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Photosynthesis is a fundamental process that converts photons into chemical energy, driven by large protein complexes at the thylakoid membranes of plants, cyanobacteria, and algae. In plants, water-soluble plastocyanin (Pc) is responsible for shuttling electrons between cytochrome b6f complex and the photosystem I (PSI) complex in the photosynthetic electron transport chain (PETC). For an efficient turnover, a transient complex must form between PSI and Pc in the PETC, which implies a balance between specificity and binding strength. Here, we studied the binding frequency and the unbinding force between suitably oriented plant PSI and Pc under redox control using single molecule force spectroscopy (SMFS). The binding frequency (observation of binding-unbinding events) between PSI and Pc depends on their respective redox states. The interaction between PSI and Pc is independent of the redox state of PSI when Pc is reduced, and it is disfavored in the dark (reduced P700) when Pc is oxidized. The frequency of interaction between PSI and Pc is higher when at least one of the partners is in a redox state ready for electron transfer (ET), and the post-ET situation (PSIRed-PcOx) leads to lower binding. In addition, we show that the binding of ET-ready PcRedto PSI can be regulated externally by Mg2+ions in solution.

The interest in the photochromism and functional applications of donor-acceptor Stenhouse adducts (DASAs) soared in recent years owing to their outstanding advantages and flexible design. However, their low solubility and irreversible conversion in aqueous solutions hampered exploring DASAs for biology and medicine. It is notably unknown whether the barbiturate electron acceptor group retains the pharmacological activity of drugs such as phenobarbital, which targets γ-aminobutyric acid (GABA)-type A receptors (GABAARs) in the brain. Here, we have developed the model compound DASA-barbital based on a scaffold of red-switching second-generation DASAs, and we demonstrate that it is active in GABAARs and alters the neuronal firing rate in a physiological medium at neutral pH. DASA-barbital can also be reversibly photoswitched in acidic aqueous solutions using cyclodextrin, an approved ingredient of drug formulations. These findings clarify the path toward the biological applications of DASAs and to exploit the versatility displayed in polymers and materials science.

Charge exchange is the fundamental process that sustains cellular respiration and photosynthesis by shuttling electrons in a cascade of electron transfer (ET) steps between redox cofactors. While intraprotein charge exchange is well characterized in protein complexes bearing multiple redox sites, interprotein processes are less understood due to the lack of suitable experimental approaches and the dynamic nature of the interactions. Proteins constrained between electrodes are known to support electron transport (ETp) through the protein matrix even without redox cofactors, as the charges housed by redox sites in ET are furnished by the electrodes in ETp configuration. However, it is unknown whether protein ETp mechanisms apply to the interprotein medium that is present in physiological conditions. Here, we study interprotein charge exchange between plant photosystem I (PSI) and its soluble redox partner plastocyanin (Pc) and address the role of the Pc copper center. Using electrochemical scanning tunnelling spectroscopy (ECSTS) current-distance and blinking measurements we respectively quantify the spatial span of charge exchange between individual Pc/PSI pairs and ETp through transient Pc/PSI complexes. Pc devoid of the redox center (Pcapo) can exchange charge with PSI and it does so at longer distances than with the copper ion (Pcholo). Conductance bursts associated to Pcapo/PSI complex formation are higher than in Pcholo/PSI. Thus, copper ions are not required for long distance ETp between PSI and Pc but regulate its spatial span and conductance. Our results suggest that the redox center that carries the charge in Pc is not necessary to exchange it in interprotein ET through the aqueous solution, and question the canonical view of tight complex binding between redox protein partners.

Ratiometric fluorescent nanothermometers with near-infrared emission play an important role in in vivo sensing since they can be used as intracellular thermal sensing probes with high spatial resolution and high sensitivity, to investigate cellular functions of interest in diagnosis and therapy, where current approaches are not effective. Herein, the temperature-dependent fluorescence of organic nanoparticles is designed, synthesized, and studied based on the dual emission, generated by monomer and excimer species, of the tris(2,4,6-trichlorophenyl)methyl radical (TTM) doping organic nanoparticles (TTMd-ONPs), made of optically neutral tris(2,4,6-trichlorophenyl)methane (TTM-αH), acting as a matrix. The excimer emission intensity of TTMd-ONPs decreases with increasing temperatures whereas the monomer emission is almost independent and can be used as an internal reference. TTMd-ONPs show a great temperature sensitivity (3.4% K-1 at 328 K) and a wide temperature response at ambient conditions with excellent reversibility and high colloidal stability. In addition, TTMd-ONPs are not cytotoxic and their ratiometric outputs are unaffected by changes in the environment. Individual TTMd-ONPs are able to sense temperature changes at the nano-microscale. In vivo thermometry experiments in Caenorhabditis elegans (C. elegans) worms show that TTMd-ONPs can locally monitor internal body temperature changes with spatio-temporal resolution and high sensitivity, offering multiple applications in the biological nanothermometry field.© 2023 The Authors. Small published by Wiley-VCH GmbH.

The transduction of odorant binding into cellular signaling by olfactory receptors (ORs) is not understood and knowing its mechanism would enable developing new pharmacology and biohybrid electronic detectors of volatile organic compounds bearing high sensitivity and selectivity. The electrical characterization of ORs in bulk experiments is subject to microscopic models and assumptions. We have directly determined the nanoscale electrical properties of ORs immobilized in a fixed orientation, and their change upon odorant binding, using electrochemical scanning tunneling microscopy (EC-STM) in near-physiological conditions. Recordings of current versus time, distance, and electrochemical potential allows determining the OR impedance parameters and their dependence with odorant binding. Our results allow validating OR structural-electrostatic models and their functional activation processes, and anticipating a novel macroscopic biosensor based on ORs.

