Light-harvesting Carotenoids Research Articles

Valuable pigments from microalgae: phycobiliproteins, primary carotenoids, and fucoxanthin.

Phycobiliproteins, carotenoids and fucoxanthin are photosynthetic pigments extracted from microalgae and cyanobacteria with great potential biotechnological applications, as healthy food colorants and cosmetics. Phycocyanin possesses a brilliant blue color, with fluorescent properties making it useful as a reagent for immunological essays. The most important source of phycocyanin is the cyanobacterium Arthrospira platensis, however, recently, the Rhodophyta Galdieria sulphuraria has also been identified as such. The main obstacle to the commercialization of phycocyanin is represented by its chemical instability, strongly reducing its shelf-life. Moreover, the high level of purity needed for pharmaceutical applications requires several steps which increase both the production time and cost. Microalgae (Chlorella, Dunaliella, Nannochloropsis, Scenedesmus) produce several light harvesting carotenoids, and are able to manage with oxidative stress, due to their free radical scavenging properties, which makes them suitable for use as source of natural antioxidants. Many studies focused on the selection of the most promising strains producing valuable carotenoids and on their extraction and purification. Among carotenoids produced by marine microalgae, fucoxanthin is the most abundant, representing more than 10% of total carotenoids. Despite the abundance and diversity of fucoxanthin producing microalgae only a few species have been studied for commercial production, the most relevant being Phaeodactylum tricornutum. Due to its antioxidant activity, fucoxanthin can bring various potential benefits to the prevention and treatment of lifestyle-related diseases. In this review, we update the main results achieved in the production, extraction, purification, and commercialization of these important pigments, motivating the cultivation of microalgae as a source of natural pigments.

Expression of Xanthorhodopsin in Escherichia coli.

Xanthorhodopsin (XR) from Salinibacter ruber is a light-driven proton pump containing retinal and a light-harvesting carotenoid antenna salinixanthin. Previous structure-functional studies of XR were conducted using a protein isolated from the native host only due to the absence of heterologous expression in Escherichia coli. In this paper, we describe cell-free synthesis and incorporation in lipid-protein nanodiscs of the recombinant XR that demonstrated its principal compatibility with E. coli biosynthetic machinery. To produce XR in E. coli, three C-terminal deletion variants of this protein were constructed. In contrast to the full-length XR, their expression resulted in efficient synthesis in E. coli cells. However, cells producing recombinant XR variants bound retinal only upon growth in minimal medium, not in the rich one. The XR3 variant with deletion of ten C-terminal amino acid residues was obtained and characterized. Its absorption spectrum and photocycle kinetics were close to those reported for XR isolated from S. ruber membranes and bleached from salinixanthin. We have also constructed the first mutants of XR, H62M and D96N, and examined their properties.

Phototrophy by antenna-containing rhodopsin pumps in aquatic environments.

Energy transfer from light-harvesting ketocarotenoids to the light-driven proton pump xanthorhodopsins has been previously demonstrated in two unique cases: an extreme halophilic bacterium1 and a terrestrial cyanobacterium2. Attempts to find carotenoids that bind and transfer energy to abundant rhodopsin proton pumps3 from marine photoheterotrophs have thus far failed4-6. Here we detected light energy transfer from the widespread hydroxylated carotenoids zeaxanthin and lutein to the retinal moiety of xanthorhodopsins and proteorhodopsins using functional metagenomics combined with chromophore extraction from the environment. The light-harvesting carotenoids transfer up to 42% of the harvested energy in the violet- or blue-light range to the green-light absorbing retinal chromophore. Our data suggest that these antennas may have asubstantial effect on rhodopsin phototrophy in the world's lakes, seas and oceans. However, the functional implications of our findings are yet to be discovered.

Light induces peridinin and docosahexaenoic acid accumulation in the dinoflagellate Durusdinium glynnii.

