title: Identification of a chemoreceptor for tricarboxylic acid cycle intermediates: differential chemotactic response towards receptor ligands.
abstract: We report the identification of McpS as the specific chemoreceptor for 6 tricarboxylic acid (TCA) cycle intermediates and butyrate in Pseudomonas putida. The analysis of the bacterial mutant deficient in mcpS and complementation assays demonstrate that McpS is the only chemoreceptor of TCA cycle intermediates in the strain under study. TCA cycle intermediates are abundantly present in root exudates, and taxis toward these compounds is proposed to facilitate the access to carbon sources. McpS has an unusually large ligand-binding domain (LBD) that is un-annotated in InterPro and is predicted to contain 6 helices. The ligand profile of McpS was determined by isothermal titration calorimetry of purified recombinant LBD (McpS-LBD). McpS recognizes TCA cycle intermediates but does not bind very close structural homologues and derivatives like maleate, aspartate, or tricarballylate. This implies that functional similarity of ligands, such as being part of the same pathway, and not structural similarity is the primary element, which has driven the evolution of receptor specificity. The magnitude of chemotactic responses toward these 7 chemoattractants, as determined by qualitative and quantitative chemotaxis assays, differed largely. Ligands that cause a strong chemotactic response (malate, succinate, and fumarate) were found by differential scanning calorimetry to increase significantly the midpoint of protein unfolding (T(m)) and unfolding enthalpy (DeltaH) of McpS-LBD. Equilibrium sedimentation studies show that malate, the chemoattractant that causes the strongest chemotactic response, stabilizes the dimeric state of McpS-LBD. In this respect clear parallels exist to the Tar receptor and other eukaryotic receptors, which are discussed.
authors.affiliation: Department of Environmental Protection, Estación Experimental del Zaidín, CSIC, 18008 Granada, Spain.
authors.forename: Jesús
authors.initials: J
authors.lastname: Lacal
authors.forename: Carlos
authors.initials: C
authors.lastname: Alfonso
authors.forename: Xianxian
authors.initials: X
authors.lastname: Liu
authors.forename: Rebecca E
authors.initials: RE
authors.lastname: Parales
authors.forename: Bertrand
authors.initials: B
authors.lastname: Morel
authors.forename: Francisco
authors.initials: F
authors.lastname: Conejero-Lara
authors.forename: Germán
authors.initials: G
authors.lastname: Rivas
authors.forename: Estrella
authors.initials: E
authors.lastname: Duque
authors.forename: Juan L
authors.initials: JL
authors.lastname: Ramos
authors.forename: Tino
authors.initials: T
authors.lastname: Krell
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism*; D001667:Binding, Competitive; D002087:Butyrates / Q000378:metabolism; D002633:Chemotaxis; D002952:Citric Acid Cycle; D008024:Ligands; D008293:Malates / Q000378:metabolism; D055503:Protein Multimerization; D055550:Protein Stability; D020836:Protein Structure, Quaternary; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D016958:Pseudomonas putida / Q000166:cytology* / Q000378:metabolism*; D013379:Substrate Specificity; D019802:Succinic Acid / Q000378:metabolism; D013696:Temperature; D013816:Thermodynamics
chemical_list: D001426:Bacterial Proteins; D002087:Butyrates; D008024:Ligands; D008293:Malates; C030298:malic acid; D019802:Succinic Acid