Multiple solute binding proteins for gamma-aminobutyrate and
5-aminovalerate in Pseudomonas aeruginosa : assessment of their
potential role in sensor kinase activation
Abstract
The canonical mode of receptor activation consists in the binding of
signals or signal-loaded solute binding proteins (SBPs) to sensor
domains. Many sensor histidine kinases (SHK), that are activated by SBP
binding, are encoded next to their cognate sbp gene. To assess to what
degree this is a general rule, we studied three SBPs of Pseudomonas
aeruginosa PAO1 that are encoded in the vicinity of genes encoding the
AgtS (PA0600) and AruS (PA4982) SHKs. Ligand screening using compound
libraries and microcalorimetric studies showed that the SPBs PA0602 and
PA4985 both bound preferentially GABA (KD=2.3 and 0.58 microM,
respectively), followed by 5-aminovalerate (KD=30 and 1.6 microM,
respectively) and ethanoldiamine (KD=2.3 and 0.58 microM, respectively),
whereas AgtB (PA0604) recognized exclusively 5-aminovaleric acid (KD=2.9
microM). However, microcalorimetric titrations of the AgtS sensor domain
with AgtB or PA0602 in the absence or presence of ligands did not reveal
binding. By analogy, bacterial two-hybrid assays failed to show an
interaction of PA4985 with the AruS-sensor domain. Vicinal sbp and shk
genes are thus not always functionally linked. We previously identified
PA0222 as a GABA-specific SBP. The existence of three SBPs for GABA may
be related to the role of GABA as an inducer of P. aeruginosa virulence.