Altres ajuts: CERCA Programme/Generalitat de Catalunya, Fundaluce and "la Caixa" foundations (ID 100010434, agreement LCF/PR/HR19/52160010), Co-financed by the European Union Regional Development Fund within the framework of the ERDF Operational Program of Catalonia 2014-2020 Adrenoceptors are ubiquitous and mediate important autonomic functions as well as modulating arousal, cognition, and pain on a central level. Understanding these physiological processes and their underlying neural circuits requires manipulating adrenergic neurotransmission with high spatio-temporal precision. Here we present a first generation of photochromic ligands (adrenoswitches) obtained via azologization of a class of cyclic amidines related to the known ligand clonidine. Their pharmacology, photochromism, bioavailability, and lack of toxicity allow for broad biological applications, as demonstrated by controlling locomotion in zebrafish and pupillary responses in mice.

Understanding the dopaminergic system is a priority in neurobiology and neuropharmacology. Dopamine receptors are involved in the modulation of fundamental physiological functions, and dysregulation of dopaminergic transmission is associated with major neurological disorders. However, the available tools to dissect the endogenous dopaminergic circuits have limited specificity, reversibility, resolution, or require genetic manipulation. Here, we introduce azodopa, a novel photoswitchable ligand that enables reversible spatiotemporal control of dopaminergic transmission. We demonstrate that azodopa activates D1-like receptors in vitro in a light-dependent manner. Moreover, it enables reversibly photocontrolling zebrafish motility on a timescale of seconds and allows separating the retinal component of dopaminergic neurotransmission. Azodopa increases the overall neural activity in the cortex of anesthetized mice and displays illumination-dependent activity in individual cells. Azodopa is the first photoswitchable dopamine agonist with demonstrated efficacy in wild-type animals and opens the way to remotely controlling dopaminergic neurotransmission for fundamental and therapeutic purposes. This research was funded by EU Horizon 2020 Framework Programme for Research and Innovation: Human Brain Project WaveScalES, Specific Grant Agreement 2 No. 785907 and Specific Grant Agreement 3 No. 945539; NEUROPA project, Grant Agreement No. 863214; DEEPER project ICT-36-2020-101016787; European Union Regional Development Fund within the framework of the ERDF Operational Program of Catalonia 2014-2020: CECH project; Ministry of Science and Innovation DEEP RED grant PID2019-111493RB-I00 funded by MCIN/AEI/10.13039/501100011033; Ministerio de Economía y Competitividad and European Regional Development Funds: Grant no. SAF2017-87629-R to V.C., SAF2016-80726-R to M.V.P., SAF2017-88076-R to M.M.; AGAUR/Generalitat de Catalunya: CERCA Programme; Generalitat de Catalunya: Grant no. 2017-SGR-1442 to P.G., 2017-SGR-1497 to V.C., 2017-SGR-210 to M.V.P., and 2017-SGR-00465 to J.H.; Fundaluce and “la Caixa” foundations: ID 100010434, grant agreement LCF/PR/HR19/52160010.

The interest in the photochromism and functional applications of donor-acceptor Stenhouse adducts (DASAs) soared in recent years, owing to their outstanding advantages and flexible design. However, their low solubility and irreversible conversion in aqueous solutions hampered exploring DASAs for biology and medicine. It is notably unknown whether the barbiturate electron acceptor group retains the pharmacological activity of drugs like phenobarbital, which targets γ-aminobutyric acid (GABA) type A receptors (GABAARs) in the brain. Here, we have developed the model compound DASA-barbital based on a scaffold of red-switching second-generation DASAs and we demonstrate that it is active in GABAARs and alters the neuronal firing rate in a physiological medium at neutral pH. DASA-barbital can also be reversibly photoswitched in acidic aqueous solutions using cyclodextrin, an approved ingredient of drug formulations. These findings clear the path towards the biological applications of DASAs and to exploit the versatility displayed in polymers and materials science.

It has been recently shown that electron transfer (ET) between mitochondrial cytochrome c (Cc) and the cytochrome c1 subunit of the cytochrome bc1 (Cc1) and Cc can proceed at long-distance through the aqueous solution. Cc is thought to adjust its activity by changing the affinity for its partners via Tyr48 phosphorylation, but it is unknown how it impacts the nanoscopic environment, interaction forces, and long-range ET. Here, we constrain the orientation and separation between Cc1 and Cc or the phosphomimetic Y48pCMF Cc, and deploy an array of single-molecule, bulk, and computational methods to investigate the molecular mechanism of ET regulation by Cc phosphorylation.. We demonstrate that phosphorylation impairs long-range ET, shortens the long-distance charge conduit between the partners, strengthens their interaction, and departs it from equilibrium. These results unveil a nanoscopic view of the interaction between redox protein partners in electron transport chains and its mechanisms of regulation.

Olfactory receptors (ORs) comprise the largest multigene family in the vertebrates. They belong to the class A (rhodopsin-like) family of G protein-coupled receptors (GPCRs), which are the most abundant membrane proteins, having widespread, significant roles in signal transduction in cells, and therefore, they are a major pharmacological target. Moreover, ORs displayed high selectivity and sensitivity towards odorant detection, a characteristic that raised the interest for developing biohybrid sensors based on ORs for the detection of volatile compounds. The transduction of odorant binding into cellular signaling by ORs is not well understood and knowing its mechanism would enable developing new pharmacology and high performance biohybrid electronic sensors. Recent findings suggest that ligand recognition by ORs is determined by the nanoscale alterations of charge distribution in the receptor structure (Ref). However, the electrical characterization of ORs and their response towards ligand binding in bulk experiments is subjected to microscopic models and assumptions [2]. Here, we have directly determined the nanoscale electrical properties of ORs with unprecedented control over the receptor orientation, and their change upon odorant binding, using electrochemical scanning tunneling microscopy (EC-STM) in near-physiological conditions. Recordings of current versus time, distance, and electrochemical potential allows determining the OR impedance parameters and their dependence with odorant binding. The simultaneous measurement of RC equivalent by means of the open-circuit voltage (VOC) allows increasing the electrical sensitivity at the single receptor level for biosensing applications. Our results allow validating OR structural-electrostatic models and their functional activation processes.

