Showing 1 - 25 of 48 results
Optoregulated Drug Release from an Engineered Living Material: Self-Replenishing Drug Depots for Long-Term, Light-Regulated Delivery.
On-demand and long-term delivery of drugs are common requirements in many therapeutic applications, not easy to be solved with available smart polymers for drug encapsulation. This work presents a fundamentally different concept to address such scenarios using a self-replenishing and optogenetically controlled living material. It consists of a hydrogel containing an active endotoxin-free Escherichia coli strain. The bacteria are metabolically and optogenetically engineered to secrete the antimicrobial and antitumoral drug deoxyviolacein in a light-regulated manner. The permeable hydrogel matrix sustains a viable and functional bacterial population and permits diffusion and delivery of the synthesized drug to the surrounding medium at quantities regulated by light dose. Using a focused light beam, the site for synthesis and delivery of the drug can be freely defined. The living material is shown to maintain considerable levels of drug production and release for at least 42 days. These results prove the potential and flexibility that living materials containing engineered bacteria can offer for advanced therapeutic applications.
Using Synthetic Biology to Engineer Spatial Patterns.
Synthetic biology has emerged as a multidisciplinary field that provides new tools and approaches to address longstanding problems in biology. It integrates knowledge from biology, engineering, mathematics, and biophysics to build—rather than to simply observe and perturb—biological systems that emulate natural counterparts or display novel properties. The interface between synthetic and developmental biology has greatly benefitted both fields and allowed to address questions that would remain challenging with classical approaches due to the intrinsic complexity and essentiality of developmental processes. This Progress Report provides an overview of how synthetic biology can help to understand a process that is crucial for the development of multicellular organisms: pattern formation. It reviews the major mechanisms of genetically encoded synthetic systems that have been engineered to establish spatial patterns at the population level. Limitations, challenges, applications, and potential opportunities of synthetic pattern formation are also discussed.
Programming Bacteria With Light—Sensors and Applications in Synthetic Biology
Photo-receptors are widely present in both prokaryotic and eukaryotic cells, which serves as the foundation of tuning cell behaviors with light. While practices in eukaryotic cells have been relatively established, trials in bacterial cells have only been emerging in the past few years. A number of light sensors have been engineered in bacteria cells and most of them fall into the categories of two-component and one-component systems. Such a sensor toolbox has enabled practices in controlling synthetic circuits at the level of transcription and protein activity which is a major topic in synthetic biology, according to the central dogma. Additionally, engineered light sensors and practices of tuning synthetic circuits have served as a foundation for achieving light based real-time feedback control. Here, we review programming bacteria cells with light, introducing engineered light sensors in bacteria and their applications, including tuning synthetic circuits and achieving feedback controls over microbial cell culture.
High-resolution Patterned Biofilm Deposition Using pDawn-Ag43.
Spatial structure and patterning play an important role in bacterial biofilms. Here we demonstrate an accessible method for culturing E. coli biofilms into arbitrary spatial patterns at high spatial resolution. The technique uses a genetically encoded optogenetic construct-pDawn-Ag43-that couples biofilm formation in E. coli to optical stimulation by blue light. We detail the process for transforming E. coli with pDawn-Ag43, preparing the required optical set-up, and the protocol for culturing patterned biofilms using pDawn-Ag43 bacteria. Using this protocol, biofilms with a spatial resolution below 25 μm can be patterned on various surfaces and environments, including enclosed chambers, without requiring microfabrication, clean-room facilities, or surface pretreatment. The technique is convenient and appropriate for use in applications that investigate the effect of biofilm structure, providing tunable control over biofilm patterning. More broadly, it also has potential applications in biomaterials, education, and bio-art.
Blue-Light Receptors for Optogenetics.
