title: The cytotoxic domain of colicin E9 is a channel-forming endonuclease.
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.
authors.affiliation: School of Biological Sciences, University of East Anglia, Norwich, NR4 7TJ, UK.
authors.forename: Khédidja
authors.initials: K
authors.lastname: Mosbahi
authors.forename: Christelle
authors.initials: C
authors.lastname: Lemaître
authors.forename: Anthony H
authors.initials: AH
authors.lastname: Keeble
authors.forename: Hamid
authors.initials: H
authors.lastname: Mobasheri
authors.forename: Bertrand
authors.initials: B
authors.lastname: Morel
authors.forename: Richard
authors.initials: R
authors.lastname: James
authors.forename: Geoffrey R
authors.initials: GR
authors.lastname: Moore
authors.forename: Edward J A
authors.initials: EJ
authors.lastname: Lea
authors.forename: Colin
authors.initials: C
authors.lastname: Kleanthous
mesh_terms: D001665:Binding Sites; D001692:Biological Transport; D002463:Cell Membrane Permeability; D003087:Colicins / Q000737:chemistry* / Q000378:metabolism*; D003851:Deoxyribonucleases / Q000737:chemistry* / Q000378:metabolism*; D004220:Disulfides / Q000378:metabolism; D004553:Electric Conductivity; D008051:Lipid Bilayers / Q000737:chemistry / Q000378:metabolism; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D010084:Oxidation-Reduction; D018408:Patch-Clamp Techniques; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D013329:Structure-Activity Relationship
chemical_list: D003087:Colicins; D004220:Disulfides; D008051:Lipid Bilayers; D003851:Deoxyribonucleases