The transport of electrons along photosynthetic and respiratory chains involves a series of enzymatic reactions that are coupled through redox mediators, including proteins and small molecules. The use of native and synthetic redox probes is key to understanding charge transport mechanisms and to the design of bioelectronic sensors and solar energy conversion devices. However, redox probes have limited tunability to exchange charge at the desired electrochemical potentials (energy levels) and at different protein sites. Herein, we take advantage of electrochemical scanning tunneling microscopy (ECSTM) to control the Fermi level and nanometric position of the ECSTM probe in order to study electron transport in individual photosystem I (PSI) complexes. Current–distance measurements at different potentiostatic conditions indicate that PSI supports long-distance transport that is electrochemically gated near the redox potential of P700, with current extending farther under hole injection conditions.

The ability to control neural activity is essential for research not only in basic neuroscience, as spatiotemporal control of activity is a fundamental experimental tool, but also in clinical neurology for therapeutic brain interventions. Transcranial‐magnetic, ultrasound, and alternating/direct current (AC/DC) stimulation are some available means of spatiotemporal controlled neuromodulation. There is also light‐mediated control, such as optogenetics, which has revolutionized neuroscience research, yet its clinical translation is hampered by the need for gene manipulation. As a drug‐based light‐mediated control, the effect of a photoswitchable muscarinic agonist (Phthalimide‐Azo‐Iper (PAI)) on a brain network is evaluated in this study. First, the conditions to manipulate M2 muscarinic receptors with light in the experimental setup are determined. Next, physiological synchronous emergent cortical activity consisting of slow oscillations—as in slow wave sleep—is transformed into a higher frequency pattern in the cerebral cortex, both in vitro and in vivo, as a consequence of PAI activation with light. These results open the way to study cholinergic neuromodulation and to control spatiotemporal patterns of activity in different brain states, their transitions, and their links to cognition and behavior. The approach can be applied to different organisms and does not require genetic manipulation, which would make it translational to humans., Brain pathologies often require drug treatments, however drugs act all over the central nervous system. Wouldn't it be good to determine where/when a drug should be active? Drugs can be made sensitive to light, to be activated at specific times and locations. This study demonstrates that a light‐activated cholinergic drug can effectively modulate activity in the cerebral cortex network.

Photoinduced charge separation and transport through photosystem I (PSI) is an essential part of the photosynthetic electron transport chain. To investigate charge exchange processes mediated by the P700 reaction center of PSI, we have developed a strategy to functionalize gold electrodes with PSI complexes that orients and exposes their luminal side to the electrolyte. Bulk photoelectrochemical measurements demonstrate that PSI remains functional in a wide sample potential range around 0 mV/SSC. Electrochemical scanning tunneling microscopy (ECSTM) imaging of individual complexes shows lateral sizes in agreement with the dimensions of PSI and an apparent height that is gated by the probe potential of ECTSM as reported for smaller globular redox proteins. This experimental setup enables ECSTM current-distance spectroscopic measurements that unequivocally correspond to the P700 side of PSI. In these conditions, we observe that the spatial span of the current is enhanced (the distance-decay rate β is reduced) through the solution at sample potential 0 mV/SSC and probe potential 400 mV/SSC. This process corresponds to hole injection into an electronic state that is available in the absence of illumination. We propose that a pair of tryptophan residues located near P700 and known to integrate the hydrophobic recognition site for plastocyanin may have an additional role as hole exchange mediator involved in charge transport through PSI.

Photoinduced charge separation and transport through photosystem I (PSI) is an essential part of the photosynthetic electron transport chain. To investigate charge exchange processes mediated by the P700 reaction center of PSI, we have developed a strategy to functionalize gold electrodes with PSI complexes that orients and exposes their luminal side to the electrolyte. Bulk photoelectrochemical measurements demonstrate that PSI remains functional in a wide sample potential range around 0 mV/SSC. Electrochemical scanning tunneling microscopy (ECSTM) imaging of individual complexes shows lateral sizes in agreement with the dimensions of PSI and an apparent height that is gated by the probe potential of ECTSM as reported for smaller globular redox proteins. This experimental setup enables ECSTM current-distance spectroscopic measurements that unequivocally correspond to the P700 side of PSI. In these conditions, we observe that the spatial span of the current is enhanced (the distance-decay rate β is reduced) through the solution at sample potential 0 mV/SSC and probe potential 400 mV/SSC. This process corresponds to hole injection into an electronic state that is available in the absence of illumination. We propose that a pair of tryptophan residues located near P700 and known to integrate the hydrophobic recognition site for plastocyanin may have an additional role as hole exchange mediator involved in charge transport through PSI.

Clathrin-mediated endocytosis (CME) is an essential cellular process, which is evolutionarily conserved among eukaryotes. Yeast constitutes a powerful genetic model to dissect the complex endocytic machinery, yet there is a lack of pharmacological agents that could complement genetics in selectively and reversibly interfere with CME in these organisms. TL2 is a light-regulated peptide inhibitor that targets the AP2/β-arrestin interaction and that can photocontrol CME with high spatiotemporal precision in mammalian cells. Here, we study endocytic protein dynamics by live-cell imaging of the fluorescently tagged coat-associated protein Sla1-GFP and demonstrate that TL2 retains its inhibitory activity in S. cerevisiae spheroplasts, thus providing a unique tool for acute and reversible CME modulation in yeast.

Photosynthetic reactions in plants, algae, and cyanobacteria are driven by photosystem I and photosystem II complexes, which specifically reduce or oxidize partner redox biomolecules. Photosynthetic complexes can also bind synthetic organic molecules, which inhibit their photoactivity and can be used both to study the electron transport chain and as herbicides and algicides. Thus, their development, characterization, and sensing bears fundamental and applied interest. Substantial efforts have been devoted to developing photosensors based on photosystem II to detect compounds that bind to the plastoquinone sites of this complex. In comparison, photosystem I based sensors have received less attention and could be used to identify novel substances displaying phytotoxic effects, including those obtained from natural product extracts. We have developed a robust procedure to functionalize gold electrodes with photo- and redox-active photosystem I complexes based on transparent gold and a thiolate self-assembled monolayer, and we have obtained reproducible electrochemical photoresponses. Chronoamperometric recordings have allowed us to measure photocurrents in the presence of the viologen derivative paraquat at concentrations below 100 nM under lock-in operation and a sensor dynamic range spanning six orders of magnitude up to 100 mM. We have modeled their time course to identify the main electrochemical processes and limiting steps in the electron transport chain. Our results allow us to isolate the contributions from photosystem I and the redox mediator, and evaluate photocurrent features (spectral and power dependence, fast transient kinetics) that could be used as a sensing signal to detect other inhibitors and modulators of photosystem I activity.

