title: The mitochondrial oxidase assembly protein1 (Oxa1) insertase forms a membrane pore in lipid bilayers.
abstract: The inner membrane of mitochondria is especially protein-rich. To direct proteins into the inner membrane, translocases mediate transport and membrane insertion of precursor proteins. Although the majority of mitochondrial proteins are imported from the cytoplasm, core subunits of respiratory chain complexes are inserted into the inner membrane from the matrix. Oxa1, a conserved membrane protein, mediates the insertion of mitochondrion-encoded precursors into the inner mitochondrial membrane. The molecular mechanism by which Oxa1 mediates insertion of membrane spans, entailing the translocation of hydrophilic domains across the inner membrane, is still unknown. We investigated if Oxa1 could act as a protein-conducting channel for precursor transport. Using a biophysical approach, we show that Oxa1 can form a pore capable of accommodating a translocating protein segment. After purification and reconstitution, Oxa1 acts as a cation-selective channel that specifically responds to mitochondrial export signals. The aqueous pore formed by Oxa1 displays highly dynamic characteristics with a restriction zone diameter between 0.6 and 2 nm, which would suffice for polypeptide translocation across the membrane. Single channel analyses revealed four discrete channels per active unit, suggesting that the Oxa1 complex forms several cooperative hydrophilic pores in the inner membrane. Hence, Oxa1 behaves as a pore-forming translocase that is regulated in a membrane potential and substrate-dependent manner.
authors: Biophysik, Universität Osnabrück, FB Biologie/Chemie, D-49034 Osnabrück, Germany.
authors: Vivien
authors: V
authors: Krüger
authors: Markus
authors: M
authors: Deckers
authors: Markus
authors: M
authors: Hildenbeutel
authors: Martin
authors: M
authors: van der Laan
authors: Maike
authors: M
authors: Hellmers
authors: Christina
authors: C
authors: Dreker
authors: Marc
authors: M
authors: Preuss
authors: Johannes M
authors: JM
authors: Herrmann
authors: Peter
authors: P
authors: Rehling
authors: Richard
authors: R
authors: Wagner
authors: Michael
authors: M
authors: Meinecke
mesh_terms: D001703:Biophysics / Q000379:methods; D002412:Cations; D002942:Circular Dichroism; D003576:Electron Transport Complex IV / Q000378:metabolism*; D004594:Electrophysiology / Q000379:methods; D008051:Lipid Bilayers / Q000737:chemistry*; D008081:Liposomes / Q000737:chemistry; D008564:Membrane Potentials; D008928:Mitochondria / Q000378:metabolism; D051336:Mitochondrial Membranes / Q000378:metabolism; D024101:Mitochondrial Proteins / Q000378:metabolism*; D009687:Nuclear Proteins / Q000378:metabolism*; D010455:Peptides / Q000737:chemistry; D017433:Protein Structure, Secondary; D021381:Protein Transport; D011994:Recombinant Proteins / Q000737:chemistry; D012441:Saccharomyces cerevisiae / Q000378:metabolism
chemical_list: D002412:Cations; D008051:Lipid Bilayers; D008081:Liposomes; D024101:Mitochondrial Proteins; D009687:Nuclear Proteins; C090858:OXA1 protein; D010455:Peptides; D011994:Recombinant Proteins; D003576:Electron Transport Complex IV