:22292033). Binds cardiolipin (PubMed:38322995). May form molecular condensates (non- membrane-bounded organelles) within mitochondria that compartmentalize and promote cardiolipin metabolism (PubMed:38322995). {ECO:0000269|PubMed:21264221, ECO:0000269|PubMed:21264228, ECO:0000269|PubMed:22292033, ECO:0000269|PubMed:38322995}. This is the function of ENSG00000163071 (SPATA18, spermatogenesis associated 18).