Visual Abstract, Photopharmacology is a unique approach that through a combination of photochemistry methods and advanced life science techniques allows the study and control of specific biological processes, ranging from intracellular pathways to brain circuits. Recently, a first photochromic channel blocker of anion-selective GABAA receptors, the azobenzene-nitrazepam-based photochromic compound (Azo-NZ1), has been described. In the present study, using patch-clamp technique in heterologous system and in mice brain slices, site-directed mutagenesis and molecular modeling we provide evidence of the interaction of Azo-NZ1 with glycine receptors (GlyRs) and determine the molecular basis of this interaction. Glycinergic synaptic neurotransmission determines an important inhibitory drive in the vertebrate nervous system and plays a crucial role in the control of neuronal circuits in the spinal cord and brain stem. GlyRs are involved in locomotion, pain sensation, breathing, and auditory function, as well as in the development of such disorders as hyperekplexia, epilepsy, and autism. Here, we demonstrate that Azo-NZ1 blocks in a UV-dependent manner the activity of α2 GlyRs (GlyR2), while being barely active on α1 GlyRs (GlyR1). The site of Azo-NZ1 action is in the chloride-selective pore of GlyR at the 2’ position of transmembrane helix 2 and amino acids forming this site determine the difference in Azo-NZ1 blocking activity between GlyR2 and GlyR1. This subunit-specific modulation is also shown on motoneurons of brainstem slices from neonatal mice that switch during development from expressing “fetal” GlyR2 to “adult” GlyR1 receptors.

Manipulation of neuronal activity using two-photon excitation of azobenzene photoswitches with near-infrared light has been recently demonstrated, but their practical use in neuronal tissue to photostimulate individual neurons with three-dimensional precision has been hampered by firstly, the low efficacy and reliability of NIR-induced azobenzene photoisomerization compared to one-photon excitation, and secondly, the short cis state lifetime of the two-photon responsive azo switches. Here we report the rational design based on theoretical calculations and the synthesis of azobenzene photoswitches endowed with both high two-photon absorption cross section and slow thermal back-isomerization. These compounds provide optimized and sustained two-photon neuronal stimulation both in light-scattering brain tissue and in Caenorhabditis elegans nematodes, displaying photoresponse intensities that are comparable to those achieved under one-photon excitation. This finding opens the way to use both genetically targeted and pharmacologically selective azobenzene photoswitches to dissect intact neuronal circuits in three dimensions., Two-photon absorption capacity of azobenzene photoswitches usually comes with a reduction in thermal stability. Here, the authors developed photoswitches with high two-photon sensitivity and enhanced cis isomer thermal lifetime for the control of glutamate receptors.

International audience; Glycine receptors (GlyRs) are indispensable for maintaining excitatory/inhibitory balance in neuronal circuits that control reflexes and rhythmic motor behaviors. Here we have developed Glyght, a GlyR ligand controlled with light. It is selective over other Cys-loop receptors, is active in vivo, and displays an allosteric mechanism of action. The photomanipulation of glycinergic neurotransmission opens new avenues to understanding inhibitory circuits in intact animals and to developing drug-based phototherapies.

Optogenetic and photopharmacological tools to manipulate neuronal inhibition have limited efficacy and reversibility. We report the design, synthesis, and biological evaluation of Fulgazepam, a fulgimide derivative of benzodiazepine that behaves as a pure potentiator of ionotropic γ‐aminobutyric acid receptors (GABAARs) and displays full and reversible photoswitching in vitro and in vivo. The compound enables high‐resolution studies of GABAergic neurotransmission, and phototherapies based on localized, acute, and reversible neuroinhibition., Fulgazepam: Herein, the design, synthesis, and biological evaluation of Fulgazepam, a fulgimide derivative of benzodiazepine that behaves as a pure potentiator of ionotropic γ‐aminobutyric acid receptors (GABAARs) and displays full and reversible photoswitching in vitro and in vivo, is reported.

Summary Kainate receptors (KARs) mediate postsynaptic currents with a key impact on neuronal excitability. However, the molecular determinants controlling KAR postsynaptic localization and stabilization are poorly understood. Here, we exploit optogenetic and single-particle tracking approaches to study the role of KAR conformational states induced by glutamate binding on KAR lateral mobility at synapses. We report that following glutamate binding, KARs are readily and reversibly trapped at glutamatergic synapses through increased interaction with the β-catenin/N-cadherin complex. We demonstrate that such activation-dependent synaptic immobilization of KARs is crucial for the modulation of short-term plasticity of glutamatergic synapses. Thus, the present study unveils the crosstalk between conformational states and lateral mobility of KARs, a mechanism regulating glutamatergic signaling, particularly in conditions of sustained synaptic activity., Graphical Abstract, Highlights • Anchoring of KARs at glutamatergic synapses depends on receptor-glutamate binding • KARs activation/desensitization promotes receptors trapping at glutamatergic synapses • N-cadherins mediate the KAR activation/desensitization-dependent anchoring at synapses • Synaptic trapping of desensitized KARs affects short-term synaptic plasticity, Polenghi et al. report that following their activation, kainate receptors (KARs) are readily trapped at glutamatergic synapses in the open/desensitized state. This mechanism defines the number of ready-to-be-activated KARs at synapses, with direct impacts on short-term synaptic plasticity.

