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Journal of Bacteriology, June 2007, p. 4217-4222, Vol. 189, No. 11
0021-9193/07/$08.00+0     doi:10.1128/JB.00092-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Colicin E2 Is Still in Contact with Its Receptor and Import Machinery When Its Nuclease Domain Enters the Cytoplasm

Laboratoire d'Ingénièrie des Systèmes Macromoléculaires, Institut de Biologie Structural et Microbiologie, CNRS, 31 Chemin Joseph Aiguier, 13402 Marseille Cedex 20, France

Received 17 January 2007/ Accepted 27 March 2007

Colicins reach their targets in susceptible Escherichia coli strains through two envelope protein systems: the Tol system is used by group A colicins and the TonB system by group B colicins. Colicin E2 (ColE2) is a cytotoxic protein that recognizes the outer membrane receptor BtuB. After gaining access to the cytoplasmic membrane of sensitive Escherichia coli cells, ColE2 enters the cytoplasm to cleave DNA. After binding to BtuB, ColE2 interacts with the Tol system to reach its target. However, it is not known if the entire colicin or only the nuclease domain of ColE2 enters the cell. Here I show that preincubation of ColE2 with Escherichia coli cells prevents binding and translocation of pore-forming colicins of group A but not of group B. This inhibition persisted even when cells were incubated with ColE2 for 30 min before the addition of pore-forming colicins, indicating that ColE2 releases neither its receptor nor its translocation machinery when its nuclease domain enters the cells. These competition experiments enabled me to estimate the time required for ColE2 binding to its receptor and translocation.

Published ahead of print on 6 April 2007.

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