Chemotactic-signal transducers respond to changes in the concentration of attractants and repellents in the environment, transduce a signal from the outside to the inside of the cell, and facilitate sensory adaptation through the variation of the level of methylation. Responds to L-His, L-Pro and gamma-aminobutyrate (GABA). Also involved in repellent responses to trichloroethylene (TCE), chloroform and methylthiocyanate (PubMed:16233808, PubMed:23650915, PubMed:9353923). Also mediates chemotaxis to histamine, but does not bind histamine (PubMed:30425146). The ligand binding region binds directly to 2 L-amino acids (PubMed:23650915). Binding of GABA induces structural changes of the chemoreceptor (PubMed:31964737). Mutant shows no defect in chemotaxis toward L-amino acids. Mutant shows also decreased chemotactic responses to TCE, chloroform and methylthiocyanate (PubMed:16233808, PubMed:9353923). Deletion of pctA, pctB and pctC abolishes chemotaxis to 5 mM histamine, but significant chemotaxis is observed at a concentration range between 500 nM and 500 uM (PubMed:30425146). The pctABC-tlpQ deletion mutant is devoid of histamine chemotaxis over the entire concentration range (50 nM to 50 mM) (PubMed:30425146). The deletion mutant does not show significant reduction in swarming or immobilization near epithelial wounds, but the pctABC triple deletion mutant shows a significant reduction in chemotaxis and immobilization along wounds of human cystic fibrosis airway epithelial cells (PubMed:27031335). PctA has a broad ligand range and responds to most of the proteinogenic amino acids, whereas PctB and PctC have a much narrower range and show strong ligand preference for L-glutamine and gamma-aminobutyrate, respectively. These receptors are paralogs: pctA gene duplication in the common ancestor of the genus Pseudomonas led to pctC, whereas pctB originated through another, independent pctA duplication. Belongs to the methyl-accepting chemotaxis (MCP) protein family.