Sensory photoreceptors underpin light-dependent adaptations of organismal physiology, development, and behavior in nature. Adapted for optogenetics, sensory photoreceptors become genetically encoded actuators and reporters to enable the noninvasive, spatiotemporally accurate and reversible control by light of cellular processes. Rooted in a mechanistic understanding of natural photoreceptors, artificial photoreceptors with customized light-gated function have been engineered that greatly expand the scope of optogenetics beyond the original application of light-controlled ion flow. As we survey presently, UV/blue-light-sensitive photoreceptors have particularly allowed optogenetics to transcend its initial neuroscience applications by unlocking numerous additional cellular processes and parameters for optogenetic intervention, including gene expression, DNA recombination, subcellular localization, cytoskeleton dynamics, intracellular protein stability, signal transduction cascades, apoptosis, and enzyme activity. The engineering of novel photoreceptors benefits from powerful and reusable design strategies, most importantly light-dependent protein association and (un)folding reactions. Additionally, modified versions of these same sensory photoreceptors serve as fluorescent proteins and generators of singlet oxygen, thereby further enriching the optogenetic toolkit. The available and upcoming UV/blue-light-sensitive actuators and reporters enable the detailed and quantitative interrogation of cellular signal networks and processes in increasingly more precise and illuminating manners.
Controlling Cells with Light and LOV.
Optogenetics is a powerful method for studying dynamic processes in living cells and has advanced cell biology research over the recent past. Key to the successful application of optogenetics is the careful design of the light‐sensing module, typically employing a natural or engineered photoreceptor that links the exogenous light input to the cellular process under investigation. Light–oxygen–voltage (LOV) domains, a highly diverse class of small blue light sensors, have proven to be particularly versatile for engineering optogenetic input modules. These can function via diverse modalities, including inducible allostery, protein recruitment, dimerization, or dissociation. This study reviews recent advances in the development of LOV domain‐based optogenetic tools and their application for studying and controlling selected cellular functions. Focusing on the widely employed LOV2 domain from Avena sativa phototropin‐1, this review highlights the broad spectrum of engineering opportunities that can be explored to achieve customized optogenetic regulation. Finally, major bottlenecks in the development of optogenetic methods are discussed and strategies to overcome these with recent synthetic biology approaches are pointed out.
LOV Domains in the Design of Photoresponsive Enzymes.
In nature, a multitude of mechanisms have emerged for regulating biological processes and, specifically, protein activity. Light as a natural regulatory element is of outstanding interest for studying and modulating protein activity because it can be precisely applied with regard to a site of action, instant of time, or intensity. Naturally occuring photoresponsive proteins, predominantly those containing a light-oxygen-voltage (LOV) domain, have been characterized structurally and mechanistically and also conjugated to various proteins of interest. Immediate advantages of these new photoresponsive proteins such as genetic encoding, no requirement of chemical modification, and reversibility are paid by difficulties in predicting the envisaged activity or type and site of domain fusion. In this article, we summarize recent advances and give a survey on currently available design concepts for engineering photoswitchable proteins.
A light-controlled cell lysis system in bacteria.
Intracellular products (e.g., insulin), which are obtained through cell lysis, take up a big share of the biotech industry. It is often time-consuming, laborious, and environment-unfriendly to disrupt bacterial cells with traditional methods. In this study, we developed a molecular device for controlling cell lysis with light. We showed that intracellular expression of a single lysin protein was sufficient for efficient bacterial cell lysis. By placing the lysin-encoding gene under the control of an improved light-controlled system, we successfully controlled cell lysis by switching on/off light: OD600 of the Escherichia coli cell culture was decreased by twofold when the light-controlled system was activated under dark condition. We anticipate that our work would not only pave the way for cell lysis through a convenient biological way in fermentation industry, but also provide a paradigm for applying the light-controlled system in other fields of biotech industry.
Biofilm Lithography enables high-resolution cell patterning via optogenetic adhesin expression.
Bacterial biofilms represent a promising opportunity for engineering of microbial communities. However, our ability to control spatial structure in biofilms remains limited. Here we engineerEscherichia coliwith a light-activated transcriptional promoter (pDawn) to optically regulate expression of an adhesin gene (Ag43). When illuminated with patterned blue light, long-term viable biofilms with spatial resolution down to 25 μm can be formed on a variety of substrates and inside enclosed culture chambers without the need for surface pretreatment. A biophysical model suggests that the patterning mechanism involves stimulation of transiently surface-adsorbed cells, lending evidence to a previously proposed role of adhesin expression during natural biofilm maturation. Overall, this tool-termed "Biofilm Lithography"-has distinct advantages over existing cell-depositing/patterning methods and provides the ability to grow structured biofilms, with applications toward an improved understanding of natural biofilm communities, as well as the engineering of living biomaterials and bottom-up approaches to microbial consortia design.
