Photoactive Protein Research Articles

Directional cerebrospinal fluid movement between brain ventricles in larval zebrafish.

BackgroundCerebrospinal fluid (CSF) contained within the brain ventricles contacts neuroepithelial progenitor cells during brain development. Dynamic properties of CSF movement may limit locally produced factors to specific regions of the developing brain. However, there is no study of in vivo CSF dynamics between ventricles in the embryonic brain. We address CSF movement using the zebrafish larva, during the major period of developmental neurogenesis.MethodsCSF movement was monitored at two stages of zebrafish development: early larva [pharyngula stage; 27–30 h post-fertilization (hpf)] and late larva (hatching period; 51–54 hpf) using photoactivatable Kaede protein to calculate average maximum CSF velocity between ventricles. Potential roles for heartbeat in early CSF movement were investigated using tnnt2a mutant fish (tnnt2a−/−) and chemical [2,3 butanedione monoxime (BDM)] treatment. Cilia motility was monitored at these stages using the Tg(βact:Arl13b–GFP) transgenic fish line.ResultsIn wild-type early larva there is net CSF movement from the telencephalon to the combined diencephalic/mesencephalic superventricle. This movement directionality reverses at late larval stage. CSF moves directionally from diencephalic to rhombencephalic ventricles at both stages examined, with minimal movement from rhombencephalon to diencephalon. Directional movement is partially dependent on heartbeat, as indicated in assays of tnnt2a−/− fish and after BDM treatment. Brain cilia are immotile at the early larval stage.ConclusionThese data demonstrate directional movement of the embryonic CSF in the zebrafish model during the major period of developmental neurogenesis. A key conclusion is that CSF moves preferentially from the diencephalic into the rhombencephalic ventricle. In addition, the direction of CSF movement between telencephalic and diencephalic ventricles reverses between the early and late larval stages. CSF movement is partially dependent on heartbeat. At early larval stage, the absence of motile cilia indicates that cilia likely do not direct CSF movement. These data suggest that CSF components may be compartmentalized and could contribute to specialization of the early brain. In addition, CSF movement may also provide directional mechanical signaling.Electronic supplementary materialThe online version of this article (doi:10.1186/s12987-016-0036-z) contains supplementary material, which is available to authorized users.

Photoactivatable protein labeling by singlet oxygen mediated reactions

Protein–protein interactions regulate many biological processes. Identification of interacting proteins is thus an important step toward molecular understanding of cell signaling. The aim of this study was to investigate the use of photo-generated singlet oxygen and a small molecule for proximity labeling of interacting proteins in cellular environment. The protein of interest (POI) was fused with a small singlet oxygen photosensitizer (miniSOG), which generates singlet oxygen (1O2) upon irradiation. The locally generated singlet oxygen then activated a biotin-conjugated thiol molecule to form a covalent bond with the proteins nearby. The labeled proteins can then be separated and subsequently identified by mass spectrometry. To demonstrate the applicability of this labeling technology, we fused the miniSOG to Skp2, an F-box protein of the SCF ubiquitin ligase, and expressed the fusion protein in mammalian cells and identified that the surface cysteine of its interacting partner Skp1 was labeled by the biotin–thiol molecule. This photoactivatable protein labeling method may find important applications including identification of weak and transient protein–protein interactions in the native cellular context, as well as spatial and temporal control of protein labeling.

Functional and Photochemical Characterization of a Light-Driven Proton Pump from the Gammaproteobacterium Pantoea vagans.

Photoactive retinal proteins are widely distributed throughout the domains of the microbial world (i.e., bacteria, archaea, and eukarya). Here we describe three retinal proteins belonging to a phylogenetic clade with a unique DTG motif. Light-induced decrease in the environmental pH and its inhibition by carbonyl cyanide m-chlorophenylhydrazone revealed that these retinal proteins function as light-driven outward electrogenic proton pumps. We further characterized one of these proteins, Pantoea vagans rhodopsin (PvR), spectroscopically. Visible spectroscopy and high-performance liquid chromatography revealed that PvR has an absorption maximum at 538 nm with the retinal chromophore predominantly in the all-trans form (>90%) under both dark and light conditions. We estimated the pKa values of the protonated Schiff base of the retinal chromophore and its counterion as approximately 13.5 and 2.1, respectively, by using pH titration experiments, and the photochemical reaction cycle of PvR was measured by time-resolved flash-photolysis in the millisecond timeframe. We observed a blue-shifted and a red-shifted intermediate, which we assigned as M-like and O-like intermediates, respectively. Decay of the M-like intermediate was highly sensitive to environmental pH, suggesting that proton uptake is coupled to decay of the M-like intermediate. From these results, we propose a putative model for the photoreaction of PvR.

