Abstract
Bacterial toxins commonly translocate cytotoxic enzymes into cells using channel-forming subunits or domains as conduits. Here we demonstrate that the small cytotoxic endonuclease domain from the bacterial toxin colicin E9 (E9 DNase) shows nonvoltage-gated, channel-forming activity in planar lipid bilayers that is linked to toxin translocation into cells. A disulfide bond engineered into the DNase abolished channel activity and colicin toxicity but left endonuclease activity unaffected; NMR experiments suggest decreased conformational flexibility as the likely reason for these alterations. Concomitant with the reduction of the disulfide bond is the restoration of conformational flexibility, DNase channel activity and colicin toxicity. Our data suggest that endonuclease domains of colicins may mediate their own translocation across the bacterial inner membrane through an intrinsic channel activity that is dependent on structural plasticity in the protein.
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Acknowledgements
We thank A. Reilly, C. Moore and N. Cull for expert technical assistance and A. Leech for help with the acquisition of all mass spectrometry data. We also thank the referees of this paper for their helpful comments. This work was supported by The Biotechnology and Biological Sciences Research Council. A.H.K. was supported by a Wellcome Trust Prize Studentship.
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Mosbahi, K., Lemaître, C., Keeble, A. et al. The cytotoxic domain of colicin E9 is a channel-forming endonuclease. Nat Struct Mol Biol 9, 476–484 (2002). https://doi.org/10.1038/nsb797
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DOI: https://doi.org/10.1038/nsb797
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