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Proc Natl Acad Sci U S A. 2009 Feb 24;106(8):2531-6. doi: 10.1073/pnas.0807830106. Epub 2009 Jan 30.

Signals in bacterial beta-barrel proteins are functional in eukaryotic cells for targeting to and assembly in mitochondria.

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  • 1Interfaculty Institute for Biochemistry, University of Tübingen, 72076 Tübingen, Germany.

Abstract

The outer membranes of Gram-negative bacteria, mitochondria, and chloroplasts harbor beta-barrel proteins. The signals that allow precursors of such proteins to be targeted to mitochondria were not characterized so far. To better understand the mechanism by which beta-barrel precursor proteins are recognized and sorted within eukaryotic cells, we expressed the bacterial beta-barrel proteins PhoE, OmpA, Omp85, and OmpC in Saccharomyces cerevisiae and demonstrated that they were imported into mitochondria. A detailed investigation of the import pathway of PhoE revealed that it is shared with mitochondrial beta-barrel proteins. PhoE interacts initially with surface import receptors, and its further sorting depends on components of the TOB/SAM complex. The bacterial Omp85 and PhoE integrated into the mitochondrial outer membrane as native-like oligomers. For the latter protein this assembly depended on the C-terminal Phe residue, which is important also for the correct assembly of PhoE into the bacterial outer membrane. Collectively, it appears that mitochondrial beta-barrel proteins have not evolved eukaryotic-specific signals to ensure their import into mitochondria. Furthermore, the signal for assembly of beta-barrel proteins into the bacterial outer membrane is functional in mitochondria.

PMID:
19181862
[PubMed - indexed for MEDLINE]
PMCID:
PMC2650298
Free PMC Article
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