Showing 1 - 25 of 35 results
Synthetic Biological Approaches for Optogenetics and Tools for Transcriptional Light‐Control in Bacteria.
Light has become established as a tool not only to visualize and investigate but also to steer biological systems. This review starts by discussing the unique features that make light such an effective control input in biology. It then gives an overview of how light‐control came to progress, starting with photoactivatable compounds and leading up to current genetic implementations using optogenetic approaches. The review then zooms in on optogenetics, focusing on photosensitive proteins, which form the basis for optogenetic engineering using synthetic biological approaches. As the regulation of transcription provides a highly versatile means for steering diverse biological functions, the focus of this review then shifts to transcriptional light regulators, which are presented in the biotechnologically highly relevant model organism Escherichia coli.
Optical regulation of endogenous RhoA reveals switching of cellular responses by signal amplitude.
Precise control of the timing and amplitude of protein activity in living cells can explain how cells compute responses to complex biochemical stimuli. The small GTPase RhoA can promote either focal adhesion (FA) growth or cell edge retraction, but how a cell chooses between these opposite outcomes is poorly understood. Here, we developed a photoswitchable RhoA guanine exchange factor (psRhoGEF) to obtain precise optical control of endogenous RhoA activity. We find that low levels of RhoA activation by psRhoGEF induces edge retraction and FA disassembly, while high levels of RhoA activation induces both FA growth and disassembly. We observed that mDia-induced Src activation at FAs occurs preferentially at lower levels of RhoA activation. Strikingly, inhibition of Src causes a switch from FA disassembly to growth. Thus, rheostatic control of RhoA activation reveals how cells use signal amplitude and biochemical context to select between alternative responses to a single biochemical signal.
Single-Molecule Analysis and Engineering of DNA Motors.
Molecular motors are diverse enzymes that transduce chemical energy into mechanical work and, in doing so, perform critical cellular functions such as DNA replication and transcription, DNA supercoiling, intracellular transport, and ATP synthesis. Single-molecule techniques have been extensively used to identify structural intermediates in the reaction cycles of molecular motors and to understand how substeps in energy consumption drive transitions between the intermediates. Here, we review a broad spectrum of single-molecule tools and techniques such as optical and magnetic tweezers, atomic force microscopy (AFM), single-molecule fluorescence resonance energy transfer (smFRET), nanopore tweezers, and hybrid techniques that increase the number of observables. These methods enable the manipulation of individual biomolecules via the application of forces and torques and the observation of dynamic conformational changes in single motor complexes. We also review how these techniques have been applied to study various motors such as helicases, DNA and RNA polymerases, topoisomerases, nucleosome remodelers, and motors involved in the condensation, segregation, and digestion of DNA. In-depth analysis of mechanochemical coupling in molecular motors has made the development of artificially engineered motors possible. We review techniques such as mutagenesis, chemical modifications, and optogenetics that have been used to re-engineer existing molecular motors to have, for instance, altered speed, processivity, or functionality. We also discuss how single-molecule analysis of engineered motors allows us to challenge our fundamental understanding of how molecular motors transduce energy.
Optogenetics sheds new light on tissue engineering and regenerative medicine.
Optogenetics has demonstrated great potential in the fields of tissue engineering and regenerative medicine, from basic research to clinical applications. Spatiotemporal encoding during individual development has been widely identified and is considered a novel strategy for regeneration. A as a noninvasive method with high spatiotemporal resolution, optogenetics are suitable for this strategy. In this review, we discuss roles of dynamic signal coding in cell physiology and embryonic development. Several optogenetic systems are introduced as ideal optogenetic tools, and their features are compared. In addition, potential applications of optogenetics for tissue engineering are discussed, including light-controlled genetic engineering and regulation of signaling pathways. Furthermore, we present how emerging biomaterials and photoelectric technologies have greatly promoted the clinical application of optogenetics and inspired new concepts for optically controlled therapies. Our summation of currently available data conclusively demonstrates that optogenetic tools are a promising method for elucidating and simulating developmental processes, thus providing vast prospects for tissue engineering and regenerative medicine applications.
Light-induced dimerization approaches to control cellular processes.