Altres ajuts: CERCA Programme/Generalitat de Catalunya Aquest article té una correcció a 10.1039/d0sc90189j The spatiotemporal control of cellular dynamic processes has great fundamental interest but lacks versatile molecular tools. Dynamin is a key protein in endocytosis and an appealing target to manipulate cell trafficking using patterns of light. We have developed the first photoswitchable small-molecule inhibitors of endocytosis (dynazos), by a stepwise design of the photochromic and pharmacological properties of dynasore, a dynamin inhibitor. We have characterized their photochromism with UV-visible and transient absorption spectroscopy and their biological activity using fluorescence microscopies and flow cytometry. Dynazos are water-soluble, cell permeable, and photostable, and enable fast, single-wavelength photoswitchable inhibition of clathrin-mediated endocytosis at micromolar concentration.

Correction for ‘Photoswitchable dynasore analogs to control endocytosis with light’ by Núria Camarero et al., Chem. Sci., 2020, 11, 8981–8988, DOI: 10.1039/d0sc03820b.

Chemical modification with nanometer precision can be used to probe and to improve the function of complex molecular entities, from organic materials to proteins and their assemblies. Using the pigment arrangement in photosynthetic light-harvesting as inspiration, we show that molecular photosensitizers can be located at well-defined distances from photoisomerizable units in proteins in order to enhance and spectrally shift their photoresponses. The approach is demonstrated in Channelrhodopsin-2 (ChR2) and in the light-gated ionotropic glutamate receptor (LiGluR), two archetypical actuators in optogenetics and photopharmacology that have been used both for fundamental and therapeutic purposes. These proof-of-concept experiments together with theoretical simulations predict that the photosensitivity can be increased several orders of magnitude using these means, thus providing a unique methodology to boost the performance of current optogenetic and photopharmacological toolboxes.

Charge separation and transport through the reaction center of photosystem I (PSI) is an essential part of the photosynthetic electron transport chain. A strategy is developed to immobilize and orient PSI complexes on gold electrodes allowing to probe the complex's electron acceptor side, the chlorophyll special pair P700. Electrochemical scanning tunneling microscopy (ECSTM) imaging and current-distance spectroscopy of single protein complex shows lateral size in agreement with its known dimensions, and a PSI apparent height that depends on the probe potential revealing a gating effect in protein conductance. In current-distance spectroscopy, it is observed that the distance-decay constant of the current between PSI and the ECSTM probe depends on the sample and probe electrode potentials. The longest charge exchange distance (lowest distance-decay constant ?) is observed at sample potential 0 mV/SSC (SSC: reference electrode silver/silver chloride) and probe potential 400 mV/SSC. These potentials correspond to hole injection into an electronic state that is available in the absence of illumination. It is proposed that a pair of tryptophan residues located at the interface between P700 and the solution and known to support the hydrophobic recognition of the PSI redox partner plastocyanin, may have an additional role as hole exchange mediator in charge transport through PSI.© 2021 Wiley-VCH GmbH.

The control of ligand-gated receptors with light using photochromic compounds has evolved from the first handcrafted examples to accurate, engineered receptors, whose development is supported by rational design, high-resolution protein structures, comparative pharmacology and molecular biology manipulations. Photoswitchable regulators have been designed and characterized for a large number of ligand-gated receptors in the mammalian nervous system, including nicotinic acetylcholine, glutamate and GABA receptors. They provide a well-equipped toolbox to investigate synaptic and neuronal circuits in all-optical experiments. This focused review discusses the design and properties of these photoswitches, their applications and shortcomings and future perspectives in the field. Linked articles This article is part of a themed section on Nicotinic Acetylcholine Receptors. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v175.11/issuetoc.

The γ-aminobutyric acid gated chloride channel represents the major mediator of inhibitory neurotransmission in the mammalian central nervous system and its dysfunction is related to severe diseases like epilepsy and depression, which can be relieved by the application of allosteric modulators. However, the drugs’ potential side-effects limit their application for long-term treatment. Applying light as external stimulus to modify the pharmacophore’s activity, as emerged in the field of photopharmacology, provides a non-invasive tool with high spatial and temporal resolution for the modulation of protein function. Herein, we report the design, synthesis, and biological evaluation of photochromic fulgimide-based benzodiazepine derivatives as light-controllable potentiators of GABAA receptors (GABAARs). A photocontrolled potentiator of GABAARs (Fulgazepam) has been identified that does not display agonist or antagonist activity and allows manipulating zebrafish larvae swimming.

Glycine receptors (GlyRs) are indispensable to maintain excitatory/inhibitory balance in neuronal circuits controlling reflex and rhythmic motor behaviors. Here we have developed Glyght, the first GlyR ligand controlled with light. It is selective over other cys-loop receptors, active in vivo, and displays an allosteric mechanism of action. The photomanipulation of glycinergic neurotransmission opens new avenues to understand inhibitory circuits in intact animals, and to develop drug-based phototherapies.

The physiological activity of proteins is often studied with loss-of-function genetic approaches, but the corresponding phenotypes develop slowly and can be confounding. Photopharmacology allows direct, fast, and reversible control of endogenous protein activity, with spatiotemporal resolution set by the illumination method. Here, we combine a photoswitchable allosteric modulator (alloswitch) and 2-photon excitation using pulsed near-infrared lasers to reversibly silence metabotropic glutamate 5 (mGlu5) receptor activity in intact brain tissue. Endogenous receptors can be photoactivated in neurons and astrocytes with pharmacological selectivity and with an axial resolution between 5 and 10 μm. Thus, 2-photon pharmacology using alloswitch allows investigating mGlu5-dependent processes in wild-type animals, including synaptic formation and plasticity, and signaling pathways from intracellular organelles. © 2019 National Academy of Sciences. All rights reserved., ACKNOWLEDGMENTS. We thank Jordi Hernando (Autonomous University of Barcelona) for useful discussions on 2-photon excitation; Pere Català (Utrecht University) for help with GCaMP; Francisco Ciruela (University of Barcelona) for mGlu5-eYFP plasmid; Erin Schuman and Stephan Junek (Max Planck Institute for Brain Research, Frankfurt) for preliminary 2-photon excitation experiments; and Ashraf Muhaisen (University of Barcelona) for help with slicing. This research received funding from European Union Research and Innovation Programme Horizon 2020 [Human Brain Project SGA2 Grant Agreement 785907 (WaveScalES)], European Research ERA-Net SynBio programme (Modulightor project), and financial support from Agency for Management of University and Research Grants/Generalitat de Catalunya (CERCA Programme; 2017-SGR-1442 project), Fonds Européen de Développement Économique et Régional (FEDER) funds, Ministry of Economy and Competitiveness (MINECO)/FEDER (Grant CTQ2016-80066-R), and the Fundaluce foundation. S.P. was supported by an FI fellowship from the Agency for Management of University and Research Grants/Generalitat de Catalunya (2014FI_B2 00160). H.L. was supported by an Institute for Bioengineering of Catalonia Severo Ochoa International PhD Programme fellowship from MINECO. M.B. was supported by a H2020-MSCA-IF Reintegration Grant. K.E.P. receives support from NIH/National Institute of Neurological Disorders and Stroke Grant R01NS099254 and NSF Biophotonics Grant 1604544. E.S. receives support from MINECO (Grant SAF2016-7426).

