Light Signaling and Allostery Mechanisms of a Dual-sensor Photoreceptor

PPHK (phosphorylation-responsive photosensitive histidine kinase) from Leptolyngbya sp. JSC-1 is a dual sensor kinase that integrates upstream phosphorylation and red-light signals via a molecular logic "OR". As a member of the phytochrome superfamily, PPHK undergoes reversible photoconversion between green light-absorbing (Pg) and red light-absorbing (Pr) states. Its modular architecture, with a dimeric scaffold typical of sensory histidine kinases, makes it an excellent model for studying allosteric activation and signal integration. Using cryoelectron microscopy (cryoEM), I determined the full-length structure of PPHK at near-atomic resolution in different signaling states, providing key insights into the structural basis of allosteric regulation and signal integration in modular signaling proteins. This dissertation uncovers how photoreceptors and sensory histidine kinases process environmental signals, offering new perspectives on signal transduction mechanisms.