Optogenetic Control by Pulsed Illumination.
Sensory photoreceptors evoke numerous adaptive responses in Nature and serve as light-gated actuators in optogenetics to enable the spatiotemporally precise, reversible and noninvasive control of cellular events. The output of optogenetic circuits can often be dialed in by varying illumination quality, quantity and duration. Here, we devise a programmable matrix of light-emitting diodes to efficiently probe the response of optogenetic systems to intermittently applied light of varying intensity and pulse frequency. Circuits for light-regulated gene expression markedly differed in their responses to pulsed illumination of a single color which sufficed for sequentially triggering them. In addition to quantity and quality, the pulse frequency of intermittent light hence provides a further input variable for output control in optogenetics and photobiology. Pulsed illumination schemes allow the reduction of overall light dose and facilitate the multiplexing of several light-dependent actuators and reporters.
Light induced expression of β-glucosidase in Escherichia coli with autolysis of cell.
β-Glucosidase has attracted substantial attention in the scientific community because of its pivotal role in cellulose degradation, glycoside transformation and many other industrial processes. However, the tedious and costly expression and purification procedures have severely thwarted the industrial applications of β-glucosidase. Thus development of new strategies to express β-glucosidases with cost-effective and simple procedure to meet the increasing demands on enzymes for biocatalysis is of paramount importance.
Optogenetics Manipulation Enables Prevention of Biofilm Formation of Engineered Pseudomonas aeruginosa on Surfaces.
Synthetic biologists have attempted to solve real-world problems, such as those of bacterial biofilms, that are involved in the pathogenesis of many clinical infections and difficult to eliminate. To address this, we employed a blue light responding system and integrated it into the chromosomes of Pseudomonas aeruginosa. With making rational adaptions and improvements of the light-activated system, we provided a robust and convenient means to spatiotemporally control gene expression and manipulate biological processes with minimal perturbation in P. aeruginosa. It increased the light-induced gene expression up to 20-fold. Moreover, we deliberately introduced a functional protein gene PA2133 containing an EAL domain to degrade c-di-GMP into the modified system, and showed that the optimally engineered optogenetic tool inhibited the formation of P. aeruginosa biofilms through the induction of blue light, resulting in much sparser and thinner biofilms. Our approach establishes a methodology for leveraging the tools of synthetic biology to guide biofilm formation and engineer biofilm patterns with unprecedented spatiotemporal resolution. Furthermore, the findings suggest that the synthetic optogenetic system may provide a promising strategy that could be applied to control and fight biofilms.
Engineering RGB color vision into Escherichia coli.
Optogenetic tools use colored light to rapidly control gene expression in space and time. We designed a genetically encoded system that gives Escherichia coli the ability to distinguish between red, green, and blue (RGB) light and respond by changing gene expression. We use this system to produce 'color photographs' on bacterial culture plates by controlling pigment production and to redirect metabolic flux by expressing CRISPRi guide RNAs.
Engineering genetically-encoded tools for optogenetic control of protein activity.
Optogenetic tools offer fast and reversible control of protein activity with subcellular spatial precision. In the past few years, remarkable progress has been made in engineering photoactivatable systems regulating the activity of cellular proteins. In this review, we discuss general strategies in designing and optimizing such optogenetic tools and highlight recent advances in the field, with specific focus on applications regulating protein catalytic activity.
Time-Resolved X-Ray Solution Scattering Reveals the Structural Photoactivation of a Light-Oxygen-Voltage Photoreceptor.
Light-oxygen-voltage (LOV) receptors are sensory proteins controlling a wide range of organismal adaptations in multiple kingdoms of life. Because of their modular nature, LOV domains are also attractive for use as optogenetic actuators. A flavin chromophore absorbs blue light, forms a bond with a proximal cysteine residue, and induces changes in the surroundings. There is a gap of knowledge on how this initial signal is relayed further through the sensor to the effector module. To characterize these conformational changes, we apply time-resolved X-ray scattering to the homodimeric LOV domain from Bacillus subtilis YtvA. We observe a global structural change in the LOV dimer synchronous with the formation of the chromophore photoproduct state. Using molecular modeling, this change is identified as splaying apart and relative rotation of the two monomers, which leads to an increased separation at the anchoring site of the effector modules.