Peridinin is a light-harvesting carotenoid present in phototrophic dinoflagellates and has great potential for new drug applications and cosmetics development. Herein, the effects of irradiance mediated by light-emitting diodes on growth performance, carotenoid and fatty acid profiles, and antioxidant activity of the endosymbiotic dinoflagellate Durusdinium glynnii were investigated. The results demonstrate that D. glynnii is particularly well adapted to low-light conditions; however, it can be high-light-tolerant. In contrast to other light-harvesting carotenoids, the peridinin accumulation in D. glynnii occurred during high-light exposure. The peridinin to chlorophyll-a ratio varied as a function of irradiance, while the peridinin to total carotenoids ratio remained stable. Under optimal irradiance for growth, there was a peak in docosahexaenoic acid (DHA) bioaccumulation. This study contributes to the understanding of the photoprotective role of peridinin in endosymbiont dinoflagellates and highlights the antioxidant activity of peridinin-rich extracts. KEY POINTS: • Peridinin has a protective role against chlorophyll photo-oxidation • High light conditions induce cellular peridinin accumulation • D. glynnii accumulates high amounts of DHA under optimal light supply.

Correction to "Quantum Coherent Excitation Energy Transfer by Carotenoids in Photosynthetic Light Harvesting".

ADVERTISEMENT RETURN TO ISSUEPREVAddition/CorrectionNEXTORIGINAL ARTICLEThis notice is a correctionCorrection to “Quantum Coherent Excitation Energy Transfer by Carotenoids in Photosynthetic Light Harvesting”Jerome D. RoscioliJerome D. RoscioliMore by Jerome D. Roscioli, Soumen GhoshSoumen GhoshMore by Soumen Ghoshhttp://orcid.org/0000-0002-3323-1724, Amy M. LaFountainAmy M. LaFountainMore by Amy M. LaFountain, Harry A. FrankHarry A. FrankMore by Harry A. Frank, and Warren F. Beck*Warren F. BeckMore by Warren F. Beckhttp://orcid.org/0000-0002-7491-0264Cite this: J. Phys. Chem. Lett. 2018, 9, 15, 4436Publication Date (Web):July 24, 2018Publication History Published online24 July 2018Published inissue 2 August 2018https://doi.org/10.1021/acs.jpclett.8b02230Copyright © 2018 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views619Altmetric-Citations-LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (421 KB) Get e-Alerts Get e-Alerts

Peridinin Torsional Distortion and Bond-Length Alternation Introduce Intramolecular Charge-Transfer and Correlated Triplet Pair Intermediate Excited States.

The nature of intramolecular charge transfer (ICT) and the mechanism of intramolecular singlet fission (SF) in peridinin remain open research questions. Obtaining an understanding of the population evolution from the bright state to dark state following a photoinduced electronic transition is critical. Unambiguously describing this evolution in peridinin, and light-harvesting carotenoids in general, has proven elusive experimentally and computationally. To offer a balanced description of the bright- and dark-state electronic structures, we here apply ab initio multireference perturbation theory quantum chemistry-the density matrix renormalization group self-consistent field and complete-active-space self-consistent field with second-order N-electron valence perturbation theory. At traditional bright- (S2) and dark-state (S1) optimized geometries, we find that an additional correlated triplet pair state and ICT state are derived from the canonical polyene Bu (S3) and 3Ag (S4) dark singlet excited states, respectively. Whereas the S3 state's physical properties are insensitive to peridinin's allene-tail donor and lactone ring acceptor functionalization, the S4 state exhibits a markedly enhanced oscillator strength and highest occupied molecular orbital-lowest unoccupied molecular orbital transition density. These changes suggest that the ICT character stems from mixing between the bright S2 and putatively dark S4.

