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Journal of Bacteriology, December 1998, p. 6433-6439, Vol. 180, No. 24
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

Mutational Analysis of the Escherichia coli K-12 TolA N-Terminal Region and Characterization of Its TolQ-Interacting Domain by Genetic Suppression

Pierre Germon, Thierry Clavel, Anne Vianney, Raymond Portalier, and Jean Claude Lazzaroni*

Laboratoire de Microbiologie et Génétique Moléculaire, CNRS-Université Lyon I, F-69622 Villeurbanne Cedex, France

Received 15 July 1998/Accepted 26 September 1998

The Tol-Pal proteins of Escherichia coli are involved in maintaining outer membrane integrity. They form two complexes in the cell envelope. Transmembrane domains of TolQ, TolR, and TolA interact in the cytoplasmic membrane, while TolB and Pal form a complex near the outer membrane. The N-terminal transmembrane domain of TolA anchors the protein to the cytoplasmic membrane and interacts with TolQ and TolR. Extensive mutagenesis of the N-terminal part of TolA was carried out to characterize the residues involved in such processes. Mutations affecting the function of TolA resulted in a lack or an alteration in TolA-TolQ or TolR-TolA interactions but did not affect the formation of TolQ-TolR complexes. Our results confirmed the importance of residues serine 18 and histidine 22, which are part of an SHLS motif highly conserved in the TolA and the related TonB proteins from different organisms. Genetic suppression experiments were performed to restore the functional activity of some tolA mutants. The suppressor mutations all affected the first transmembrane helix of TolQ. These results confirmed the essential role of the transmembrane domain of TolA in triggering interactions with TolQ and TolR.

* Corresponding author. Mailing address: Laboratoire de Microbiologie et Génétique Moléculaire, CNRS-Université Lyon I, bât. 405, F-69622 Villeurbanne Cedex, France. Phone: (33) 472 43 13 67. Fax: (33) 472 43 19 71. E-mail: lazzaroni{at}biomserv.univ-lyon1.fr.

Journal of Bacteriology, December 1998, p. 6433-6439, Vol. 180, No. 24
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.


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