Figure 1
The QS signaling cascade of Vibrio harveyi . (A) In V. harveyi the AIs HAI-1, CAI-1 and AI-2 are synthesized by LuxM, CqsA and LuxS respectively, and are detected by the hybrid sensor kinases LuxN, CqsS and LuxQ (with its binding protein LuxP). The higher the AI concentration, the lower the autophosphorylation activity of the kinases [24]. Dashed lines marked with a ‘P’ indicate phosphotransfer reactions. H (histidine) and D (aspartate) denote phosphorylation sites. CM, cytoplasmic membrane; CP, cytoplasm; PP, periplasm. (B) In the absence of AIs, the phosphoryl group is transferred by phosphorelay via the histidine phosphotransfer protein LuxU to the σ54-dependent transcriptional activator LuxO. Phosphorylated LuxO activates transcription of five regulatory sRNAs (Qrr1-5), four of which, together with the chaperone Hfq, destabilize the mRNA for the master regulator LuxR. (C) In the presence of AIs, LuxO is dephosphorylated, and LuxR is produced. LuxR activates genes responsible for bioluminescence, biofilm formation and exoproteolytic activity, and represses genes involved in type III secretion and siderophore production