The [formula omitted] state falls below [formula omitted] at carotenoid-relevant conjugation lengths

Spectroscopy of all-trans linear polyenes is characterized by a one-photon electronic transition to a bright S2 state and two-photon transition to a lower-lying dark S1 state. We apply ab initio quantum chemistry to distinguish additional diffuse dark singlet states. Building on a systematic implementation of CASSCF and DMRGSCF coupled to strongly-contracted NEVPT2, we report the excitation energies for a series of polyenes from butadiene to C16H18 at optimized S0, S1 and S2 geometries. Ionic/covalent state inversion within each manifold is identified at seven conjugated double bonds, making the Bu- a dark intermediate state at its optimized geometry and the Ag+ the S3 state at the S0 optimized geometry. The relevance of these results to the function of carotenoids in photosynthetic light harvesting is discussed.

A functional zeaxanthin epoxidase from red algae shedding light on the evolution of light‐harvesting carotenoids and the xanthophyll cycle in photosynthetic eukaryotes

The epoxy-xanthophylls antheraxanthin and violaxanthin are key precursors of light-harvesting carotenoids and participate in the photoprotective xanthophyll cycle. Thus, the invention of zeaxanthin epoxidase (ZEP) catalyzing their formation from zeaxanthin has been a fundamental step in the evolution of photosynthetic eukaryotes. ZEP genes have only been found in Viridiplantae and chromalveolate algae with secondary plastids of red algal ancestry, suggesting that ZEP evolved in the Viridiplantae and spread to chromalveolates by lateral gene transfer. By searching publicly available sequence data from 11 red algae covering all currently recognized red algal classes we identified ZEP candidates in three species. Phylogenetic analyses showed that the red algal ZEP is most closely related to ZEP proteins from photosynthetic chromalveolates possessing secondary plastids of red algal origin. Its enzymatic activity was assessed by high performance liquid chromatography (HPLC) analyses of red algal pigment extracts and by cloning and functional expression of the ZEP gene from Madagascaria erythrocladioides in leaves of the ZEP-deficient aba2 mutant of Nicotiana plumbaginifolia. Unlike other ZEP enzymes examined so far, the red algal ZEP introduces only a single epoxy group into zeaxanthin, yielding antheraxanthin instead of violaxanthin. The results indicate that ZEP evolved before the split of Rhodophyta and Viridiplantae and that chromalveolates acquired ZEP from the red algal endosymbiont and not by lateral gene transfer. Moreover, the red algal ZEP enables engineering of transgenic plants incorporating antheraxanthin instead of violaxanthin in their photosynthetic machinery.

Quantum Coherent Excitation Energy Transfer by Carotenoids in Photosynthetic Light Harvesting.

It remains an open question whether quantum coherence and molecular excitons created by delocalization of electronic excited states are essential features of the mechanisms that enable efficient light capture and excitation energy transfer to reaction centers in photosynthetic organisms. The peridinin-chlorophyll a protein from marine dinoflagellates is an example of a light-harvesting system with tightly clustered antenna chromophores in which quantum coherence has long been suspected, but unusually it features the carotenoid peridinin as the principal light absorber for mid-visible photons. We report that broad-band two-dimensional electronic spectroscopy indeed reveals the initial presence of exciton relaxation pathways that enable transfer of excitation from peridinin to chlorophyll a in <20 fs, but the quantum coherence that permits this is very short-lived. Strongly coupled excited-state vibrational distortions of the peridinins trigger a dynamic transition of the electronic structure of the system and a rapid conversion to incoherent energy transfer mechanisms.

Enhanced Output from Biohybrid Photoelectrochemical Transparent Tandem Cells Integrating Photosynthetic Proteins Genetically Modified for Expanded Solar Energy Harvesting

A transparent biohybrid photoelectrochemical tandem cell is developed by employing optically-complementary variants of a photosynthetic protein in a stacked tandem architecture that utilizes a conductive polymer, poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS), as a transparent counter electrode. The tandem design demonstrates the photocurrent enhancement by complementary absorption of two naturally-occurring red and green versions of a bacterial Reaction center/Light Harvesting protein (RC-LH1) that vary in the type of light harvesting carotenoid feeding the central reaction center module with excited state energy. The use of PEDOT:PSS electrode results in a 12-fold improvement in photocurrent compared to that achievable with Platinum.

