title: GxxxG motifs hold the TIM23 complex together.
abstract: Approximately 99% of the mitochondrial proteome is nucleus-encoded, synthesized in the cytosol, and subsequently imported into and sorted to the correct compartment in the organelle. The translocase of the inner mitochondrial membrane 23 (TIM23) complex is the major protein translocase of the inner membrane, and is responsible for translocation of proteins across the inner membrane and their insertion into the inner membrane. Tim23 is the central component of the complex that forms the import channel. A high-resolution structure of the import channel is still missing, and structural elements important for its function are unknown. In the present study, we analyzed the importance of the highly abundant GxxxG motifs in the transmembrane segments of Tim23 for the structural integrity of the TIM23 complex. Of 10 glycines present in the GxxxG motifs in the first, second and third transmembrane segments of Tim23, mutations of three of them in transmembrane segments 1 and 2 resulted in a lethal phenotype, and mutations of three others in a temperature-sensitive phenotype. The remaining four caused no obvious growth phenotype. Importantly, none of the mutations impaired the import and membrane integration of Tim23 precursor into mitochondria. However, the severity of growth impairment correlated with the destabilization of the TIM23 complex. We conclude that the GxxxG motifs found in the first and second transmembrane segments of Tim23 are necessary for the structural integrity of the TIM23 complex.
authors.affiliation: Department of Biochemistry and Molecular Biology, The George S. Wise Faculty of Life Sciences, Tel Aviv University, Israel.
authors.forename: Keren
authors.initials: K
authors.lastname: Demishtein-Zohary
authors.affiliation: Department of Biochemistry and Molecular Biology, The George S. Wise Faculty of Life Sciences, Tel Aviv University, Israel.
authors.forename: Milit
authors.initials: M
authors.lastname: Marom
authors.affiliation: Max Planck Institute of Biochemistry, Munich, Germany.
authors.forename: Walter
authors.initials: W
authors.lastname: Neupert
authors.affiliation: Institute for Physiological Chemistry, University of Munich, Munich, Germany.
authors.forename: Dejana
authors.initials: D
authors.lastname: Mokranjac
authors.affiliation: Department of Biochemistry and Molecular Biology, The George S. Wise Faculty of Life Sciences, Tel Aviv University, Israel.
authors.forename: Abdussalam
authors.initials: A
authors.lastname: Azem
mesh_terms: D020816:Amino Acid Motifs; D026901:Membrane Transport Proteins / Q000737:chemistry / Q000502:physiology*; D008928:Mitochondria / Q000378:metabolism; D000090622:Mitochondrial Precursor Protein Import Complex Proteins; D008969:Molecular Sequence Data; D046912:Multiprotein Complexes / Q000378:metabolism; D011485:Protein Binding; D055550:Protein Stability; D017433:Protein Structure, Secondary; D021381:Protein Transport; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000254:growth & development; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000502:physiology*
chemical_list: D026901:Membrane Transport Proteins; D000090622:Mitochondrial Precursor Protein Import Complex Proteins; D046912:Multiprotein Complexes; D029701:Saccharomyces cerevisiae Proteins; C083081:TIM23 protein, S cerevisiae
keywords: Tim17; Tim23; Tim44; import channel; mitochondrial protein import