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Article
Nature Structural Biology  9, 476 - 484 (2002)
Published online: 20 May 2002; | doi:10.1038/nsb797

The cytotoxic domain of colicin E9 is a channel-forming endonuclease

Khédidja Mosbahi1, 2, Christelle Lemaître1, 2, 3, Anthony H. Keeble1, Hamid Mobasheri1, 4, Bertrand Morel5, Richard James6, Geoffrey R. Moore5, Edward J.A. Lea1 & Colin Kleanthous1

1  School of Biological Sciences, University of East Anglia, Norwich, NR4 7TJ, UK.

2  These authors contributed equally to this work.

3  Present address: Laboratoire de Spectrométrie de Masse Bioorganique, Université Louis Pasteur, UMR/ULP CNRS 7509, ECPM 25 rue Becquerel, F-67087 Cedex 2, France.

4  Present address: Laboratory of Membrane Biophysics, Institute of Biochemistry and Biophysics, University of Tehran, PO Box 13145-1384, IR Iran.

5  School of Chemical Sciences, University of East Anglia, Norwich, NR4 7TJ, UK.

6  Division of Microbiology and Infectious Diseases, University Hospital, Queen's Medical Centre, University of Nottingham, Nottingham NG7 2UH, UK.

Correspondence should be addressed to Colin Kleanthous c.kleanthous@uea.ac.uk
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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Nature Structural & Molecular Biology
ISSN: 1545-9993
EISSN: 1545-9985
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