Molecular Insights into Toluene Sensing in the TodS/TodT Signal Transduction System

Abstract

TodS is a sensor kinase that responds to various monoaromatic compounds, which either cause an agonistic or antagonistic effect on phosphorylation of its cognate response regulator TodT, and controls tod operon expression in Pseudomonas putida strains. We describe a molecular sensing mechanism of TodS that is activated in response to toluene. The crystal structures of the TodS Per-Arnt-Sim (PAS) 1 sensor domain (residues 43–164) and its complex with toluene (agonist) or 1,2,4-trimethylbenzene (antagonist) show a typical β2α3β3 PAS fold structure (residues 45–149), forming a hydrophobic ligand-binding site. A signal transfer region (residues 150–163) located immediately after the canonical PAS fold may be intrinsically flexible and disordered in both apo-PAS1 and antagonist-bound forms and dramatically adapt an α-helix upon toluene binding. This structural change in the signal transfer region is proposed to result in signal transmission to activate the TodS/TodT two-component signal transduction system. Site-directed mutagenesis and β-galactosidase assays using a P. putida reporter strain system verified the essential residues involved in ligand sensing and signal transfer and suggest that the Phe46 residue acts as a ligand-specific switch.

Transcriptional Regulation of the Peripheral Pathway for the Anaerobic Catabolism of Toluene and m-Xylene in Azoarcus sp. CIB

“…It is worth noting that the amino acid residues shown to be involved in the binding to the inducer in the PAS1 domain of TodS, i.e., Phe46, Ile74, Phe79 and Ile114, are conserved in PAS1 domains of other TodS family members but not in any of the PAS domains of TdiS-like proteins. This observation is in agreement with the fact that TodS family members recognize aromatic hydrocarbons as inducers ( Busch et al, 2007 ; Busch et al, 2009 ; Koh et al, 2016 ) but TdiS-like histidine kinases may respond to an intermediate, i.e., a benzylsuccinate derivative, rather than to the precursor aromatic hydrocarbon.…”

“…According to their primary structure and molecular architecture, the sensor histidine kinases of these two-component regulatory systems can be classified in at least three different phylogenetic groups, i.e., the TodS, TdiS and BphS groups ( Figure 7A ). Hybrid histidine kinases of the TodS family are complex enzymes that contain two sensor PAS domains, i.e., PAS1, that recognizes aromatic hydrocarbons ( Busch et al, 2007 ), and PAS2, involved in dimerization ( Koh et al, 2016 ), two transmitter (autokinase) domains, and a response regulator receiver domain ( Figure 7A ) ( Busch et al, 2009 ). They are involved in the control of the genes for the aerobic degradation of toluene in Pseudomonas putida (TodS) ( Busch et al, 2007 ), P. mendocina (TmoS) ( Silva-Jiménez et al, 2012 ) and, probably, in T. aromatica (TutC) ( Leuthner and Heider, 1998 ), and styrene in some Pseudomonas strains (StyS) ( Velasco et al, 1998 ; Leoni et al, 2003 ).…”

Crystal structure of the Vibrio cholerae VqmA–ligand–DNA complex provides insight into ligand-binding mechanisms relevant for drug design

“…4 and Fig. S1) (22)(23)(24)(25). However, although the overall folds of the PAS region were similar, the precise positions of various structural elements differed substantially, especially in the regions controlling ligand specificity ( Fig.…”

“…By contrast, it has some conservative regions compared with other PAS proteins (Fig. 4), such as PYP of Halorhodospira halophile, which plays a role as a light sensor in the photocycle by binding a chromophore (24); ThkA of Thermotoga maritima, which might be responsible for the interaction of TrrA with the ThkA DHp domain (25); FixL of Bradyrhizobium diazoefficiens, which acts as an important oxygen sensor (23,37); and TodS of Pseudomonas putida, which is a sensor kinase that responds to various monoaromatic compounds (22). This structural information implies that the PAS of VqmA plays a role as a sensor and delivers the signal to the DBD by DPO-induced structural rearrangements, thereby regulating its DNA-binding activity.…”

New family of biosensors for monitoring BTX in aquatic and edaphic environments

“…Our bioreporter system is based on the two component regulatory system TodS–TodT of P. putida DOT‐T1E, and the P todX promoter fused to the GFP protein as a reporter protein. It was previously determined that toluene was the best inducer of the P todX promoter and that this induction was controlled by the sensor kinase, TodS, that phosphorylates its cognate response regulator, TodT (Lacal et al ., ; Busch et al ., , ; Silva‐Jiménez et al ., ; Koh et al ., ). For the construction of different biosensors that would be functional in different environments such as soils and fresh and marine waters, this bioreporter was transferred into three different bacterial strains that were isolated from three different environments.…”