Structural and Functional Studies on Photoactive Retinal Proteins: Light Becomes Drugs with Proteins

Retinal proteins possess vitamin A aldehyde (retinal) as a chromophore within seven transmembrane α-helices. Visible light absorption of them triggers trans-cis photoisomerization of the retinal chromophore and induces structural changes in the protein moiety, resulting in a variety of biological functions such as vision, ion transportation, and photosensing. Environmental genomics revealed that retinal proteins are widely distributed through all three biological kingdoms, eukarya, bacteria, and archaea, indicating the biological significance of their light energy conversion. In addition to their biological aspect, retinal proteins have become a focus of interest in part because of applications for optogenetics. On the basis of our results and other findings, we highlight the recent progress in structural and functional studies on retinal proteins.

Total chemical synthesis of photoactivatable proteins for light-controlled manipulation of antigen-antibody interactions.

We report the chemical synthesis of the first photo-activatable protein antigen that can be used to study antigen-antibody interaction mediated responses in B cells. This strategy facilitated fine tuning of the caged protein antigen to optimize its bioactivity and photochemical properties. One optimal molecule, HEL-K96NPE, was totally inert to hen egg lysozyme (HEL)-specific B cells and could only restore its antigenicity upon photoactivation. Combined with real time live cell imaging, the utility of HEL-K96NPE was demonstrated as a proof of concept to quantify B cell synapse formation and calcium influx responses at the single cell level.

Engineering of supramolecular photoactive protein architectures: the defined co-assembly of photosystem I and cytochrome c using a nanoscaled DNA-matrix.

The engineering of renewable and sustainable protein-based light-to-energy converting systems is an emerging field of research. Here, we report on the development of supramolecular light-harvesting electrodes, consisting of the redox protein cytochrome c working as a molecular scaffold as well as a conductive wiring network and photosystem I as a photo-functional matrix element. Both proteins form complexes in solution, which in turn can be adsorbed on thiol-modified gold electrodes through a self-assembly mechanism. To overcome the limited stability of self-grown assemblies, DNA, a natural polyelectrolyte, is used as a further building block for the construction of a photo-active 3D architecture. DNA acts as a structural matrix element holding larger protein amounts and thus remarkably improving the maximum photocurrent and electrode stability. On investigating the photophysical properties, this system demonstrates that effective electron pathways have been created.

Microbial rhodopsins of Halorubrum species isolated from Ejinoor salt lake in Inner Mongolia of China.

Microbial rhodopsins are photoactive proteins that use a retinal molecule as the photoactive center. Because of structural simplicity and functional diversity, microbial rhodopsins have been an excellent model system for structural biology. In this study, a halophilic archaea that has three microbial rhodopsin-type genes in its genome was isolated from Ejinoor salt lake in Inner Mongolia of China. A sequence of 16S rRNA showed that the strain belongs to Halorubrum genus and named Halorubrum sp. ejinoor (He). The translated amino acid sequences of its microbial rhodopsin-type genes suggest that they are homologs of archaerhodopsin (HeAR), halorhodopsin (HeHR) and sensory rhodopsin II (HeSRII). The mRNAs of three types of genes were detected by RT-PCR and their amounts were investigated by Real-Time RT-PCR. The amount of mRNA of HeSRII was the smallest and the amounts of of HeAR and HeHR were 30 times and 10 times greater than that of HeSRII. The results of light-induced pH changes suggested the presence of a light-driven proton pump and a light-driven chloride ion pump in the membrane vesicles of He. Flash induced absorbance changes of the He membrane fraction indicated that HeAR and HeHR are photoactive and undergo their own photocycles. This study revealed that three microbial rhodopsin-type genes are all expressed in the strain and at least two of them, HeAR and HeHR, are photochemically and physiologically active like BR and HR of Halobacterium salinarum, respectively. To our knowledge, this is the first report of physiological activity of HR-homolog of Halorubrum species.

Ion-pumping microbial rhodopsins.

