Signal production and detection specificity in Vibrio CqsA/CqsS quorum-sensing systems.
Bottom Line: However, a phenylalanine is present at this position in Vibrio harveyi CqsS and other homologues, suggesting that a shorter CAI-1-like molecule functions as the signal.We isolated CqsS mutants in each species that display reversed specificity for ligands.Our analysis provides insight into how fidelity is maintained in signal transduction systems.
Affiliation: Department of Molecular Biology, Princeton University, Princeton, NJ, USA.Show MeSH
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Mentions: The CqsS receptor is conserved among many Vibrio species. Notably, the transmembrane ligand-sensing domains share more than 70% amino acid sequence identity. This high sequence identity suggests that CqsS receptors could recognize a common or a related set of signalling molecules. (S)-3-hydroxytridecan-4-one and (S)-3-aminotridecan-4-one (i.e. CAI-1 and Am-CAI-1, respectively, Fig. 1A) are two potent 13-carbon CqsS agonists produced and detected by V. cholerae (Higgins et al., 2007; Kelly et al., 2009). We previously showed that a single amino acid change in the CqsS-sensing domain results in an altered ligand specificity (Ng et al., 2010). Specifically, replacing Cys 170 with a bulky amino acid causes a loss in response to CAI-1 and an increase in sensitivity to a CAI-1 analogue carrying a shortened 8-carbon tail (C8-CAI-1, Fig. 1A) (Ng et al., 2010). We inspected all CqsS receptor homologues in sequenced Vibrios and found that many of them, including the V. harveyi CqsS, carry a phenylalanine substitution at this particular position (Fig. 2A). Therefore, we suspect that these receptors must detect molecules that are shorter than CAI-1.
Affiliation: Department of Molecular Biology, Princeton University, Princeton, NJ, USA.