title: Chloroplast β-barrel proteins are assembled into the mitochondrial outer membrane in a process that depends on the TOM and TOB complexes.
abstract: Membrane-embedded β-barrel proteins are found in the outer membranes (OM) of Gram-negative bacteria, mitochondria and chloroplasts. In eukaryotic cells, precursors of these proteins are synthesized in the cytosol and have to be sorted to their corresponding organelle. Currently, the signal that ensures their specific targeting to either mitochondria or chloroplasts is ill-defined. To address this issue, we studied targeting of the chloroplast β-barrel proteins Oep37 and Oep24. We found that both proteins can be integrated in vitro into isolated plant mitochondria. Furthermore, upon their expression in yeast cells Oep37 and Oep24 were exclusively located in the mitochondrial OM. Oep37 partially complemented the growth phenotype of yeast cells lacking Porin, the general metabolite transporter of this membrane. Similarly to mitochondrial β-barrel proteins, Oep37 and Oep24 expressed in yeast cells were assembled into the mitochondrial OM in a pathway dependent on the TOM and TOB complexes. Taken together, this study demonstrates that the central mitochondrial components that mediate the import of yeast β-barrel proteins can deal with precursors of chloroplast β-barrel proteins. This implies that the mitochondrial import machinery does not recognize signals that are unique to mitochondrial β-barrel proteins. Our results further suggest that dedicated targeting factors had to evolve in plant cells to prevent mis-sorting of chloroplast β-barrel proteins to mitochondria.
authors: Interfaculty Institute of Biochemistry, University of Tübingen, 72076 Tübingen,Germany.
authors: Thomas
authors: T
authors: Ulrich
authors: Lucia E
authors: LE
authors: Gross
authors: Maik S
authors: MS
authors: Sommer
authors: Enrico
authors: E
authors: Schleiff
authors: Doron
authors: D
authors: Rapaport
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism*; D001692:Biological Transport / Q000502:physiology; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D060365:Chloroplast Proteins / Q000235:genetics / Q000378:metabolism*; D015870:Gene Expression; D005816:Genetic Complementation Test; D007473:Ion Channels; D008928:Mitochondria / Q000235:genetics / Q000378:metabolism*; D000090622:Mitochondrial Precursor Protein Import Complex Proteins; D018532:Pisum sativum / Q000235:genetics / Q000378:metabolism*; D010940:Plant Proteins; D021382:Protein Sorting Signals / Q000502:physiology*; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D002352:Carrier Proteins; D060365:Chloroplast Proteins; D007473:Ion Channels; D000090622:Mitochondrial Precursor Protein Import Complex Proteins; C113819:OEP24 protein, Pisum sativum; D010940:Plant Proteins; D021382:Protein Sorting Signals; D029701:Saccharomyces cerevisiae Proteins