Rhodopsins are light-sensing proteins used in optogenetics. The word “rhodopsin” originates from the Greek words “rhodo” and “opsis,” indicating rose and sight, respectively. Although the classical meaning of rhodopsin is the red-colored pigment in our eyes, the modern meaning of rhodopsin encompasses photoactive proteins containing a retinal chromophore in animals and microbes. Animal and microbial rhodopsins possess 11-cis and all-trans retinal, respectively, to capture light in seven transmembrane α-helices, and photoisomerizations into all-trans and 13-cis forms, respectively, initiate each function. Ion-transporting proteins can be found in microbial rhodopsins, such as light-gated channels and light-driven pumps, which are the main tools in optogenetics. Light-driven pumps, such as archaeal H+ pump bacteriorhodopsin (BR) and Cl− pump halorhodopsin (HR), were discovered in the 1970s, and their mechanism has been extensively studied. On the other hand, different kinds of H+ and Cl− pumps have been found in marine bacteria, such as proteorhodopsin (PR) and Fulvimarina pelagi rhodopsin (FR), respectively. In addition, a light-driven Na+ pump was found, Krokinobacter eikastus rhodopsin 2 (KR2). These light-driven ion-pumping microbial rhodopsins are classified as DTD, TSA, DTE, NTQ, and NDQ rhodopsins for BR, HR, PR, FR, and KR2, respectively. Recent understanding of ion-pumping microbial rhodopsins is reviewed in this paper.

Monitoring GM-CSF receptor/JAK2 activation in real time by live cell super-resolution fluorescence imaging

We proposed a GM-CSF receptor activation model wherein endocytotic clathrin-coated pits serve as a signaling platform for GM-CSF receptor and JAK2 activation after liganded-receptor-induced conformational change. To obtain evidence for this model, we used total internal reflection fluorescence microscopy (TIRFM) to analyze the behavior of JAK2, GMRβ and clathrin-coated pit at the plasma membrane in live cell. We found that the duration time of clathrin-coated pit has similar pattern to GMRβ and JAK2, but the tracking length and speed for clathrin-coated pit is shorter. Similar behavior patterns between JAK2 and GMRβ in this tracking analysis also consist with our model, which suggested that JAK2 and GMRβ coexist in plasma membrane. We also used the complementary metal oxide semiconductor (CMOS) camera to achieve the frame rate of 556 frames per second with the pixel number of 256 x 256 and high sensitivity, and used a switchable and photoactivatable fluorescence protein, dronpa, (in PALM) and photoswitchable labeling dye (in STORM) to reduce the acquisition time with the larger numbers of photon. At end, the behavior of clathrin-coated pit, GMRα, GMRβ and JAK2 at the plasma membrane in live cell was recorded and studied with temporal resolution of 2.5 second and spatial resolution of 30-40 nm. Besides, we would like to establish the live cell-Forster resonance energy transfer (FRET) and technology to visualize and analyze JAK2 activation by cytokines and the interaction of GM-CSF receptor with endocytotic machinery components. For this goal, we generated variant JAK2 biosensors, CFP-YFP and Clover-mRuby2, but these two generation biosensors were auto-activated without cytokine. To solve this problem, we inserted different length linker between JAK2 and fluorescent protein, and it seems work to reduce JAK2 autoactivation. Therefore, we will use this biosensor to study JAK2 activation and JAK2-GMRβ interaction.

An Engineered Split Intein for Photoactivated Protein Trans-Splicing.

Protein splicing is mediated by inteins that auto-catalytically join two separated protein fragments with a peptide bond. Here we engineered a genetically encoded synthetic photoactivatable intein (named LOVInC), by using the light-sensitive LOV2 domain from Avena sativa as a switch to modulate the splicing activity of the split DnaE intein from Nostoc punctiforme. Periodic blue light illumination of LOVInC induced protein splicing activity in mammalian cells. To demonstrate the broad applicability of LOVInC, synthetic protein systems were engineered for the light-induced reassembly of several target proteins such as fluorescent protein markers, a dominant positive mutant of RhoA, caspase-7, and the genetically encoded Ca2+ indicator GCaMP2. Spatial precision of LOVInC was demonstrated by targeting activity to specific mammalian cells. Thus, LOVInC can serve as a general platform for engineering light-based control for modulating the activity of many different proteins.

Structure-based engineering of Methionyl tRNA Synthetase for expression of photoactivatable proteins with photomethionine inE. coli.

Structure-based engineering of Methionyl tRNA Synthetase for expression of photoactivatable proteins with photomethionine in<i>E. coli</i>.

A photoactivatable green-fluorescent protein from the phylum Ctenophora.

