title: Mitochondria use different mechanisms for transport of multispanning membrane proteins through the intermembrane space.
abstract: The mitochondrial inner membrane contains numerous multispanning integral proteins. The precursors of these hydrophobic proteins are synthesized in the cytosol and therefore have to cross the mitochondrial outer membrane and intermembrane space to reach the inner membrane. While the import pathways of noncleavable multispanning proteins, such as the metabolite carriers, have been characterized in detail by the generation of translocation intermediates, little is known about the mechanism by which cleavable preproteins of multispanning proteins, such as Oxa1, are transferred from the outer membrane to the inner membrane. We have identified a translocation intermediate of the Oxa1 preprotein in the translocase of the outer membrane (TOM) and found that there are differences from the import mechanisms of carrier proteins. The intermembrane space domain of the receptor Tom22 supports the stabilization of the Oxa1 intermediate. Transfer of the Oxa1 preprotein to the inner membrane is not affected by inactivation of the soluble TIM complexes. Both the inner membrane potential and matrix heat shock protein 70 are essential to release the preprotein from the TOM complex, suggesting a close functional cooperation of the TOM complex and the presequence translocase of the inner membrane. We conclude that mitochondria employ different mechanisms for translocation of multispanning proteins across the aqueous intermembrane space.
authors.affiliation: Institut für Biochemie und Molekularbiologie. Fakultät für Biologie, Universität Freiburg, D-79104 Freiburg, Germany.
authors.forename: Ann E
authors.initials: AE
authors.lastname: Frazier
authors.forename: Agnieszka
authors.initials: A
authors.lastname: Chacinska
authors.forename: Kaye N
authors.initials: KN
authors.lastname: Truscott
authors.forename: Bernard
authors.initials: B
authors.lastname: Guiard
authors.forename: Nikolaus
authors.initials: N
authors.lastname: Pfanner
authors.forename: Peter
authors.initials: P
authors.lastname: Rehling
mesh_terms: D003576:Electron Transport Complex IV; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism; D046911:Macromolecular Substances; D008564:Membrane Potentials; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D026901:Membrane Transport Proteins; D008928:Mitochondria / Q000378:metabolism*; D033681:Mitochondrial Membrane Transport Proteins; D024101:Mitochondrial Proteins / Q000235:genetics / Q000378:metabolism*; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D011498:Protein Precursors / Q000235:genetics / Q000378:metabolism; D021381:Protein Transport; D011956:Receptors, Cell Surface; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: C409465:COX18 protein, S cerevisiae; D005656:Fungal Proteins; D018840:HSP70 Heat-Shock Proteins; D046911:Macromolecular Substances; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D033681:Mitochondrial Membrane Transport Proteins; D024101:Mitochondrial Proteins; D009687:Nuclear Proteins; C090858:OXA1 protein; D011498:Protein Precursors; D011956:Receptors, Cell Surface; D029701:Saccharomyces cerevisiae Proteins; C090857:TOM22 protein, S cerevisiae; D003576:Electron Transport Complex IV