J. these residues reduced affinities (2- to 345-fold) for both agonistic and antagonistic compounds. Our data indicate that determining the inhibitory activity of antagonists is a potentially fruitful alternative to design specific two-component system inhibitors for the development of new drugs to inhibit processes regulated by two-component systems. promotor (13C16). The architecture of the 108-kDa HPK TodS is atypical and complex. TodS offers two supradomains, each comprising a periodic circadian-Ah receptor single-minded protein (PAS) sensor website and a histidine kinase website (Fig. 1), which are separated by an RR receiver website. TodS lacks transmembrane areas and is therefore likely to be located in the cytosol (8, 13). The N-terminal PAS website of TodS binds PSFL toluene with high affinity ((14). TodS seems to belong to a subfamily of HPKs involved in the control of catabolic pathways for the degradation of solvents. For example, TmoS (82% identity with TodS) settings toluene degradation from the T4MO pathway in (17), TutC (49% identity) regulates the anaerobic degradation of toluene in sp. strain T1 (18), and StyS (41% identity) in sp. strain Y2 is definitely involved in styrene degradation (19). Open in a separate windowpane Fig. 1. Website corporation of TodS. The NTodS and CTodS recombinant proteins are indicated. Agonists and antagonists bind to the PAS-1 website. PAS, PAS-type sensor website; HK, histidine kinase website; RRR, response regulator receiver website. In the present study, 5-Hydroxypyrazine-2-Carboxylic Acid we used isothermal titration calorimetry (ITC) to measure the thermodynamic guidelines for the binding of a wide range of different compounds to purified TodS. We then related these data to the capacity of these compounds to induce gene expression and to their ability to activate TodS autophosphorylation activity Ligand Affinities of TodS and the Capacity of the Compounds to Induce Gene Manifestation was determined by measuring the -gal activity having a Pfusion. The binding guidelines and -gal measurements are outlined in Table 1. Table 1. thermodynamic guidelines for the binding of different hydrocarbons to TodS and their capacity to induce manifestation from P(Table 1). Nitro-, chloro-, and fluorobenzene bound to TodS with affinities in the low micromolar range and were found to be potent inducers of manifestation from P(Table 1). Benzamide and benzoate were not bound by TodS, which is definitely consistent with their failure to induce gene manifestation axis. Derived thermodynamic data are given in Table 1. Taking into consideration that toluene is an efficient inducer and Table 1), but only activity, whereas (Table 1). To further verify these findings, we investigated the interaction of the three toluidines (amino toluenes). Again, than the additional two isomers (Table 1), although it bound to TodS more tightly than response without exerting a significant impact on binding affinity. This apparent lack of correlation between the affinity measured and expression studies was further confirmed by the fact the second-best inducer 5-Hydroxypyrazine-2-Carboxylic Acid affinity (does not automatically translate into 5-Hydroxypyrazine-2-Carboxylic Acid induction by a compound and don’t activate gene manifestation but show no activity. Agonists and Antagonists Bind to the Same PAS Website. We then analyzed the mode of action of antagonists, among which and the genes in pMIR66 were carried out to determine whether this competition was observed (Fig. 3). In parallel experiments, the -gal activity in cultures induced with toluene was compared with cultures to which by DOT-T1E harboring pMIR66 (comprising fusion) were cultivated in LB to a turbidity of 0.2 at 660 nm. Then, six 5-Hydroxypyrazine-2-Carboxylic Acid cultures were exposed to by replacing the wild-type allele in pMIR66 with the mutant variants and measuring induction from Pas -gal. As expected,.