Role of the ABC transporter Mdl1 in peptide export from mitochondria

ATP-binding cassette (ABC) adenosine triphosphatases actively transport a w ide variety of compounds across biological membranes. Here, the ABC protein Mdl1 was identified as an intracellular peptide transporter localized in t he inner membrane of yeast mitochondria. Mdl1 was required for mitochondria l export of peptides with molecular masses of similar to 2100 to 600 dalton s generated by proteolysis of inner-membrane proteins by the m-AAA protease in the mitochondrial matrix. Proteolysis by the I-AAA protease in the inte rmembrane space led to the release of similar-sited peptides independent of Mdl1. Thus, two pathways of peptide efflux from mitochondria exist that ma y allow communication between mitochondria and their cellular environment.