Biology subjects

Meier, S. S. M.

Publications and source records attributed to Meier, S. S. M..

3 recordsLinked to original sources

bioRxiv2025

Dimer asymmetry in signaling of blue-light sensor histidine kinases

Photoreceptor sensory histidine kinases (SHKs) couple light absorption to conformational changes regulating two-component signaling. Despite their importance and widespread use in optogenetics, the underlying structural signaling mechanisms remain poorly understood. We here engineered dimeric SHKs based on Pseudomonas putida short light-oxygen-voltage (LOV) proteins and determined their crystal structures. Regardless of illumination, the structures adopted a light-state like LOV-LOV dimer with symmetric/straight kinase modules. In contrast, small-angle X-ray scattering together with functional assays revealed pronounced light-dependent rearrangements in solution and allowed the assignment of the kinase-ON dark state to an asymmetric/kinked conformation, whereas the light state adopts a symmetric/straight structure. Comparative analyses of natural and engineered SHKs identified conserved motifs linking LOV domain rotation to kinase activity. The findings highlight the central role of dimer asymmetry and flexibility in SHK signaling, thereby not least informing the engineering of new light-responsive signaling systems.

biochemistry↗

bioRxiv2025

Traits of Bathy Phytochromes and Application to Bacterial Optogenetics

Phytochromes are photoreceptors sensitive to red and far-red light found in a wide variety of organisms, including plants, fungi, and bacteria. Bacteriophytochromes (BphPs) can be switched between a red light-sensitive Pr state and a far-red light-sensitive Pfr state by illumination. In so-called prototypical BphPs, the Pr state functions as the thermally favoured resting state, whereas Pfr is more stable in bathy BphPs. The prototypical DrBphP from Deinococcus radiodurans has been shown to be compatible with different output module types. Even though red light regulated optogenetic tools are available, like the pREDusk system based on the DrBphP photosensory module, far-red light-modulated variants are still rare. Here, we study the underlying contributors to bathy over prototypical BphP behaviour by way of various chimeric constructs between pREDusk and representative bathy BphPs. We pinpoint shared traits of the otherwise heterogenous subgroup of bathy BphPs, and highlight the importance of the sensor-effector linker in light modulation of histidine kinase activity. Informed by these data, we introduce the far-red light-activated system "pFREDusk", based on a histidine kinase activity governed by a bathy photosensory module. With this tool, we expand the optogenetic toolbox into wavelengths of increased sample and tissue penetration.

biochemistry↗

bioRxiv2025

Engineering NIR-Sighted Bacteria

Spatially and temporally orchestrated gene expression underpins organismal development, physiology, and adaptation. In bacteria, two-component systems (TCS) translate environmental cues into inducible expression outputs. Inducible expression also serves as a versatile instrument in both basic and applied science. Here, we harness the photosensors of rhizobial bathy-phytochromes to construct synthetic TCSs for stringent activation of gene expression by near-infrared (NIR) light in laboratory and probiotic Escherichia coli strains, and in Agrobacterium tumefaciens. Orthogonal TCSs afford the multiplexed expression control of several genes by NIR and visible light. Notwithstanding substantial photochemical activation of bathy-phytochromes by visible radiation, the NIR-light-responsive systems hardly responded to red light. Evidently, light signals can be processed by TCSs into highly nonlinear responses at the physiological relevant level of gene expression. These fundamental aspects likely extend to naturally occurring TCSs. Depending on their photosensor traits and environmental conditions, bathy-phytochromes may thus either be NIR-specific or function as colorblind receptors of light vs. darkness.

biochemistry↗