FIG 5.
Model of quorum sensing regulation of chitobiose utilization genes in V. cholerae. When V. cholerae grows on a chitinous surface, the periplasmic chitin binding protein (CBP) binds to chitin oligosaccharides. This derepresses ChiS, which can then activate expression of the chitobiose utilization operon (chb) through recruitment of RNA polymerase (RNAP) (10). Binding of SlmA to Pchb is also required for transcriptional activation (11). (A) At low CAI-1 concentrations, the CqsS sensor indirectly (dashed line) promotes LuxO phosphorylation, which indirectly blocks HapR expression. In this state, Pchb is maximally expressed. (B) At high CAI-1 concentrations, the CqsS sensor indirectly dephosphorylates LuxO, which results in indirect activation of HapR expression. HapR then exerts a repressive effect on Pchb by decreasing expression of this locus ∼2-fold in the presence of the ClpAP protease machine. If HapR is not degraded by ClpAP, its repressive effect can result in an ∼7-fold decrease in Pchb expression. The mechanism of HapR repression may be through occluding binding of SlmA or RNAP to Pchb.