Signals in bacterial beta-barrel proteins are functional in eukaryotic cells for targeting to and assembly in mitochondria.
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.
Walther
Dirk M
DM
Interfaculty Institute for Biochemistry, University of Tübingen, 72076 Tübingen, Germany.
Papic
Drazen
D
Bos
Martine P
MP
Tommassen
Jan
J
Rapaport
Doron
D
D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008856:Microscopy, Fluorescence; D008928:Mitochondria / Q000378:metabolism*; D011487:Protein Conformation; D011956:Receptors, Cell Surface / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics; D015398:Signal Transduction
D001426:Bacterial Proteins; D011956:Receptors, Cell Surface; D011994:Recombinant Proteins