novel chemoreceptor MCP2983 from Comamonas testosteroni specifically binds to cis-aconitate and triggers chemotaxis towards diverse organic compounds

Comamonas testosteroni CNB-1 behaves chemotactically toward a wide range of organic compounds, and 19 methyl-accepting chemotaxis proteins (MCPs) were annotated from the genome of strain CNB-2, a plasmid-curing derivative from strain CNB-1. The MCP-free mutant CNB-1Δ20 completely lost its chemotactic responses. In this study, we found that a chemoreceptor, namely MCP2983, restored chemotactic responses toward nine carboxylic acids and ten aromatic compounds to CNB-1Δ20. Isothermal titration calorimetry analysis indicated that the ligand-binding domain (LBD) of MCP2983 specifically binds to cis-aconitate but not other tested compounds. Deletion of the LBD of MCP2983 impaired chemotactic responses toward cis-aconitate as well as other tested compounds, indicating that the LBD of MCP2983 was essential for triggering chemotactic responses. Five amino acid residues (M⁸¹, S¹⁵⁶, E¹⁵⁷, I¹⁵⁸, and L¹⁵⁹) that are located at a putative ligand-binding pocket were identified to be involved in binding to cis-aconitate. So far, the MCP2983 represents the sole biochemically identified chemoreceptor that specifically binds to cis-aconitate and is able to trigger chemotaxis towards diverse organic compounds.