The function of LETM1 (leucine zipper and EF-hand containing transmembrane protein 1, ENSG00000168924) is as follows. Plays an important role in maintenance of mitochondrial morphology and in mediating either calcium or potassium/proton antiport (PubMed:18628306, PubMed:19797662, PubMed:24344246, PubMed:24898248, PubMed:29123128, PubMed:32139798, PubMed:36055214, PubMed:36321428). Mediates proton-dependent calcium efflux from mitochondrion (PubMed:19797662, PubMed:24344246, PubMed:29123128). Also functions as an electroneutral mitochondrial proton/potassium exchanger (PubMed:24898248, PubMed:36055214, PubMed:36321428). Crucial for the maintenance of mitochondrial tubular networks and for the assembly of the supercomplexes of the respiratory chain (PubMed:18628306, PubMed:36055214). Required for the maintenance of the tubular shape and cristae organization (PubMed:18628306, PubMed:32139798). {ECO:0000269|PubMed:18628306, ECO:0000269|PubMed:19797662, ECO:0000269|PubMed:24344246, ECO:0000269|PubMed:24898248, ECO:0000269|PubMed:29123128, ECO:0000269|PubMed:32139798, ECO:0000269|PubMed:36055214, ECO:0000269|PubMed:36321428}.