Optogenetic Modulation of Intracellular Signalling and Transcription: Focus on Neuronal Plasticity.
Several fields in neuroscience have been revolutionized by the advent of optogenetics, a technique that offers the possibility to modulate neuronal physiology in response to light stimulation. This innovative and far-reaching tool provided unprecedented spatial and temporal resolution to explore the activity of neural circuits underlying cognition and behaviour. With an exponential growth in the discovery and synthesis of new photosensitive actuators capable of modulating neuronal networks function, other fields in biology are experiencing a similar re-evolution. Here, we review the various optogenetic toolboxes developed to influence cellular physiology as well as the diverse ways in which these can be engineered to precisely modulate intracellular signalling and transcription. We also explore the processes required to successfully express and stimulate these photo-actuators in vivo before discussing how such tools can enlighten our understanding of neuronal plasticity at the systems level.
Strategies for development of optogenetic systems and their applications.
It has become clear that biological processes are highly dynamic and heterogeneous within and among cells. Conventional analytical tools and chemical or genetic manipulations are unsuitable for dissecting the role of their spatiotemporally dynamic nature. Recently, optical control of biomolecular signaling, a technology called “optogenetics,” has gained much attention. The technique has enabled spatial and temporal regulation of specific signaling pathways both in vitro and in vivo. This review presents strategies for optogenetic systems development and application for biological research. Combinations with other technologies and future perspectives are also discussed herein. Although many optogenetic approaches are designed to modulate ion channel conductivity, we mainly examine systems that target other biomolecular reactions such as gene expression, protein translocations, and kinase or receptor signaling pathways.
An extraordinary stringent and sensitive light-switchable gene expression system for bacterial cells.
Light-switchable gene expression systems provide transient, non-invasive and reversible means to control biological processes with high tunability and spatiotemporal resolution. In bacterial cells, a few light-regulated gene expression systems based on photoreceptors and two-component regulatory systems (TCSs) have been reported, which respond to blue, green or red light.
Library-Aided Probing of Linker Determinants in Hybrid Photoreceptors.
Signaling proteins comprise interaction and effector modules connected by linkers. Throughout evolution, these recurring modules have multiply been recombined to produce the present-day plethora of signaling proteins. Likewise, modular recombination lends itself to the engineering of hybrid signal receptors, whose functionality hinges on linker topology, sequence, and length. Often, numerous linkers must be assessed to obtain functional receptors. To expedite linker optimization, we devised the PATCHY strategy (primer-aided truncation for the creation of hybrid proteins) for the facile construction of hybrid gene libraries with defined linker distributions. Empowered by PATCHY, we engineered photoreceptors whose signal response was governed by linker length: whereas blue-light-repressed variants possessed linkers of 7n or 7n+5 residues, variants with 7n+1 residues were blue-light-activated. Related natural receptors predominantly displayed linker lengths of 7n and 7n+5 residues but rarely of 7n+1 residues. PATCHY efficiently explores linker sequence space to yield functional hybrid proteins including variants transcending the natural repertoire of signaling proteins.
A proposal for a dipole-generated BLUF domain mechanism.
The resting and signaling structures of the blue-light sensing using flavin (BLUF) photoreceptor domains are still controversially debated due to differences in the molecular models obtained by crystal and NMR structures. Photocycles for the given preferred structural framework have been established, but a unifying picture combining experiment and theory remains elusive. We summarize present work on the AppA BLUF domain from both experiment and theory. We focus on IR and UV/vis spectra, and to what extent theory was able to reproduce experimental data and predict the structural changes upon formation of the signaling state. We find that the experimental observables can be theoretically reproduced employing any structural model, as long as the orientation of the signaling essential Gln63 and its tautomer state are a choice of the modeler. We also observe that few approaches are comparative, e.g., by considering all structures in the same context. Based on recent experimental findings and a few basic calculations, we suggest the possibility for a BLUF activation mechanism that only relies on electron transfer and its effect on the local electrostatics, not requiring an associated proton transfer. In this regard, we investigate the impact of dispersion correction on the interaction energies arising from weakly bound amino acids.
A critical element of the light-induced quaternary structural changes in YtvA-LOV.
