Role of dimer asymmetry in signaling of blue-light sensor histidine kinases

Photoreceptor sensory histidine kinases (SHKs) enable bacteria to sense and respond to light and serve as key optogenetic components, yet the structural mechanism linking light absorption to enzymatic activation remains unclear. We recently engineered dimeric SHKs based on short LOV domains from P. putida, fusing SB1 or SB2 to the DHp–CA effector module of FixL. Crystal structures of SB2F1 showed a symmetric, light-like conformation in both dark and illuminated states, whereas solution SAXS and functional assays revealed large, light-dependent rearrangements. We propose that LOV-SHKs switch between symmetric (kinase-active) and asymmetric (phosphatase-active) states. This proposal aims to use time-resolved SAXS on SB2F1 to track light-induced structural changes on seconds-to-minutes timescales and define the kinetics linking LOV photoactivation to kinase signaling. Results will provide the first dynamic view of SHK signaling and principles for engineering new light-responsive systems.