The first component in a typical bacterial two-component signaling pathway is a multi-domain sensory histidine kinase (HK) that perceives and converts a variety of environmental signals to biological signals. Many prokaryotic photoreceptors are such sensory HKs that undergo light-dependent autophosphorylation of its HK domain. Despite a plethora of biochemical and structural studies, how sensory HKs achieve allosteric regulation in a modular architecture remains elusive, primarily due to lack of sufficient structural information on these highly dynamic full-length signaling proteins. To understand the structural basis of allosteric activation, we study a dual-sensor bilin-based photoreceptor PPHK from cyanobacterium <i>Leptolyngbya</i>sp. JSC-1 (Gan et al., 2014; Rockwell et al., 2015). With a covalently attached phycocyanobilin chromophore, PPHK undergoes reversible photoconversion between the green light-absorbing (Pg) state and red light-absorbing (Pr) state. We have demonstrated that PPHK confers the molecular logic OR in response to a phosphorylation signal and a light signal (Shin et al., 2019). Using cryo-electron microscopy and crystallography, we aim to determine the full-length structures of PPHK and dissect its modes of action in different signaling states. Recent results from our structural and biochemical studies will be presented. Findings of this work will provide structural insights into the molecular mechanism of allosteric regulation and the roles of dimer asymmetry in modular photoreceptors.

Deciphering the structural basis of molecular logic in dual-sensor photoreceptor PPHK

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ACS Fall 2022

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