You have accessMoreSectionsView PDF ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InRedditEmail Cite this article Haddock Steven H. D., Mastroianni Nadia and Christianson Lynne M. 2015A photoactivatable green-fluorescent protein from the phylum CtenophoraProc. R. Soc. B.2822015105520151055http://doi.org/10.1098/rspb.2015.1055SectionYou have accessRetractionA photoactivatable green-fluorescent protein from the phylum Ctenophora Steven H. D. Haddock Steven H. D. Haddock Google Scholar Find this author on PubMed Search for more papers by this author , Nadia Mastroianni Nadia Mastroianni Google Scholar Find this author on PubMed Search for more papers by this author and Lynne M. Christianson Lynne M. Christianson Google Scholar Find this author on PubMed Search for more papers by this author Steven H. D. Haddock Steven H. D. Haddock Google Scholar Find this author on PubMed Search for more papers by this author , Nadia Mastroianni Nadia Mastroianni Google Scholar Find this author on PubMed Search for more papers by this author and Lynne M. Christianson Lynne M. Christianson Google Scholar Find this author on PubMed Search for more papers by this author Published:07 August 2015https://doi.org/10.1098/rspb.2015.1055This article retracts the followingResearch ArticleA photoactivatable green-fluorescent protein from the phylum Ctenophorahttps://doi.org/10.1098/rspb.2009.1774 Steven H. D. Haddock, Nadia Mastroianni and Lynne M. Christianson volume 277issue 1685Proceedings of the Royal Society B: Biological Sciences16 December 2009In the years following the publication of ‘A photoactivatable green-fluorescent protein from the phylum Ctenophora’ [1], another research group [2] sequenced hydrozoan (Cnidaria) fluorescent proteins that were very similar to those we cloned from cDNA prepared from ctenophore specimens. We therefore now believe that the green-fluorescent proteins reported in our study are not from ctenophores, and were due to incorporation of cnidarian prey into the ctenophore tissues.Although our genes were cloned from two independent samples of mRNA taken years apart, the similarity of our sequences to those obtained from a siphonophore (Cnidaria, Hydrozoa) indicate that this mRNA was carried over from ingested material. This ctenophore species is known to prey on cnidarians, but we did not expect that mRNA would persist for as long as it did, and we regret our erroneous conclusion.What is remarkable about this situation is that the ctenophore, in addition to maintaining full-length mRNA for the fluorescent protein, also incorporated the proteins into its tissue to the extent that its bioluminescence emission was green-shifted. While the exact species of origin for these proteins is unknown, the photoactivatable properties of this fluorescent protein are as originally described, and it remains an interesting target for future research and application.Steven H. D. HaddockMonterey Bay Aquarium Research Institute, 7700 Sandholdt Road,Moss Landing, CA 95039, USAe-mail: [email protected]Nadia MastroianniAxxam SpA, San Raffaele, Biomedical Science Park, via Olgettina 58,20132 Milan, Italye-mail: [email protected]Lynne M. ChristiansonMonterey Bay Aquarium Research Institute, 7700 Sandholdt Road,Moss Landing, CA 95039, USAe-mail: [email protected]Footnotes© 2015 The Author(s)Published by the Royal Society. All rights reserved.References1Haddock SHD, Mastroianni N, Christianson LM. 2010A photoactivatable green-fluorescent protein from the phylum Ctenophora. Proc. R. Soc. B 277, 1155–1160. (doi:10.1098/rspb.2009.1774) Link, ISI, Google Scholar2Hunt ME, Modi CK, Aglyamova GV, Ravikant DVS, Meyer E, Matz MV. 2015Multi-domain GFP-like proteins from two species of marine hydrozoans. Photochem. Photobiol. Soc. 11, 637–644. (doi:10.1039/c1pp05238a) Crossref, ISI, Google Scholar Previous Article VIEW FULL TEXT DOWNLOAD PDF FiguresRelatedReferencesDetailsRelated articlesA photoactivatable green-fluorescent protein from the phylum Ctenophora16 December 2009Proceedings of the Royal Society B: Biological Sciences This Issue07 August 2015Volume 282Issue 1812 Article InformationDOI:https://doi.org/10.1098/rspb.2015.1055PubMed:26224709Published by:Royal SocietyOnline ISSN:1471-2954History: Published online07/08/2015Published in print07/08/2015 License:© 2015 The Author(s)Published by the Royal Society. All rights reserved. Citations and impact Subjectsbiochemistry Large datasets are available through Proceedings B's partnership with Dryad