The transport of electrons along photosynthetic and respiratory chains involves a series of enzymatic reactions that are coupled through redox mediators, including proteins and small molecules. The use of native and synthetic redox probes is key to understand charge transport mechanisms, and to design bioelectronic sensors and solar energy conversion devices. However, redox probes have limited tunability to exchange charge at the desired electrochemical potentials (energy levels) and at different protein sites. Here, we take advantage of electrochemical scanning tunneling microscopy (ECSTM) to control the Fermi energy and nanometric position of the ECSTM probe in order to study electron transport in individual photosystem I (PSI) complexes. Current-distance measurements at different potentiostatic conditions indicate that PSI supports long-distance transport that is electrochemically gated near the redox potential of P700, with current extending farther under hole injection conditions.

Remote control of physiological functions with light offers the promise of unveiling their complex spatiotemporal dynamics in vivo, and enabling highly focalized therapeutic interventions with reduced systemic toxicity. Optogenetic methods have been implemented in the heart, but the need of genetic manipulation jeopardizes clinical applicability. This study aims at developing, testing and validating the first light-regulated drug with cardiac effects, in order to avoid the requirement of genetic manipulation offered by optogenetic methods. A M2 muscarinic acetylcholine receptors (mAChRs) light-regulated drug (PAI) was designed, synthesized and pharmacologically characterized. The design was based on the orthosteric mAChRs agonist Iperoxo, an allosteric M2 ligand, and a photoswitchable azobenzene linker. PAI can be reversibly photoisomerized between cis and trans configurations under ultraviolet (UV) and visible light, respectively, and it reversibly photoswitches the activity of M2 muscarinic acetylcholine receptors. We have evaluated in vitro photoresponses using a calcium imaging assay in genetically unmodified receptors overexpressed in mammalian cells. Furthermore, using this new chemical tool, we demonstrate for the first time photoregulation of cardiac function in vivo in wildtype frog tadpoles and in rats with a method that does not require genetic manipulation. Such a new approach may enable enhanced spatial and temporal selectivity for cardiovascular drugs.

OptoGluNAM4.1, a negative allosteric modulator (NAM) of metabotropic glutamate receptor 4 (mGlu4) contains a reactive group that covalently binds to the receptor and a blue-light-activated, fast-relaxing azobenzene group that allows reversible receptor activity photocontrol in vitro and in vivo. OptoGluNAM4.1 induces light-dependent behavior in zebrafish and reverses the activity of the mGlu4 agonist LSP4-2022 in a mice model of chronic pain, defining a photopharmacological tool to better elucidate the physiological roles of the mGlu4 receptor in the nervous system. © 2016 Elsevier Ltd, We are grateful to C. Serra, L. Muñoz, J. Hernando, F. Malhaire, Y. Pérez, M. Izquierdo-Serra, F. Aguado, S. Laffray, E. Bourinet, F.Codony (GenIUL), and Y. Chomis (Viewpoint) for helpful discussions and technical support. A.F. is supported by a Fondation Lefoulon Delalande postdoctoral fellowship , C.J. by a grant from INSERM ATIP-AVENIR and Marie Curie CIG ( PCIG12-GA-2012-332772 ). A.F. and C.J. are members of the Laboratory of Excellence Ion Channel Science and Therapeutics supported by a grant from the ANR . J.-P.P. is a member of the Laboratory of Excellence Epingenmed. We acknowledge financial support from the European Union's Seventh Framework Program for research, technological development, and demonstration under grant agreements 270483 (Focus), 210355 (Opticalbullet), and 335011 (Theralight) to P.G.; the Federation of European Biochemical Societies ; the Catalan government ( 2012FI_B 01122 to S.P., 2014SGR-1251 to P.G., and 2014SGR-0109 to A. Llebaria); the Spanish Government ( SAF2014-58396-R to J.G., CTQ2014-57020-R to A.L., and CTQ2013-43892R to P.G.); the ERANET Neuron LIGHTPAIN project (to A.L., J.G., and J.-P.P.); the Ramón Areces Foundation , the ERANET SynBio Modulightor project (to P.G.); the HBP Wavescales project (to P.G.); the Fondation Recherche Médicale (FRM team DEQ20130326522 to J.P.P.); the Agence Nationale de la Recherche ( ANR-13-BSV1-006 to C.G.) and the Beatriu de Pinós program of Agència de Gestió d'Ajuts Universitaris i de Recerca (AGAUR) for the support of X.R.

The efficacy and tolerability of systemically administered anticancer agents are limited by their off-target effects. Precise spatiotemporal control over their cytotoxic activity would allow improving chemotherapy treatments, and light-regulated drugs are well suited to this purpose. We have developed phototrexate, the first photoswitchable inhibitor of the human dihydrofolate reductase (DHFR), as a photochromic analogue of methotrexate, a widely prescribed chemotherapeutic drug to treat cancer and psoriasis. Quantification of the light-regulated DHFR enzymatic activity, cell proliferation, and in vivo effects in zebrafish show that phototrexate behaves as a potent antifolate in its photoactivated cis configuration and that it is nearly inactive in its dark-relaxed trans form. Thus, phototrexate constitutes a proof-of-concept to design light-regulated cytotoxic small molecules and a step forward to develop targeted anticancer photochemotherapies with localized efficacy and reduced adverse effects.

