title: HasB, the Serratia marcescens TonB paralog, is specific to HasR.
abstract: Serratia marcescens possesses two functional TonB paralogs, TonB(Sm) 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.
authors.affiliation: Unité des Membranes Bactériennes Institut Pasteur (CNRS URA 2172), 25 Rue du Dr. Roux, Paris Cedex 15, France.
authors.forename: Najla
authors.initials: N
authors.lastname: Benevides-Matos
authors.forename: Cécile
authors.initials: C
authors.lastname: Wandersman
authors.forename: Francis
authors.initials: F
authors.lastname: Biville
mesh_terms: D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics / Q000502:physiology*; D002352:Carrier Proteins / Q000502:physiology; D002417:Cattle; D002876:Chromosomes, Bacterial; D003001:Cloning, Molecular; D017931:DNA Primers; D004269:DNA, Bacterial / Q000235:genetics / Q000302:isolation & purification; D017353:Gene Deletion; D006418:Heme / Q000493:pharmacokinetics / Q000494:pharmacology; D006427:Hemin / Q000494:pharmacology; D006454:Hemoglobins / Q000494:pharmacology; D008565:Membrane Proteins / Q000235:genetics / Q000502:physiology*; D010957:Plasmids; D012706:Serratia marcescens / Q000145:classification / Q000187:drug effects / Q000235:genetics* / Q000254:growth & development
chemical_list: D001426:Bacterial Proteins; D002352:Carrier Proteins; D017931:DNA Primers; D004269:DNA, Bacterial; C093956:HasA protein, Serratia marcescens; C447836:HasB protein, Serratia marcescens; D006454:Hemoglobins; D008565:Membrane Proteins; D006418:Heme; D006427:Hemin