The Signaling State of Orange Carotenoid Protein

Orange carotenoid protein (OCP) is the photoactive protein that is responsible for high light tolerance in cyanobacteria. We studied the kinetics of the OCP photocycle by monitoring changes in its absorption spectrum, intrinsic fluorescence, and fluorescence of the Nile red dye bound to OCP. It was demonstrated that all of these three methods provide the same kinetic parameters of the photocycle, namely, the kinetics of OCP relaxation in darkness was biexponential with a ratio of two components equal to 2:1 independently of temperature. Whereas the changes of the absorption spectrum of OCP characterize the geometry and environment of its chromophore, the intrinsic fluorescence of OCP reveals changes in its tertiary structure, and the fluorescence properties of Nile red indicate the exposure of hydrophobic surface areas of OCP to the solvent following the photocycle. The results of molecular-dynamics studies indicated the presence of two metastable conformations of 3′-hydroxyechinenone, which is consistent with characteristic changes in the Raman spectra. We conclude that rotation of the β-ionylidene ring in the C-terminal domain of OCP could be one of the first conformational rearrangements that occur during photoactivation. The obtained results suggest that the photoactivated form of OCP represents a molten globule-like state that is characterized by increased mobility of tertiary structure elements and solvent accessibility.

Insights into Protein Structure and Dynamics by Ultraviolet and Visible Resonance Raman Spectroscopy.

Raman spectroscopy is a form of vibrational spectroscopy based on inelastic scattering of light. In resonance Raman spectroscopy, the wavelength of the incident light falls within an absorption band of a chromophore, and this overlap of excitation and absorption energy greatly enhances the Raman scattering efficiency of the absorbing species. The ability to probe vibrational spectra of select chromophores within a complex mixture of molecules makes resonance Raman spectroscopy an excellent tool for studies of biomolecules. In this Current Topic, we discuss the type of molecular insights obtained from steady-state and time-resolved resonance Raman studies of a prototypical photoactive protein, rhodopsin. We also review recent efforts in ultraviolet resonance Raman investigations of soluble and membrane-associated biomolecules, including integral membrane proteins and antimicrobial peptides. These examples illustrate that resonance Raman is a sensitive, selective, and practical method for studying the structures of biological molecules, and the molecular bonding, geometry, and environments of protein cofactors, the backbone, and side chains.

Optogenetic determination of the myocardial requirements for extrasystoles by cell type-specific targeting of ChannelRhodopsin-2

Extrasystoles lead to several consequences, ranging from uneventful palpitations to lethal ventricular arrhythmias, in the presence of pathologies, such as myocardial ischemia. The role of working versus conducting cardiomyocytes, as well as the tissue requirements (minimal cell number) for the generation of extrasystoles, and the properties leading ectopies to become arrhythmia triggers (topology), in the normal and diseased heart, have not been determined directly in vivo. Here, we used optogenetics in transgenic mice expressing ChannelRhodopsin-2 selectively in either cardiomyocytes or the conduction system to achieve cell type-specific, noninvasive control of heart activity with high spatial and temporal resolution. By combining measurement of optogenetic tissue activation in vivo and epicardial voltage mapping in Langendorff-perfused hearts, we demonstrated that focal ectopies require, in the normal mouse heart, the simultaneous depolarization of at least 1,300-1,800 working cardiomyocytes or 90-160 Purkinje fibers. The optogenetic assay identified specific areas in the heart that were highly susceptible to forming extrasystolic foci, and such properties were correlated to the local organization of the Purkinje fiber network, which was imaged in three dimensions using optical projection tomography. Interestingly, during the acute phase of myocardial ischemia, focal ectopies arising from this location, and including both Purkinje fibers and the surrounding working cardiomyocytes, have the highest propensity to trigger sustained arrhythmias. In conclusion, we used cell-specific optogenetics to determine with high spatial resolution and cell type specificity the requirements for the generation of extrasystoles and the factors causing ectopies to be arrhythmia triggers during myocardial ischemia.

Mechanism of Orientation-Dependent Asymmetric Charge Transport in Tunneling Junctions Comprising Photosystem I.