Cellular adhesion and differentiation is conditioned by the nanoscale disposition of the extracellular matrix (ECM) components, with local concentrations having a major effect. Here we present a method to obtain large-scale uneven nanopatterns of arginine-glycine-aspartic acid (RGD)-functionalized dendrimers that permit the nanoscale control of local RGD surface density. Nanopatterns are formed by surface adsorption of dendrimers from solutions at different initial concentrations and are characterized by water contact angle (CA), X-ray photoelectron spectroscopy (XPS), and scanning probe microscopy techniques such as scanning tunneling microscopy (STM) and atomic force microscopy (AFM). The local surface density of RGD is measured using AFM images by means of probability contour maps of minimum interparticle distances and then correlated with cell adhesion response and differentiation. The nanopatterning method presented here is a simple procedure that can be scaled up in a straightforward manner to large surface areas. It is thus fully compatible with cell culture protocols and can be applied to other ligands that exert concentration-dependent effects on cells.

Despite the importance of electron transfer (ET) between redox proteins in photosynthesis and respiration, the inter-protein ET rate between redox partner proteins has never been measured as a function of their separation in aqueous solution. Here we use electrochemical tunneling spectroscopy to show that the current between two protein partners decays along more than 10 nm in the solution. Molecular dynamics simulations reveal a reduced ionic density and extended electric field in the volume confined between the proteins. The distance-decay factor and the calculated local barrier for ET are regulated by the electrochemical potential applied to the proteins. Redox partners could use electrochemically gated, long distance ET through the solution in order to conciliate high ET specificity with weak binding, thus keeping high turnover rates in the crowded environment of cells., The project was funded by CERCA, FEDER, and Networking Biomedical Research Center (CIBER), Spain. CIBER is an initiative funded by the VI National R&D&i Plan 2008–2011, Iniciativa Ingenio 2010, Consolider Program, CIBER Actions, and the Instituto de Salud Carlos III, with the support of the European Regional Development Fund. This work was financially supported by the Commission for Universities and Research of the Department of Innovation, Universities, and Enterprise of the Generalitat de Catalunya (2017 SGR 1442, 2014 SGR 1442, and 2017 SGR 1189), by the Andalusian Government (BIO198), and the projects CTQ2016–80066-R, CTQ2015-66194-R, CTQ2017-85496-P and Spanish Structures of Excellence Maria de Maeztu, MDM2017-0767, and BFU2015-71017-P/BMC awarded by the Spanish Ministry of Economy and Competitiveness. A.N.-H. thanks the Generalitat de Catalunya-AGAUR for a FI scholarship. MINECO/ICTI2013-2016/CTQ2015-66194-R MINECO/ICTI2013-2016/BFU2015-71017-P MICIU/ICTI2017-2020/CTQ2017-85496-P MICIU/ICTI2017-2020/MDM2017-0767

Bioelectronics moves toward designing nanoscale electronic platforms that allow in vivo determinations. Such devices require interfacing complex biomolecular moieties as the sensing units to an electronic platform for signal transduction. Inevitably, a systematic design goes through a bottom-up understanding of the structurally related electrical signatures of the biomolecular circuit, which will ultimately lead us to tailor its electrical properties. Toward this aim, we show here the first example of bioengineered charge transport in a single-protein electrical contact. The results reveal that a single point-site mutation at the docking hydrophobic patch of a Cu-azurin causes minor structural distortion of the protein blue Cu site and a dramatic change in the charge transport regime of the single-protein contact, which goes from the classical Cu-mediated two-step transport in this system to a direct coherent tunneling. Our extensive spectroscopic studies and molecular-dynamics simulations show that the proteins' folding structures are preserved in the single-protein junction. The DFT-computed frontier orbital of the relevant protein segments suggests that the Cu center participation in each protein variant accounts for the different observed charge transport behavior. This work is a direct evidence of charge transport control in a protein backbone through external mutagenesis and a unique nanoscale platform to study structurally related biological electron transfer.

Phenylazopyridines are photoisomerizable compounds with high potential to control biological functions with light. We have obtained a series of phenylazopyridines with light dependent activity as negative allosteric modulators (NAM) of metabotropic glutamate receptor subtype 5 (mGlu5). Here we describe the factors needed to achieve an operational molecular photoisomerization and its effective translation into in vitro and in vivo receptor photoswitching, which includes zebrafish larva motility and the regulation of the antinociceptive effects in mice. The combination of light and some specific phenylazopyridine ligands displays atypical pharmacological profiles, including light-dependent receptor overactivation, which can be observed both in vitro and in vivo. Remarkably, the localized administration of light and a photoswitchable compound in the peripheral tissues of rodents or in the brain amygdalae results in an illumination-dependent analgesic effect. The results reveal a robust translation of the phenylazopyridine photoisomerization to a precise photoregulation of biological activity. © 2016 American Chemical Society., We are grateful to C. Serra and L. Muñoz for synthetic and analytical support, F. Malhaire for technical support in cell-based pharmacological assays, and Y. Pérez for NMR support. This research has been supported by RecerCaixa foundation (2010ACUP00378 to P.G., J.G., and A.L.), the Marató de TV3 Foundation (110230 to J.G., 110231 to A.L., 110232 to C.G., and 111531 to P.G.), the Catalan government (2010 BP-A 00194 to X.R., 2012FI_B 01122 to S.P., 2012 CTP 00033 and 2012 BE1 00597 to X.G.-S., 2014SGR-1251 to P.G., and 2014SGR-00109 to A.L.), the Spanish Government (CTQ2014-57020-R and PCIN-2013-017-C03-01 to A.L., PIE14/00034, SAF2014-55700-P, and PCIN-2013-019-C03-03 to F.C., and SAF2014-58396-R to J.G.), AWT (SBO-140028) to F.C., and the ERANET Neuron LIGHTPAIN project (to A.L., F.C., J.G., and J.-P.P.); SynBio MODULIGHTOR, Human Brain Project WAVESCALES and Ramon Areces foundation grants (to P.G.); the Agence Nationale de la Recherche (ANR-16-CE16-0010 to A.L. and C.G.).

