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Journal of Biochemistry Advance Access published online on November 5, 2008
Journal of Biochemistry, doi:10.1093/jb/mvn149
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© The authors 2008. Published by Oxford University Press on behalf of the Japanese Biochemical Society. All rights reserved.

Immunity protein protects colicin E2 from OmpT protease

Denis Duché*, Mohamed Issouf1 and Roland Lloubès

Laboratoire d’Ingénièrie des Systèmes Macromoléculaires, Institut de Biologie Structurale et Microbiologie, CNRS, 31 Chemin Joseph Aiguier, 13402 Marseille cedex 20, France.

*corresponding author: Dr. Denis Duché, Laboratoire d’Ingénièrie des Systèmes Macromoléculaires, Institut de Biologie Structurale et Microbiologie, CNRS, 31 Chemin Joseph Aiguier, 13402 Marseille cedex 20, France. Phone: 33 04 91 16 45 61, Fax: 33 04 91 71 21 24, e-mail: duche{at}ibsm.cnrs-mrs.fr

Received July 4, 2008; Accepted October 21, 2008


  Abstract

The endonuclease colicin E2 (ColE2), a bacteriocidal protein, and the associated cognate immunity protein (Im2) are released from producing Escherichia coli cells. ColE2 interaction with the target cell outer membrane BtuB protein and Tol import machinery allows the dissociation of Im2 from its colicin at the outer membrane surface. Here, we use in vivo approaches to show that a small amount of ColE2-Im2 protein complex bound to sensitive cells is susceptible to proteolytic cleavage by the outer membrane protease, OmpT. The presence of BtuB is required for ColE-Im2 cleavage by OmpT. The amount of colicin cleaved by OmpT is greatly enhanced when ColE2 is dissociated from Im2. We further demonstrate that OmpT cleaves the C-terminal DNase domain of the toxin. As expected, strains that over-produce OmpT are less susceptible to infection by ColE2 than by ColE2-Im2. Our findings reveal an additional function for the immunity protein beside protection of producing cells against their own colicin in the cytoplasm. Im2 protects ColE2 against OmpT-mediated proteolytic attack.

Key Words: BtuB protein, colicin, OmpT protease, translocation, immunity protein

1Present address: Aquapharm Bio-Discovery Ltd. European Centre for Marine Biotechnology


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