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Journal of Bacteriology, November 2005, p. 7526-7534, Vol. 187, No. 21
0021-9193/05/$08.00+0     doi:10.1128/JB.187.21.7526-7534.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Tol-Dependent Macromolecule Import through the Escherichia coli Cell Envelope Requires the Presence of an Exposed TolA Binding Motif

Stéphanie Pommier, Marthe Gavioli, Eric Cascales, and Roland Lloubès^*

Institut de Biologie Structurale et de Microbiologie, CNRS, UPR 9027, 31 Chemin Joseph Aiguier, 13402 Marseille Cedex 20, France

Received 20 May 2005/ Accepted 18 August 2005

The Tol-Pal proteins of the cell envelope of Escherichia coli are required for maintaining outer membrane integrity. This system forms protein complexes in which TolA plays a central role by providing a bridge between the inner and outer membranes via its interaction with the Pal lipoprotein. The Tol proteins are parasitized by filamentous bacteriophages and group A colicins. The N-terminal domain of the Ff phage g3p protein and the translocation domains of colicins interact directly with TolA during the processes of import through the cell envelope. Recently, a four-amino-acid sequence in Pal has been shown to be involved in Pal's interaction with TolA. A similar motif is also present in the sequence of two TolA partners, g3p and colicin A. Here, a mutational study was conducted to define the function of these motifs in the binding activity and import process of TolA. The various domains were produced and exported to the bacterial periplasm, and their cellular effects were analyzed. Cells producing the g3p domain were tolerant to colicins and filamentous phages and had destabilized outer membranes, while g3p deleted of three residues in the motif was affected in TolA binding and had no effect on cell integrity or colicin or phage import. A conserved Tyr residue in the colicin A translocation domain was involved in TolA binding and colicin A import. Furthermore, in vivo and in vitro coprecipitation analyses demonstrated that colicin A and g3p N-terminal domains compete for binding to TolA.

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* Corresponding author. Mailing address: Institut de Biologie Structurale et de Microbiologie, CNRS, UPR 9027, 31 Chemin Joseph Aiguier, 13402 Marseille Cedex 20, France. Phone: (33) 4 91 16 46 63. Fax: (33) 4 91 71 21 24. E-mail: lloubes{at}ibsm.cnrs-mrs.fr.

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Journal of Bacteriology, November 2005, p. 7526-7534, Vol. 187, No. 21
0021-9193/05/$08.00+0     doi:10.1128/JB.187.21.7526-7534.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

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