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Journal of Bacteriology, January 2008, p. 21-27, Vol. 190, No. 1
0021-9193/08/$08.00+0     doi:10.1128/JB.01389-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

HasB, the Serratia marcescens TonB Paralog, Is Specific to HasR{triangledown}

Najla Benevides-Matos, Cécile Wandersman, and Francis Biville*

Unité des Membranes Bactériennes Institut Pasteur (CNRS URA 2172), 25 Rue du Dr. Roux, Paris Cedex 15, France

Received 27 August 2007/ Accepted 10 October 2007

Serratia marcescens possesses two functional TonB paralogs, TonBSm and HasB, for energizing TonB-dependent transport receptors (TBDT). Previous work had shown that HasB is specific to heme uptake in the natural host and in Escherichia coli expressing the S. marcescens TBDT receptor HasR, whereas the S. marcescens TonB and E. coli TonB proteins function equally well with various TBDT receptors for heme and siderophores. This has raised the question of the target of this specificity. HasB could be specific either to heme TBDT receptors or only to HasR. To resolve this question, we have cloned in E. coli another S. marcescens heme receptor, HemR, and we show here that this receptor is TonB dependent and does not work with HasB. This demonstrates that HasB is not dedicated to heme TBDT receptors but rather forms a specific pair with HasR. This is the first reported case of a specific TonB protein working with only one TBDT receptor in one given species. We discuss the occurrence, possible molecular mechanisms, and selective advantages of such dedicated TonB paralogs.

* Corresponding author. Mailing address: Unité des Membranes Bactériennes Institut Pasteur (CNRS URA 2172), 25 Rue du Dr. Roux, Paris Cedex 15, France. Phone: 33-1-40-61-32-77. Fax: 33-1-45-68-89-38. E-mail: fbiville{at}pasteur.fr

{triangledown} Published ahead of print on 19 October 2007.

Journal of Bacteriology, January 2008, p. 21-27, Vol. 190, No. 1
0021-9193/08/$08.00+0     doi:10.1128/JB.01389-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.





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