Light-inducible approaches provide means to control biological systems with spatial and temporal resolution that is unmatched by traditional genetic perturbations. Recent developments of optogenetic and chemo-optogenetic systems for induced proximity in cells facilitate rapid and reversible manipulation of highly dynamic cellular processes and have become valuable tools in diverse biological applications. The new expansions of the toolbox facilitate control of signal transduction, genome editing, 'painting' patterns of active molecules onto cellular membranes and light-induced cell cycle control. A combination of light- and chemically induced dimerization approaches has also seen interesting progress. Here we provide an overview of the optogenetic systems and the emerging chemo-optogenetic systems, and discuss recent applications in tackling complex biological problems.
A yeast system for discovering optogenetic inhibitors of eukaryotic translation initiation.
The precise spatiotemporal regulation of protein synthesis is essential for many complex biological processes such as memory formation, embryonic development and tumor formation. Current methods used to study protein synthesis offer only a limited degree of spatiotemporal control. Optogenetic methods, in contrast, offer the prospect of controlling protein synthesis non-invasively within minutes and with a spatial scale as small as a single synapse. Here, we present a hybrid yeast system where growth depends on the activity of human eukaryotic initiation factor 4E (eIF4E) that is suitable for screening optogenetic designs for the down-regulation of protein synthesis. We used this system to screen a diverse initial panel of 15 constructs designed to couple a light switchable domain (PYP, RsLOV, LOV, Dronpa) to 4EBP2 (eukaryotic initiation factor 4E binding protein 2), a native inhibitor of translation initiation. We identified cLIPS1 (circularly permuted LOV inhibitor of protein synthesis 1), a fusion of a segment of 4EBP2 and a circularly permuted version of the LOV2 domain from Avena sativa, as a photo-activated inhibitor of translation. Adapting the screen for higher throughput, we tested small libraries of cLIPS1 variants and found cLIPS2, a construct with an improved degree of optical control. We show that these constructs can both inhibit translation in yeast harboring a human eIF4E in vivo, and bind human eIF4E in vitro in a light-dependent manner. This hybrid yeast system thus provides a convenient way for discovering optogenetic constructs that can regulate of human eIF4E-depednednt translation initiation in a mechanistically defined manner.
Optically inducible membrane recruitment and signaling systems.
Optical induction of intracellular signaling by membrane-associated and integral membrane proteins allows spatiotemporally precise control over second messenger signaling and cytoskeletal rearrangements that are important to cell migration, development, and proliferation. Optogenetic membrane recruitment of a protein-of-interest to control its signaling by altering subcellular localization is a versatile means to these ends. Here, we summarize the signaling characteristics and underlying structure-function of RGS-LOV photoreceptors as single-component membrane recruitment tools that rapidly, reversibly, and efficiently carry protein cargo from the cytoplasm to the plasma membrane by a light-regulated electrostatic interaction with the membrane itself. We place the technology-relevant features of these recently described natural photosensory proteins in context of summarized protein engineering and design strategies for optically controlling membrane protein signaling.
Controlling protein conformation with light.
Optogenetics, genetically encoded engineering of proteins to respond to light, has enabled precise control of the timing and localization of protein activity in live cells and for specific cell types in animals. Light-sensitive ion channels have become well established tools in neurobiology, and a host of new methods have recently enabled the control of other diverse protein structures as well. This review focuses on approaches to switch proteins between physiologically relevant, naturally occurring conformations using light, accomplished by incorporating light-responsive engineered domains that sterically and allosterically control the active site.
Photodimerization systems for regulating protein-protein interactions with light.
Optogenetic dimerizers are modular domains that can be utilized in a variety of versatile ways to modulate cellular biochemistry. Because of their modularity, many applications using these tools can be easily transferred to new targets without extensive engineering. While a number of photodimerizer systems are currently available, the field remains nascent, with new optimizations for existing systems and new approaches to regulating biological function continuing to be introduced at a steady pace.
Perspectives of RAS and RHEB GTPase Signaling Pathways in Regenerating Brain Neurons.
