Two-component systems (TCS) represent major signal-transduction pathways for adaptation to environmental conditions, and regulate many aspects of bacterial physiology. In the whooping cough agent Bordetella pertussis, the TCS BvgAS controls the virulence regulon, and is therefore critical for pathogenicity. BvgS is a prototypical TCS sensor-kinase with tandem periplasmic Venus flytrap (VFT) domains. VFT are bi-lobed domains that typically close around specific ligands using clamshell motions. We report the X-ray structure of the periplasmic moiety of BvgS, an intricate homodimer with a novel architecture. By combining site-directed mutagenesis, functional analyses and molecular modeling, we show that the conformation of the periplasmic moiety determines the state of BvgS activity. The intertwined structure of the periplasmic portion and the different conformation and dynamics of its mobile, membrane-distal VFT1 domains, and closed, membrane-proximal VFT2 domains, exert a conformational strain onto the transmembrane helices, which sets the cytoplasmic moiety in a kinase-on state by default corresponding to the virulent phase of the bacterium. Signaling the presence of negative signals perceived by the periplasmic domains implies a shift of BvgS to a distinct state of conformation and activity, corresponding to the avirulent phase. The response to negative modulation depends on the integrity of the periplasmic dimer, indicating that the shift to the kinase-off state implies a concerted conformational transition. This work lays the bases to understand virulence regulation in Bordetella. As homologous sensor-kinases control virulence features of diverse bacterial pathogens, the BvgS structure and mechanism may pave the way for new modes of targeted therapeutic interventions.
Bacteria make use of two-component transduction systems, composed of a sensor-kinase and a response regulator, to perceive environmental signals and orchestrate an appropriate response. The virulence regulon of the whooping cough agent Bordetella pertussis is controlled by the two-component system BvgAS. The sensor-kinase BvgS harbor extra-cytoplasmic Venus flytrap perception domains similar to those found in neuronal receptors, and it is the prototype of a large bacterial protein family. We report the atomic structure of the extra-cytoplasmic moiety of BvgS, which shows a novel dimeric arrangement. We show that the virulent phase of B. pertussis that occurs by default corresponds to a specific conformation of BvgS generated by the periplasmic architecture itself and by the differential dynamics of its Venus flytrap domains. The perception of negative signals by the periplasmic domains causes BvgS to shift to a different conformation that corresponds to the avirulent phase of the bacteria. In addition to contributing to our understanding of virulence regulation by B. pertussis at a time of whooping cough re-emergence, this study also paves the way to the mechanistic exploration of the homologous sensor-kinases found in various bacterial pathogens.