title: Haemophore-mediated signal transduction across the bacterial cell envelope in Serratia marcescens: the inducer and the transported substrate are different molecules.
abstract: Numerous bacteria are able to use free and haemoprotein-bound haem as iron sources because of the action of small secreted proteins called haemophores. Haemophores have very high affinity for haem, and can therefore extract haem from the haem-carrier proteins and deliver it to the cells by means of specific cell surface receptors. Haem is then taken up and the empty haemophores are recycled. Here, we report a study of the regulation of the Serratia marcescens has operon which is involved in haemophore-dependent haem acquisition. We characterized two genes encoding proteins homologous to specific ECF sigma and antisigma factors. We showed that they regulate the synthesis of the haemophore-specific outer membrane receptor, HasR, by a signal transduction mechanism similar to the siderophore surface-signalling systems. We also showed the essential role of HasR itself in this process. Using haem-loaded and haem-free haemophore, we identified the stimulus for the HasR-mediated signal transduction as being the binding of the haem-loaded haemophore to HasR. Thus, unlike siderophore-uptake systems, in which the signalling molecule is the transported substrate itself, in the haemophore-dependent haem uptake system the inducer and the transported substrate are different compounds.
authors.affiliation: Groupe de Génétique des Biofilms Institut Pasteur (CNRS URA 2172), 25 rue du Dr Roux, Paris CEDEX 15, France.
authors.forename: Maria-Silvia
authors.initials: MS
authors.lastname: Rossi
authors.forename: Annick
authors.initials: A
authors.lastname: Paquelin
authors.forename: Jean Marc
authors.initials: JM
authors.lastname: Ghigo
authors.forename: Cécile
authors.initials: C
authors.lastname: Wandersman
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D001692:Biological Transport; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D006418:Heme / Q000378:metabolism*; D006454:Hemoglobins / Q000378:metabolism; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D009876:Operon; D012706:Serratia marcescens / Q000235:genetics / Q000378:metabolism*; D012808:Sigma Factor / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction
chemical_list: D001426:Bacterial Proteins; D002352:Carrier Proteins; C093956:HasA protein, Serratia marcescens; C116165:HasR protein, Streptomyces ambofaciens; D006454:Hemoglobins; D008565:Membrane Proteins; D012808:Sigma Factor; D006418:Heme