Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 102, Issue 1, Pages 221-226Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.0406055102
Keywords
Escherichia coli; microbial pathogenesis; protein folding; protein translocation
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Bacterial autotransporters are proteins that use a C-terminal porin-like domain to facilitate the transport of an upstream passenger domain across the outer membrane. Although autotransporters are translocated across the inner membrane (IM) via the Sec pathway, some of them contain exceptionally long signal peptides distinguished by a unique N-terminal sequence motif. In this study, we used the Escherichia coli O157:H7 autotransporter EspP as a model protein to investigate the function of the unusual signal peptides. We found that removal of the N-terminal motif or replacement of the EspP signal peptide did not affect translocation of the protein across the IM. Remarkably, modification of the signal peptide caused EspP to misfold in the periplasm and blocked transport of the passenger domain across the outer membrane. Further analysis suggested that the EspP signal peptide transits slowly through the Sec machinery. Based on these results, we propose that the unusual signal peptides not only function as targeting signals, but also prevent misfolding of the passenger domain in the periplasm by transiently tethering it to the IM.
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