Understanding how charges move through and between biomolecules is a fundamental question that constitutes the basis for many biological processes. On the other hand, it has potential applications in the design of sensors based on biomolecules and single molecule devices. In this review we introduce the study of the electron transfer (ET) process in biomolecules, providing an overview of the fundamental theory behind it and the different experimental approaches. The ET in proteins is introduced by reviewing a complete electronic characterization of a redox protein (azurin) using electrochemical scanning tunnelling microscopy (ECSTM). The ET process in DNA is overviewed and results from different experimental approaches are discussed. Finally, future directions in the study of the ET process in biomolecules are introduced as well as examples of possible technological applications.

Compounds that modulate the function of G-protein-coupled receptors (GPCRs) by binding to their allosteric sites are of potential interest for the treatment of multiple CNS and non-CNS disorders. Allosteric ligands can act either as positive (PAM), negative (NAM), or silent (SAM) receptor modulators and have numerous advantages over classic orthosteric compounds, including improved GPCR-subtype selectivity; the capacity to adapt to physiological conditions; and better safety profiles. Despite these benefits, allosteric modulators are difficult to design and optimize and are often prone to “molecular switching”: a structural phenomenon by which very subtle chemical variations in the ligand result in unexpected changes in selectivity profiles or pharmacology, changing PAMs to NAMs or vice versa. Here, we report the discovery of a nanomolar and subtype selective NAM of metabotropic glutamate receptor 5 (mGlu5) through a targeted “double effect molecular switch” of a potent mGlu4 PAM, and suggests a promising approach towards the discovery of novel mGluR allosteric modulators.

and single-molecule char-acteristics. Finding out whether such switching events can also be observed in redox proteins, and what their contribu-tion to the average electrochemical behavior is, could help to understand the mechanisms behind biological ET processes, as well as lead to the designing of reliable devices based on individual or small assemblies of molecules. In single-azurin studies, deviations from the average redox behavior have been observed in current–time traces of ‘wired’ junctions by ECSTM.

A lipase was immobilized on transparent agarose microspheres and genetically engineered to specifically anchor photochromic molecules into its catalytic site. Several combinations of azobenzene and spiropyran groups were conjugated to cysteines introduced at different positions near the active center. Light modulated the catalytic properties of the resulting solid bioconjugates, and such modulation depended on both the nature of the photochromic compound and the anchoring position. Covalent anchoring of azobenzene derivatives to the residue 295 of the lipase 2 from Bacillus thermocathenolatus triggered lipase preference for the S isomer under UV light, whereas visible light promoted preference for the R isomer. Molecular dynamics simulations indicate that conjugating photochromic compounds into the catalytic cavity allows manipulating the steric hindrance and binding energy of the substrates, leading to an enantioselective molecular fit in certain cases. Using this approach, we report for the first time the control of enzyme properties using light in the solid phase., We are grateful for financial support from the Human Frontier Science Program through a Career Development Award (CDA022/2006), from the European Research Council through the “Opticalbullet” Starting Grant (ERC-StG210355/2007), from the European Commission through the “Focus” ICT-FET Grant (FP7-ICT-2009-270483), from the Ministry of Education through Grants CTQ2008-06160 and CTQ2011-25871, a “Juan de la Cierva” research associate fellowship, and FPI and FPU fellowships, and from the RecerCaixa and Marató de TV3 foundations.

Cell adhesion processes are governed by the nanoscale arrangement of the extracellular matrix (ECM), being more affected by local rather than global concentrations of cell adhesive ligands. In many cell-based studies, grafting of dendrimers on surfaces has shown the benefits of the local increase in concentration provided by the dendritic configuration, although the lack of any reported surface characterization has limited any direct correlation between dendrimer disposition and cell response. In order to establish a proper correlation, some control over dendrimer surface deposition is desirable. Here, dendrimer nanopatterning has been employed to address arginine-glycine-aspartic acid (RGD) density effects on cell adhesion. Nanopatterned surfaces were fully characterized by atomic force microscopy (AFM), scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS), showing that tunable distributions of cell adhesive ligands on the surface are obtained as a function of the initial dendrimer bulk concentration. Cell experiments showed a clear correlation with dendrimer surface layout: Substrates presenting regions of high local ligand density resulted in a higher percentage of adhered cells and a higher degree of maturation of focal adhesions (FAs). Therefore, dendrimer nanopatterning is presented as a suitable and controlled approach to address the effect of local ligand density on cell response. Moreover, due to the easy modification of dendrimer peripheral groups, dendrimer nanopatterning can be further extended to other ECM ligands having density effects on cells. Open image in new window

Control of membrane traffic: Photoswitchable inhibitors of protein-protein interactions were applied to photoregulate clathrin-mediated endocytosis (CME) in living cells. Traffic light (TL) peptides acting as "stop" and "go" signals for membrane traffic can be used to dissect the role of CME in receptor internalization and in cell growth, division, and differentiation.

Understanding how molecular conductance depends on voltage is essential for characterizing molecular electronics devices. We reproducibly measured current-voltage characteristics of individual redox-active proteins by scanning tunneling microscopy under potentiostatic control in both tunneling and wired configurations. From these results, transition voltage spectroscopy (TVS) data for individual redox molecules can be calculated and analyzed statistically, adding a new dimension to conductance measurements. The transition voltage (TV) is discussed in terms of the two-step electron transfer (ET) mechanism. Azurin displays the lowest TV measured to date (0.4 V), consistent with the previously reported distance decay factor. This low TV may be advantageous for fabricating and operating molecular electronic devices for different applications. Our measurements show that TVS is a helpful tool for single-molecule ET measurements and suggest a mechanism for gating of ET between partner redox proteins.