YtvA, a photosensory LOV (light-oxygen-voltage) protein from Bacillus subtilis, exists as a dimer that previously appeared to undergo surprisingly small structural changes after light illumination compared with other light-sensing proteins. However, we now report that light induces significant structural perturbations in a series of YtvA-LOV domain derivatives in which the Jα helix has been truncated or replaced. Results from native gel analysis showed significant mobility changes in these derivatives after light illumination; YtvA-LOV without the Jα helix dimerized in the dark state but existed as a monomer in the light state. The absence of the Jα helix also affected the dark regeneration kinetics and the stability of the flavin mononucleotide (FMN) binding to its binding site. Our results demonstrate an alternative way of photo-induced signal propagation that leads to a bigger functional response through dimer/monomer conversions of the YtvA-LOV than the local disruption of Jα helix in the As-LOV domain.
Optimizing optogenetic constructs for control over signaling and cell behaviours.
Optogenetic tools have recently been developed that enable dynamic control over the activities of select signaling proteins. They provide the unique ability to rapidly turn signaling events on or off with subcellular control in living cells and organisms. This capability is leading to new insights into how the spatial and temporal coordination of signaling events governs dynamic cell behaviours such as migration and neurite outgrowth. These tools can also be used to dissect a protein's signaling functions at different organelles. Here we review the properties of photoreceptors from diverse organisms that have been leveraged to control signaling in mammalian cells. We emphasize recent engineering approaches that have been used to create optogenetic constructs with optimized spectral, kinetic, and signaling properties for controlling cell behaviours.
Applications of hydrogen deuterium exchange (HDX) for the characterization of conformational dynamics in light-activated photoreceptors.
Rational design of optogenetic tools is inherently linked to the understanding of photoreceptor function. Structural analysis of elements involved in signal integration in individual sensor domains provides an initial idea of their mode of operation, but understanding how local structural rearrangements eventually affect signal transmission to output domains requires inclusion of the effector regions in the characterization. However, the dynamic nature of these assemblies renders their structural analysis challenging and therefore a combination of high- and low-resolution techniques is required to appreciate functional aspects of photoreceptors. This review focuses on the potential of hydrogen-deuterium exchange coupled to mass spectrometry (HDX-MS) for complementing the structural characterization of photoreceptors. In this respect, the ability of HDX-MS to provide information on conformational dynamics and the possibility to address multiple functionally relevant states in solution render this methodology ideally suitable. We highlight recent examples demonstrating the potential of HDX-MS and discuss how these results can help to improve existing optogenetic systems or guide the design of novel optogenetic tools.
Sensory photoreceptors not only control diverse adaptive responses in Nature, but as light-regulated actuators they also provide the foundation for optogenetics, the non-invasive and spatiotemporally precise manipulation of cellular events by light. Novel photoreceptors have been engineered that establish control by light over manifold biological processes previously inaccessible to optogenetic intervention. Recently, photoreceptor engineering has witnessed a rapid development, and light-regulated actuators for the perturbation of a plethora of cellular events are now available. Here, we review fundamental principles of photoreceptors and light-regulated allostery. Photoreceptors dichotomize into associating receptors that alter their oligomeric state as part of light-regulated allostery and non-associating receptors that do not. A survey of engineered photoreceptors pinpoints light-regulated association reactions and order-disorder transitions as particularly powerful and versatile design principles. Photochromic photoreceptors that are bidirectionally toggled by two light colors augur enhanced spatiotemporal resolution and use as photoactivatable fluorophores. By identifying desirable traits in engineered photoreceptors, we provide pointers for the design of future, light-regulated actuators.
LOV-based optogenetic devices: light-driven modules to impart photoregulated control of cellular signaling.
The Light-Oxygen-Voltage domain family of proteins is widespread in biology where they impart sensory responses to signal transduction domains. The small, light responsive LOV modules offer a novel platform for the construction of optogenetic tools. Currently, the design and implementation of these devices is partially hindered by a lack of understanding of how light drives allosteric changes in protein conformation to activate diverse signal transduction domains. Further, divergent photocycle properties amongst LOV family members complicate construction of highly sensitive devices with fast on/off kinetics. In the present review we discuss the history of LOV domain research with primary emphasis on tuning LOV domain chemistry and signal transduction to allow for improved optogenetic tools.