期刊
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
卷 108, 期 33, 页码 13841-13846出版社
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1108626108
关键词
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资金
- Deutsche Forschungsgemeinschaft [SFB-807]
- Cluster of Excellence Macromolecular Complexes
- Graduate School [1216]
- Center of Membrane Proteomics Frankfurt
- Max Planck Foundation
The majority of outer membrane proteins (OMPs) from Gram-negative bacteria and many of mitochondria and chloroplasts are beta-barrels. Insertion and assembly of these proteins are catalyzed by the Omp85 protein family in a seemingly conserved process. All members of this family exhibit a characteristic N-terminal polypeptide-transport-associated (POTRA) and a C-terminal 16-stranded beta-barrel domain. In plants, two phylogenetically distinct and essential Omp85's exist in the chloroplast outer membrane, namely Toc75-III and Toc75-V. Whereas Toc75-V, similar to the mitochondrial Sam50, is thought to possess the original bacterial function, its homolog, Toc75-III, evolved to the pore-forming unit of the TOC translocon for preprotein import. In all current models of OMP biogenesis and preprotein translocation, a topology of Omp85 with the POTRA domain in the periplasm or intermembrane space is assumed. Using self-assembly GFP-based in vivo experiments and in situ topology studies by electron cryotomography, we show that the POTRA domains of both Toc75-III and Toc75-V are exposed to the cytoplasm. This unexpected finding explains many experimental observations and requires a reevaluation of current models of OMP biogenesis and TOC complex function.
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