Key regulator of mitochondrial quality that mediates the repairing or degradation of unhealthy mitochondria in response to mitochondrial damage. 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. 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 (By similarity). 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 (By similarity). Interacts (via coiled-coil domains) with BNIP3L (via BH3 domain). Interacts (via coiled-coil domains) with BNIP3 (via BH3 domain). Colocalizes with BNIP3 and BNIP3L at the mitochondrion outer membrane. Localizes to the cytoplasm under normal conditions. Relocalizes to mitochondrion outer membrane following cellular stress. Belongs to the MIEAP family.