Bacteria mount internal alarms to escape or adapt to environmental change. These alarms change bacterial swimming direction (chemotaxis), surface (twitching) motility, gene expression, biofilm formation and the course of infection. Exact responses are species-specific but they are all modulated by chemosensory systems that consist of sensory receptors (chemoreceptors) and effector proteins. The chemosensory system we study contains a chemoreceptor called Aer-2 that is found in a number of pathogens including Pseudomonas aeruginosa and Vibrio cholerae. Aer-2 receptors contain PAS sensing domains, a common domain in nature that is used to bind cofactors and monitor various cellular conditions. The PAS domains of Aer-2 (one in PaAer-2 and two in VcAer-2) bind heme and respond to several diatomic oxy-gases. In the case of PaAer-2, upstream and downstream di-HAMP domains control the signaling state of the receptor in response to PAS signaling. In the case of VcAer-2, a duplicated N-terminal PAS-heme domain may serve a similar role to the N-terminal di-HAMP domain of PaAer-2. My lab is currently working to understand the steps from PAS-ligand binding, to PAS/HAMP and HAMP/HAMP signaling, the output response of the receptors and the resulting changes in bacterial behavior. In the example of Aer-2 receptors, we propose that this series of events are important for bacterial pathogenesis.
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