Recently, photoactive proteins have gained a lot of attention due to their incorporation into bioinspired (photo)electrochemical and solar cells. This paper describes the measurement of the asymmetry of current transport of self-assembled monolayers (SAMs) of the entire photosystem I (PSI) protein complex (not the isolated reaction center, RCI), on two different “director SAMs” supported by ultraflat Au substrates. The director SAMs induce the preferential orientation of PSI, which manifest as asymmetry in tunneling charge-transport. We measured the oriented SAMs of PSI using eutectic Ga–In (EGaIn), a large-area technique, and conducting probe atomic force microscopy (CP-AFM), a single-complex technique, and determined that the transport properties are comparable. By varying the temperatures at which the measurements were performed, we found that there is no measurable dependence of the current on temperature from ±0.1 to ±1.0 V bias, and thus, we suggest tunneling as the mechanism for transport; there are no thermally activated (e.g., hopping) processes. Therefore, it is likely that relaxation in the electron transport chain is not responsible for the asymmetry in the conductance of SAMs of PSI complexes in these junctions, which we ascribe instead to the presence of a large, net dipole moment present in PSI.

Chemical synthesis of a two-photon-activatable chemokine and photon-guided lymphocyte migration in vivo.

Chemokine-guided lymphocyte positioning in tissues is crucial for normal operation of the immune system. Direct, real-time manipulation and measurement of single-cell responses to chemokines is highly desired for investigating the cell biology of lymphocyte migration in vivo. Here we report the development of the first two-photon-activatable chemokine CCL5 through efficient one-pot total chemical synthesis in milligram scale. By spatiotemporally controlled photoactivation, we show at the single-cell level that T cells perceive the directional cue without relying on PI3K activities, which are nonetheless required for persistent migration over an extended period of time. By intravital imaging, we demonstrate artificial T-cell positioning in cutaneous tissues and lymph nodes. This work establishes a general strategy to develop high-quality photo-activatable protein agents through tailor-designed caging of multiple residues and highlights the potential of photo-activatable chemokines for understanding and potential therapeutic manipulation of cell positioning and position-controlled cell behaviours in vivo.

Echinenone vibrational properties: From solvents to the orange carotenoid protein

Orange carotenoid protein (OCP) is a cyanobacterial photoactive protein which binds echinenone as a chromophore; it is involved in photoprotection of these photosynthetic organisms against intense illumination. In its resting state, OCP appears orange (OCPo), and turns into a red form (OCPr) when exposed to blue–green light. Here we have combined resonance Raman spectroscopy and molecular modeling to investigate the mechanisms underlying the electronic absorption properties of the different forms of OCP. Our results show that there are at least two carotenoid configurations in the OCPo, suggesting that it is quite flexible, and that the OCPo to OCPr transition must involve an increase of the apparent conjugation length of the bound echinenone. Resonance Raman indicates that this chromophore must be in an all-trans configuration in OCPo. Density functional theory (DFT) calculations, in agreement with the Raman spectra of both OCP forms, show that the OCPo to OCPr transition must involve either an echinenone s-cis to s-trans isomerization which would affect the position of its conjugated end-chain rings, or a bending of the echinenone rings which would bring them from out of the plane of the CC conjugated plane in the OCPo form into the CC plane in the OCPr form.

Stem cells can sort mitochondria by age

Stem Cells The renewal of tissues in aging organisms requires stem cells, which have the unusual ability to divide asymmetrically into one daughter cell that retains stem cell properties and another that differentiates into a particular tissue type. Katajisto et al. used photoactivated marker proteins to monitor the age of cell organelles in stemlike cells from human breast tissue and their distribution into daughter cells. Most organelles were evenly distributed, but daughter cells that maintained stem-cell properties received more newly produced mitochondria and fewer old ones. Science , this issue p. [340][1] [1]: /lookup/doi/10.1126/science.1260384

Efficient Nanostructured Biophotovoltaic Cell Based on Bacteriorhodopsin as Biophotosensitizer

Here, we report on utilizing a photoactive protein, bacteriorhodopsin (bR), as a light harvester in combination with TiO2 nanoparticles in biosensitized solar cell application. Experiments have been conducted to investigate the capability of surface adsorption of bR on nanoparticular TiO2photoanodes. Different pretreatment processes have been done to modify the interface of TiO2 nanoparticles and bR as a biophotosensitizer. Our results indicate the feasibility of efficient immobilization and photoinduced charge transfer of bR to the nanostructured TiO2 photoelectrode. Under illumination of simulated AM1.5 sunlight, the solar-light-to-electricity conversion efficiency of the designed solar cell, composed of nanoparticular and nanofibrous layers, reached up to 0.35%, with an open circuit voltage of 533 mV and photocurrent density of 1 mA cm–2. This optimized design of our bR-sensitized solar cell shows superior energy conversion efficiency in comparison to previously reported studies.