Light-Regulated Sensor Histidine Kinases - Structure, Dynamics & Optogenetics

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Signal receptors comprise sensor modules which are responsive to chemical or physical stimuli and effector modules which possess biological activity. Interactions between sensor and effector are at the very basis of the signal-dependent modulation of biological activity, and a comprehensive biochemical, biophysical and structural characterization must involve intact sensor-effector entities. Our focus is on sensory photoreceptors which serve as lightregulated actuators in optogenetics. By employing the engineered light-oxygen-voltage photoreceptor YF1 as a paradigm, we capitalize on the dark-adapted structure of the full-length protein we recently determined. We seek to elucidate the conformational and dynamic transitions underpinning signal transduction and how they lead to regulation of effector activity. Structural information on the light-adapted state and reaction intermediates will be obtained by X-ray crystallography. In parallel, we will probe the dynamics of signal transduction by a combination of functional assays, electron paramagnetic resonance, infrared spectroscopy and hydrogen-deuterium exchange. Guided by molecular dynamics simulations, structural and dynamic data will be reconciled to reveal how photosensor and effector communicate. Structural and mechanistic principles evidenced in YF1 recur in diverse signaling proteins. An improved understanding of fundamental aspects of signal transduction will thus benefit the rational engineering of photoreceptors and their optogenetic deployment.