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Chloroplast Omp85 proteins change orientation during evolution

MPG-Autoren
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Daum,  Bertram
Department of Structural Biology, Max Planck Institute of Biophysics, Max Planck Society;

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Kühlbrandt,  Werner
Department of Structural Biology, Max Planck Institute of Biophysics, Max Planck Society;

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Zitation

Sommer, M. S., Daum, B., Gross, L. E., Weis, B. L. M., Mirus, O., Abram, L., et al. (2011). Chloroplast Omp85 proteins change orientation during evolution. Proceedings of the National Academy of Sciences of the United States of America, 108(33), 13841-13846.


Zitierlink: http://hdl.handle.net/11858/00-001M-0000-0024-D63B-D
Zusammenfassung
The majority of outer membrane proteins (OMPs) from Gram- negative bacteria and many of mitochondria and chloroplasts are β-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 polypep- tide-transport–associated (POTRA) and a C-terminal 16-stranded β-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 do- main 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 un- expected finding explains many experimental observations and requires a reevaluation of current models of OMP biogenesis and TOC complex function.