The structural basis for signal promiscuity in a bacterial chemoreceptor Gavira Gallardo, José Antonio Matilla, Miguel A. Fernández Rodríguez, Matilde Krell, Tino Chemoreceptors Chemotaxis Ligand recognition We greatly appreciate the provision of beam time at ALBA and ESRF and the support of the beam-line staff during data collection. This work was supported by FEDER funds and Fondo Social Europeo through grants from the Spanish Ministry for Science, Innovation and Universities to MAM (PID2019-103972GAI00), and the Spanish Ministry of Economy and Competitiveness to JAG (BIO2016-74875-P) and TK (BIO2016-76779-P). Signalling through chemosensory pathways is typically initiated by thebinding of signal molecules to the chemoreceptor ligand binding domain(LBD). The PcaY_PP chemoreceptor from Pseudomonas putida KT2440 ischaracterized by an unusually broad signal range, and minimal requisitesfor signal binding are the presence of a C6-membered ring and that of acarboxyl group. Previous studies have shown that only some of the multi-ple signals recognized by this chemoreceptor are of apparent metabolicvalue. We report here high-resolution structures of PcaY_PP-LBD in theabsence and presence of four cognate chemoeffectors and glycerol. Thedomain formed a four-helix bundle (4HB), and both ligand binding sites ofthe dimer were occupied with the high-affinity ligands protocatechuate andquinate, whereas the lower-affinity ligands benzoate and salicylate werepresent in only one site. Ligand binding was verified by microcalorimetrictitration of site-directed mutants revealing important roles of an arginineand number of polar residues that establish an extensive hydrogen bondingnetwork with bound ligands. The comparison of the apo and holo struc-tures did not provide evidence for this receptor employing a transmem-brane signalling mechanism that involves piston-like shifts of the finalhelix. Instead, ligand binding caused rigid-body scissoring movements ofboth monomers of the dimer. Comparisons with the 4HB domains of theTar and Tsr chemoreceptors revealed significant structural differences.Importantly, the ligand binding site in PcaY_PP-LBD is approximately8 A removed from that of the Tar and Tsr receptors. Data indicate a sig-nificant amount of structural and functional diversity among 4HBdomains. 2026-01-15T11:14:37Z 2026-01-15T11:14:37Z 2021 journal article Gavira JA, Matilla MA, Fernández M, Krell T. The structural basis for signal promiscuity in a bacterial chemoreceptor. FEBS J. 2021 Apr;288(7):2294-2310. doi: 10.1111/febs.15580 2294-2310 https://hdl.handle.net/10481/109743 10.1111/febs.15580 eng http://creativecommons.org/licenses/by-nc-nd/4.0/ open access Attribution-NonCommercial-NoDerivatives 4.0 Internacional Wiley