Curated Optogenetic Publication Database

Abstract: We recently developed a technique for rapidly and reversibly inhibiting protein function through light-inducible sequestration of proteins away from their normal sites of action. Here, we adapt this method for inducible inactivation of Bem1, a scaffold protein involved in budding yeast polarity. We find that acute inhibition of Bem1 produces profound defects in cell polarization and cell viability that are not observed in bem1Δ. By disrupting Bem1 activity at specific points in the cell cycle, we demonstrate that Bem1 is essential for the establishment of polarity and bud emergence but is dispensable for the growth of an emerged bud. By taking advantage of the reversibility of Bem1 inactivation, we show that pole size scales with cell size, and that this scaling is dependent on the actin cytoskeleton. Our experiments reveal how rapid reversible inactivation of protein function complements traditional genetic approaches. This strategy should be widely applicable to other biological contexts.

Abstract: Protein trafficking in and out of the nucleus represents a key step in controlling cell fate and function. Here we report the development of a red light-inducible and far-red light-reversible synthetic system for controlling nuclear localization of proteins in mammalian cells and zebrafish. First, we synthetically reconstructed and validated the red light-dependent Arabidopsis phytochrome B nuclear import mediated by phytochrome-interacting factor 3 in a nonplant environment and support current hypotheses on the import mechanism in planta. On the basis of this principle we next regulated nuclear import and activity of target proteins by the spatiotemporal projection of light patterns. A synthetic transcription factor was translocated into the nucleus of mammalian cells and zebrafish to drive transgene expression. These data demonstrate the first in vivo application of a plant phytochrome-based optogenetic tool in vertebrates and expand the repertoire of available light-regulated molecular devices.

Abstract: Optical dimerizers are a powerful new class of optogenetic tools that allow light-inducible control of protein-protein interactions. Such tools have been useful for regulating cellular pathways and processes with high spatiotemporal resolution in live cells, and a growing number of dimerizer systems are available. As these systems have been characterized by different groups using different methods, it has been difficult for users to compare their properties. Here, we set about to systematically benchmark the properties of four optical dimerizer systems, CRY2/CIB1, TULIPs, phyB/PIF3, and phyB/PIF6. Using a yeast transcriptional assay, we find significant differences in light sensitivity and fold-activation levels between the red light regulated systems but similar responses between the CRY2/CIB and TULIP systems. Further comparison of the ability of the CRY2/CIB1 and TULIP systems to regulate a yeast MAPK signaling pathway also showed similar responses, with slightly less background activity in the dark observed with CRY2/CIB. In the process of developing this work, we also generated an improved blue-light-regulated transcriptional system using CRY2/CIB in yeast. In addition, we demonstrate successful application of the CRY2/CIB dimerizers using a membrane-tethered CRY2, which may allow for better local control of protein interactions. Taken together, this work allows for a better understanding of the capacities of these different dimerization systems and demonstrates new uses of these dimerizers to control signaling and transcription in yeast.

Abstract: Optogenetic gene switches allow gene expression control at an unprecedented spatiotemporal resolution. Recently, light-responsive transgene expression systems that are activated by UV-B, blue, or red light have been developed. These systems perform well on their own, but their integration into genetic networks has been hampered by the overlapping absorbance spectra of the photoreceptors. We identified a lack of orthogonality between UV-B and blue light-controlled gene expression as the bottleneck and employed a model-based approach that identified the need for a blue light-responsive gene switch that is insensitive to low-intensity light. Based on this prediction, we developed a blue light-responsive and rapidly reversible expression system. Finally, we employed this expression system to demonstrate orthogonality between UV-B, blue, and red/far-red light-responsive gene switches in a single mammalian cell culture. We expect this approach to enable the spatiotemporal control of gene networks and to expand the applications of optogenetics in synthetic biology.

Abstract: Light-switchable proteins enable unparalleled control of molecular biological processes in live organisms. Previously, we have engineered red/far-red and green/red photoreversible two-component signal transduction systems (TCSs) with transcriptional outputs in E. coli and used them to characterize and control synthetic gene circuits with exceptional quantitative, temporal, and spatial precision. However, the broad utility of these light sensors is limited by bulky DNA encoding, incompatibility with commonly used ligand-responsive transcription factors, leaky output in deactivating light, and less than 10-fold dynamic range. Here, we compress the four genes required for each TCS onto two streamlined plasmids and replace all chemically inducible and evolved promoters with constitutive, engineered versions. Additionally, we systematically optimize the expression of each sensor histidine kinase and response regulator, and redesign both pathway output promoters, resulting in low leakiness and 72- and 117-fold dynamic range, respectively. These second-generation light sensors can be used to program the expression of more genes over a wider range and can be more easily combined with additional plasmids or moved to different host strains. This work demonstrates that bacterial TCSs can be optimized to function as high-performance sensors for scientific and engineering applications.