Cellular activation of RAS GTPases into the GTP-binding "ON" state is a key switch for regulating brain functions. Molecular protein structural elements of rat sarcoma (RAS) and RAS homolog protein enriched in brain (RHEB) GTPases involved in this switch are discussed including their subcellular membrane localization for triggering specific signaling pathways resulting in regulation of synaptic connectivity, axonal growth, differentiation, migration, cytoskeletal dynamics, neural protection, and apoptosis. A beneficial role of neuronal H-RAS activity is suggested from cellular and animal models of neurodegenerative diseases. Recent experiments on optogenetic regulation offer insights into the spatiotemporal aspects controlling RAS/mitogen activated protein kinase (MAPK) or phosphoinositide-3 kinase (PI3K) pathways. As optogenetic manipulation of cellular signaling in deep brain regions critically requires penetration of light through large distances of absorbing tissue, we discuss magnetic guidance of re-growing axons as a complementary approach. In Parkinson's disease, dopaminergic neuronal cell bodies degenerate in the substantia nigra. Current human trials of stem cell-derived dopaminergic neurons must take into account the inability of neuronal axons navigating over a large distance from the grafted site into striatal target regions. Grafting dopaminergic precursor neurons directly into the degenerating substantia nigra is discussed as a novel concept aiming to guide axonal growth by activating GTPase signaling through protein-functionalized intracellular magnetic nanoparticles responding to external magnets.
A bright future: optogenetics to dissect the spatiotemporal control of cell behavior.
Cells sense, process, and respond to extracellular information using signaling networks: collections of proteins that act as precise biochemical sensors. These protein networks are characterized by both complex temporal organization, such as pulses of signaling activity, and by complex spatial organization, where proteins assemble structures at particular locations and times within the cell. Yet despite their ubiquity, studying these spatial and temporal properties has remained challenging because they emerge from the entire protein network rather than a single node, and cannot be easily tuned by drugs or mutations. These challenges are being met by a new generation of optogenetic tools capable of directly controlling the activity of individual signaling nodes over time and the assembly of protein complexes in space. Here, we outline how these recent innovations are being used in conjunction with engineering-influenced experimental design to address longstanding questions in signaling biology.
Optogenetic Medicine: Synthetic Therapeutic Solutions Precision-Guided by Light.
Gene- and cell-based therapies are well recognized as central pillars of next-generation medicine, but controllability remains a critical issue for clinical applications. In this context, optogenetics is opening up exciting new opportunities for precision-guided medicine by using illumination with light of appropriate intensity and wavelength as a trigger signal to achieve pinpoint spatiotemporal control of cellular activities, such as transgene expression. In this review, we highlight recent advances in optogenetics, focusing on devices for biomedical applications. We introduce the construction and applications of optogenetic-based biomedical tools to treat neurological diseases, diabetes, heart diseases, and cancer, as well as bioelectronic implants that combine light-interfaced electronic devices and optogenetic systems into portable personalized precision bioelectronic medical tools. Optogenetics-based technology promises the capability to achieve traceless, remotely controlled precision dosing of an enormous range of therapeutic outputs. Finally, we discuss the prospects for optogenetic medicine, as well as some emerging challenges.
Optogenetic Tools for Subcellular Applications in Neuroscience.
The ability to study cellular physiology using photosensitive, genetically encoded molecules has profoundly transformed neuroscience. The modern optogenetic toolbox includes fluorescent sensors to visualize signaling events in living cells and optogenetic actuators enabling manipulation of numerous cellular activities. Most optogenetic tools are not targeted to specific subcellular compartments but are localized with limited discrimination throughout the cell. Therefore, optogenetic activation often does not reflect context-dependent effects of highly localized intracellular signaling events. Subcellular targeting is required to achieve more specific optogenetic readouts and photomanipulation. Here we first provide a detailed overview of the available optogenetic tools with a focus on optogenetic actuators. Second, we review established strategies for targeting these tools to specific subcellular compartments. Finally, we discuss useful tools and targeting strategies that are currently missing from the optogenetics repertoire and provide suggestions for novel subcellular optogenetic applications.
Applications of optobiology in intact cells and multi-cellular organisms.
Temporal kinetics and spatial coordination of signal transduction in cells are vital for cell fate determination. Tools that allow for precise modulation of spatiotemporal regulation of intracellular signaling in intact cells and multicellular organisms remain limited. The emerging optobiological approaches use light to control protein-protein interaction in live cells and multicellular organisms. Optobiology empowers light-mediated control of diverse cellular and organismal functions such as neuronal activity, intracellular signaling, gene expression, cell proliferation, differentiation, migration, and apoptosis. In this review, we highlight recent developments in optobiology, focusing on new features of second-generation optobiological tools. We cover applications of optobiological approaches in the study of cellular and organismal functions, discuss current challenges, and present our outlook. Taking advantage of the high spatial and temporal resolution of light control, optobiology promises to provide new insights into the coordination of signaling circuits in intact cells and multicellular organisms.
