Two different mechanisms mediate chemotaxis to inorganic phosphate in Pseudomonas aeruginosa

Abstract

Inorganic phosphate (Pi) is a central signaling molecule that modulates virulence in various pathogens. In Pseudomonas aeruginosa, low Pi concentrations induce transcriptional alterations that increase virulence. Also, under low Pi levels, P. aeruginosa exhibits Pi chemotaxis—a process mediated by the two non-paralogous receptors CtpH and CtpL. Here we show that the two receptors operate via different mechanisms. We demonstrate that the ligand binding domain (LBD) of CtpH but not CtpL binds Pi directly. We identify the periplasmic ligand binding protein PstS as the protein that binds in its Pi loaded state to CtpL, resulting in receptor stimulation. PstS forms part of the Pi transporter and has thus a double function in Pi transport and chemotaxis. The affinity of Pi for CtpH was modest whereas that for PstS very high, which may explain why CtpH and CtpL mediate chemotaxis to high and low Pi concentrations, respectively. The pstS/ctpH double mutant was almost devoid of Pi taxis, indicating that PstS is the only CtpL Pi-shuttle. Chemotaxis mechanisms based on indirect ligand recognition were unambiguously identified in enterobacteria. The discovery of a similar mechanism in a different bacterial order, involving a different chemoreceptor type and chemoeffector suggests that such systems are widespread.

The ligand‐binding domain of a chemoreceptor from Comamonas testosteroni has a previously unknown homotrimeric structure

“…The individual LBD of Tar exists in a dynamic equilibrium between monomers and dimers and ligand binding induces dimerization since the ligand interacts with both monomers to stabilize the dimer (Milligan and Koshland, ; Yeh et al , ; Biemann and Koshland, ; Yeh et al , ). Similar to Tar, some other helical LBDs also alter the oligomeric state upon ligand binding, such as 4HB domains of PcaY_PP (Fernandez et al , ) and CtpH (Rico‐Jimenez et al , ), HBM domains of McpS (Lacal et al , ) and McpQ (Martin‐Mora et al , ), and PilJ domain of McpN (Martin‐Mora et al , ). On the contrary, the oligomerization of some dCACHE and sCACHE LBDs is not altered by ligand binding and their ligand binding sites are not located at the dimeric interface (Rico‐Jimenez et al , ; Martin‐Mora et al , ; Gavira et al , ).…”

Identification of a Chemoreceptor in Pseudomonas aeruginosa That Specifically Mediates Chemotaxis Toward α-Ketoglutarate

“…In particular its responses to amino acids by the three paralogous receptors PctA, PctB, and PctC (Kuroda et al, 1995; Taguchi et al, 1997; Rico-Jimenez et al, 2013; McKellar et al, 2015; Reyes-Darias et al, 2015a,b) as well as its response to inorganic phosphate (Wu et al, 2000; Rico-Jimenez et al, 2016) by the CtpL and CtpH receptors have been studied in some depth. In addition, the cytosolic and atypical receptor McpB (also named Aer2) (Watts et al, 2011; Airola et al, 2013; Garcia-Fontana et al, 2014; Garcia et al, 2016) was subject to many studies and is amongst the best studied members of the chemoreceptor sub-family with cytoplasmic location.…”

“…One of them, CtpL, was found to mediate specifically chemotaxis to low Pi concentrations (Wu et al, 2000). However, CtpL does not bind Pi directly but recognizes the Pi loaded periplasmic binding protein PstS (Rico-Jimenez et al, 2016). The remaining two receptors, PA1646 and PA5072, are of unknown function.…”

Assigning chemoreceptors to chemosensory pathways inPseudomonas aeruginosa

“…pathways, correspondingly. Ten chemoreceptors-PctA, PctB, PctC (25,26), CtpH, CtpL (27,28), TlpQ (29), McpA (30), PA2652 (31), McpS (32), and McpK (33)-were implicated in chemotaxis. However, there is only limited experimental evidence that permits their assignment to the major (Che I/F6) chemotaxis pathway.…”