Abstract: Optogenetic control of endogenous signaling can be an important tool for probing cell behavior. Using the photoresponse of the LOV2 domain of Avena sativa phototropin 1, we developed analogues of kinase inhibitors whose activity is light dependent. Inhibitory peptides were appended to the Jα helix, where they potently inhibited kinases in the light but were sterically blocked from kinase interaction in the dark. Photoactivatable inhibitors for cyclic-AMP dependent kinase (PKA) and myosin light chain kinase (MLCK) are described, together with studies that shed light on proper positioning of the peptides in the LOV domain. These inhibitors altered endogenous signaling in living cells and produced light-dependent changes in cell morphodynamics.

Abstract: As light-regulated actuators, sensory photoreceptors underpin optogenetics and numerous applications in synthetic biology. Protein engineering has been applied to fine-tune the properties of photoreceptors and to generate novel actuators. For the blue-light-sensitive light-oxygen-voltage (LOV) photoreceptors, mutations near the flavin chromophore modulate response kinetics and the effective light responsiveness. To probe for potential, inadvertent effects on receptor activity, we introduced these mutations into the engineered LOV photoreceptor YF1 and determined their impact on light regulation. While several mutations severely impaired the dynamic range of the receptor (e.g., I39V, R63K, and N94A), residue substitutions in a second group were benign with little effect on regulation (e.g., V28T, N37C, and L82I). Electron paramagnetic resonance and absorption spectroscopy identified correlated effects for certain of the latter mutations on chromophore environment and response kinetics in YF1 and the LOV2 domain from Avena sativa phototropin 1. Carefully chosen mutations provide a powerful means to adjust the light-response function of photoreceptors as demanded for diverse applications.

Abstract: Enormous potential of cell-based therapeutics is hindered by the lack of effective means to control genetically engineered cells in mammalian tissues. Here, we describe a synthetic module for remote photocontrol of engineered cells that can be adapted for such applications. The module involves photoactivated synthesis of cyclic dimeric GMP (c-di-GMP), a stable small molecule that is not produced by higher eukaryotes and therefore is suitable for orthogonal regulation. The key component of the photocontrol module is an engineered bacteriophytochrome diguanylate cyclase, which synthesizes c-di-GMP from GTP in a light-dependent manner. Bacteriophytochromes are particularly attractive photoreceptors because they respond to light in the near-infrared window of the spectrum, where absorption by mammalian tissues is minimal, and also because their chromophore, biliverdin IXα, is naturally available in mammalian cells. The second component of the photocontrol module, a c-di-GMP phosphodiesterase, maintains near-zero background levels of c-di-GMP in the absence of light, which enhances the photodynamic range of c-di-GMP concentrations. In the E. coli model used in this study, the intracellular c-di-GMP levels could be upregulated by light by >50-fold. Various c-di-GMP-responsive proteins and riboswitches identified in bacteria can be linked downstream of the c-di-GMP-mediated photocontrol module for orthogonal regulation of biological activities in mammals as well as in other organisms lacking c-di-GMP signaling. Here, we linked the photocontrol module to a gene expression output via a c-di-GMP-responsive transcription factor and achieved a 40-fold photoactivation of gene expression.

Abstract: Light-dependent dimerization is the basis for recently developed noninvasive optogenetic tools. Here we present a novel tool combining optogenetics with the control of protein kinase activity to investigate signal transduction pathways. Mediated by Arabidopsis thaliana photoreceptor cryptochrome 2, we activated the protein kinase C-RAF by blue light-dependent dimerization, allowing for decoupling from upstream signaling events induced by surface receptors. The activation by light is fast, reversible, and not only time but also dose dependent as monitored by phosphorylation of ERK1/2. Additionally, light-activated C-RAF controls serum response factor-mediated gene expression. Light-induced heterodimerization of C-RAF with a kinase-dead mutant of B-RAF demonstrates the enhancing role of B-RAF as a scaffold for C-RAF activity, which leads to the paradoxical activation of C-RAF found in human cancers. This optogenetic tool enables reversible control of protein kinase activity in signal duration and strength. These properties can help to shed light onto downstream signaling processes of protein kinases in living cells.

Abstract: Apoptosis is a cell death program involved in the development of multicellular organisms, immunity, and pathologies ranging from cancer to HIV/AIDS. We present an engineered protein that causes rapid apoptosis of targeted cells in monolayer culture after stimulation with blue light. Cells transfected with the protein switch L57V, a tandem fusion of the light-sensing LOV2 domain and the apoptosis-executing domain from caspase-7, rapidly undergo apoptosis within 60 min after light stimulation. Constant illumination of under 5 min or oscillating with 1 min exposure had no effect, suggesting that cells have natural tolerance to a short duration of caspase-7 activity. Furthermore, the overexpression of Bcl-2 prevented L57V-mediated apoptosis, suggesting that although caspase-7 activation is sufficient to start apoptosis, it requires mitochondrial contribution to fully commit.