Genetically Encoded Photoactuators and Photosensors for Characterization and Manipulation of Pluripotent Stem Cells.
Our knowledge of pluripotent stem cell biology has advanced considerably in the past four decades, but it has yet to deliver on the great promise of regenerative medicine. The slow progress can be mainly attributed to our incomplete understanding of the complex biologic processes regulating the dynamic developmental pathways from pluripotency to fully-differentiated states of functional somatic cells. Much of the difficulty arises from our lack of specific tools to query, or manipulate, the molecular scale circuitry on both single-cell and organismal levels. Fortunately, the last two decades of progress in the field of optogenetics have produced a variety of genetically encoded, light-mediated tools that enable visualization and control of the spatiotemporal regulation of cellular function. The merging of optogenetics and pluripotent stem cell biology could thus be an important step toward realization of the clinical potential of pluripotent stem cells. In this review, we have surveyed available genetically encoded photoactuators and photosensors, a rapidly expanding toolbox, with particular attention to those with utility for studying pluripotent stem cells.
Synthetic biological approaches to optogenetically control cell signaling.
Precise spatial and temporal control of cellular processes is in life sciences a highly sought-after capability. In the recent years, this goal has become progressively achievable through the field of optogenetics, which utilizes light as a non-invasive means to control genetically encoded light-responsive proteins. The latest optogenetic systems, such as those for control of subcellular localization or cellular decision-making and tissue morphogenesis provide us with insights to gain a deeper understanding of the cellular inner workings. Besides, they hold a potential for further development into biomedical applications, from in vitro optogenetics-assisted drug candidate screenings to light-controlled gene therapy and tissue engineering.
The rise of photoresponsive protein technologies applications in vivo: a spotlight on zebrafish developmental and cell biology.
The zebrafish ( Danio rerio) is a powerful vertebrate model to study cellular and developmental processes in vivo. The optical clarity and their amenability to genetic manipulation make zebrafish a model of choice when it comes to applying optical techniques involving genetically encoded photoresponsive protein technologies. In recent years, a number of fluorescent protein and optogenetic technologies have emerged that allow new ways to visualize, quantify, and perturb developmental dynamics. Here, we explain the principles of these new tools and describe some of their representative applications in zebrafish.
Optical control of cell signaling by single-chain photoswitchable kinases.
Protein kinases transduce signals to regulate a wide array of cellular functions in eukaryotes. A generalizable method for optical control of kinases would enable fine spatiotemporal interrogation or manipulation of these various functions. We report the design and application of single-chain cofactor-free kinases with photoswitchable activity. We engineered a dimeric protein, pdDronpa, that dissociates in cyan light and reassociates in violet light. Attaching two pdDronpa domains at rationally selected locations in the kinase domain, we created the photoswitchable kinases psRaf1, psMEK1, psMEK2, and psCDK5. Using these photoswitchable kinases, we established an all-optical cell-based assay for screening inhibitors, uncovered a direct and rapid inhibitory feedback loop from ERK to MEK1, and mediated developmental changes and synaptic vesicle transport in vivo using light.
Optogenetics - Bringing light into the darkness of mammalian signal transduction.
Cells receive many different environmental clues to which they must adapt accordingly. Therefore, a complex signal transduction network has evolved. Cellular signal transduction is a highly dynamic process, in which the specific outcome is a result of the exact spatial and temporal resolution of single sub-events. While conventional techniques, like chemical inducer systems, have led to a sound understanding of the architecture of signal transduction pathways, the spatiotemporal aspects were often impossible to resolve. Optogenetics, based on genetically encoded light-responsive proteins, has the potential to revolutionize manipulation of signal transduction processes. Light can be easily applied with highest precision and minimal invasiveness. This review focuses on examples of optogenetic systems which were generated and applied to manipulate non-neuronal mammalian signaling processes at various stages of signal transduction, from cell membrane through cytoplasm to nucleus. Further, the future of optogenetic signaling will be discussed.
The Growing and Glowing Toolbox of Fluorescent and Photoactive Proteins.
