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
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• PubMed

Reference Type

Journal Article | Research Support, Non-U.S. Gov't

Authors

Walther DM, Papic D, Bos MP, Tommassen J, Rapaport D

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