Identification of new channels by systematic analysis of the mitochondrial outer membrane
Krüger V, Becker T, Becker L, Montilla-Martinez M, Ellenrieder L, Vögtle FN, Meyer HE, Ryan MT, Wiedemann N, Warscheid B, Pfanner N, Wagner R, Meisinger C.
Mitochondria have to exchange various molecules with the cell environment including proteins and metabolites. The outer membrane is equipped with channel-forming beta-barrel proteins. Tom40, Sam50 and Mdm10 form protein-conducting channels. The voltage-dependent anion channel (VDAC) allows the flux of metabolites. We report the presence of four additional channel activities in purified outer membrane vesicles from yeast mitochondria. We found two novel anion-selective channel activities. In addition, we characterized two cation-selective channels on molecular level. First, the short-chain dehydrogenase Ayr1 forms a NADPH-regulated channel. Second, the central component of the mitochondrial import machinery (MIM complex) Mim1 forms a channel with predicted alpha-helical structure for protein import. We conclude that the number of channels in the mitochondrial outer membrane is considerably larger than previously thought. The existence of several channels point to specific transport events at the mitochondrial outer membrane.