Over the past 20 years, protein engineering has been extensively used to improve and modify the fundamental properties of fluorescent proteins (FPs) with the goal of adapting them for a fantastic range of applications. FPs have been modified by a combination of rational design, structure-based mutagenesis, and countless cycles of directed evolution (gene diversification followed by selection of clones with desired properties) that have collectively pushed the properties to photophysical and biochemical extremes. In this review, we provide both a summary of the progress that has been made during the past two decades, and a broad overview of the current state of FP development and applications in mammalian systems.
Optogenetic Immunomodulation: Shedding Light on Antitumor Immunity.
Microbial opsin-based optogenetic tools have been transformative for neuroscience. To extend optogenetic approaches to the immune system to remotely control immune responses with superior spatiotemporal precision, pioneering tools have recently been crafted to modulate lymphocyte trafficking, inflammasome activation, dendritic cell (DC) maturation, and antitumor immunity through the photoactivation of engineered chemokine receptors and calcium release-activated calcium channels. We highlight herein some conceptual design strategies for installing light sensitivities into the immune signaling network and, in parallel, we propose potential solutions for in vivo optogenetic applications in living organisms with near-infrared light-responsive upconversion nanomaterials. Moreover, to move beyond proof-of-concept into translational applications, we discuss future prospects for integrating personalized immunoengineering with optogenetics to overcome critical hurdles in cancer immunotherapy.
Following Optogenetic Dimerizers and Quantitative Prospects.
Optogenetics describes the use of genetically encoded photosensitive proteins to direct intended biological processes with light in recombinant and native systems. While most of these light-responsive proteins were originally discovered in photosynthetic organisms, the past few decades have been punctuated by experiments that not only commandeer but also engineer and enhance these natural tools to explore a wide variety of physiological questions. In addition, the ability to tune dynamic range and kinetic rates of optogenetic actuators is a challenging question that is heavily explored with computational methods devised to facilitate optimization of these systems. Here, we explain the basic mechanisms of a few popular photodimerizing optogenetic systems, discuss applications, compare optogenetic tools against more traditional chemical methods, and propose a simple quantitative understanding of how actuators exert their influence on targeted processes.
Modular engineering of cellular signaling proteins and networks.
Living cells respond to their environment using networks of signaling molecules that act as sensors, information processors, and actuators. These signaling systems are highly modular at both the molecular and network scales, and much evidence suggests that evolution has harnessed this modularity to rewire and generate new physiological behaviors. Conversely, we are now finding that, following nature's example, signaling modules can be recombined to form synthetic tools for monitoring, interrogating, and controlling the behavior of cells. Here we highlight recent progress in the modular design of synthetic receptors, optogenetic switches, and phospho-regulated proteins and circuits, and discuss the expanding role of combinatorial design in the engineering of cellular signaling proteins and networks.
Chromophore Structure of Photochromic Fluorescent Protein Dronpa: Acid-Base Equilibrium of Two Cis Configurations.
Dronpa is a novel photochromic fluorescent protein that exhibits fast response to light. The present article is the first report of the resonance and preresonance Raman spectra of Dronpa. We used the intensity and frequency of Raman bands to determine the structure of the Dronpa chromophore in two thermally stable photochromic states. The acid-base equilibrium in one photochromic state was observed by spectroscopic pH titration. The Raman spectra revealed that the chromophore in this state shows a protonation/deprotonation transition with a pKa of 5.2 ± 0.3 and maintains the cis configuration. The observed resonance Raman bands showed that the other photochromic state of the chromophore is in a trans configuration. The results demonstrate that Raman bands selectively enhanced for the chromophore yield valuable information on the molecular structure of the chromophore in photochromic fluorescent proteins after careful elimination of the fluorescence background.
Investigating neuronal function with optically controllable proteins.
In the nervous system, protein activities are highly regulated in space and time. This regulation allows for fine modulation of neuronal structure and function during development and adaptive responses. For example, neurite extension and synaptogenesis both involve localized and transient activation of cytoskeletal and signaling proteins, allowing changes in microarchitecture to occur rapidly and in a localized manner. To investigate the role of specific protein regulation events in these processes, methods to optically control the activity of specific proteins have been developed. In this review, we focus on how photosensory domains enable optical control over protein activity and have been used in neuroscience applications. These tools have demonstrated versatility in controlling various proteins and thereby cellular functions, and possess enormous potential for future applications in nervous systems. Just as optogenetic control of neuronal firing using opsins has changed how we investigate the function of cellular circuits in vivo, optical control may yet yield another revolution in how we study the circuitry of intracellular signaling in the brain.