Structural and Functional Studies of a Newly Grouped Haloquadratum walsbyi Bacteriorhodopsin Reveal the Acid-resistant Light-driven Proton Pumping Activity

Retinal bound light-driven proton pumps are widespread in eukaryotic and prokaryotic organisms. Among these pumps, bacteriorhodopsin (BR) proteins cooperate with ATP synthase to convert captured solar energy into a biologically consumable form, ATP. In an acidic environment or when pumped-out protons accumulate in the extracellular region, the maximum absorbance of BR proteins shifts markedly to the longer wavelengths. These conditions affect the light-driven proton pumping functional exertion as well. In this study, wild-type crystal structure of a BR with optical stability under wide pH range from a square halophilic archaeon, Haloquadratum walsbyi (HwBR), was solved in two crystal forms. One crystal form, refined to 1.85 Å resolution, contains a trimer in the asymmetric unit, whereas another contains an antiparallel dimer was refined at 2.58 Å. HwBR could not be classified into any existing subgroup of archaeal BR proteins based on the protein sequence phylogenetic tree, and it showed unique absorption spectral stability when exposed to low pH values. All structures showed a unique hydrogen-bonding network between Arg(82) and Thr(201), linking the BC and FG loops to shield the retinal-binding pocket in the interior from the extracellular environment. This result was supported by R82E mutation that attenuated the optical stability. The negatively charged cytoplasmic side and the Arg(82)-Thr(201) hydrogen bond may play an important role in the proton translocation trend in HwBR under acidic conditions. Our findings have unveiled a strategy adopted by BR proteins to solidify their defenses against unfavorable environments and maintain their optical properties associated with proton pumping.

Physiological responses of Zostera marina and Cymodocea nodosa to light-limitation stress.

The effects of light-limitation stress were investigated in natural stands of the seagrasses Zostera marina and Cymodocea nodosa in Ria Formosa coastal lagoon, southern Portugal. Three levels of light attenuation were imposed for 3 weeks in two adjacent meadows (2–3 m depth), each dominated by one species. The response of photosynthesis to light was determined with oxygen electrodes. Chlorophylls and carotenoids were determined by high-pressure liquid chromatography (HPLC). Soluble protein, carbohydrates, malondialdehyde and phenol contents were also analysed. Both species showed evident signs of photoacclimation. Their maximum photosynthetic rates were significantly reduced with shading. Ratios between specific light harvesting carotenoids and the epoxidation state of xanthophyll cycle carotenoids revealed significantly higher light harvesting efficiency of C. nodosa, a competitive advantage in a low light environment. The contents of both soluble sugars and starch were considerably lower in Z. marina plants, particularly in the rhizomes, decreasing even further with shading. The different carbohydrate energy storage strategies found between the two species clearly favour C. nodosa's resilience to light deprivation, a condition enhanced by its intrinsic arrangement of the pigment pool. On the other hand, Z. marina revealed a lower tolerance to light reduction, mostly due to a less plastic arrangement of the pigment pool and lower carbohydrate storage. Our findings indicate that Z. marina is close to a light-mediated ecophysiological threshold in Ria Formosa.

Thermal and Spectroscopic Characterization of a Proton Pumping Rhodopsin from an Extreme Thermophile

So far retinylidene proteins (∼rhodopsin) have not been discovered in thermophilic organisms. In this study we investigated and characterized a microbial rhodopsin derived from the extreme thermophilic bacterium Thermus thermophilus, which lives in a hot spring at around 75 °C. The gene for the retinylidene protein, named thermophilic rhodopsin (TR), was chemically synthesized with codon optimization. The codon optimized TR protein was functionally expressed in the cell membranes of Escherichia coli cells and showed active proton transport upon photoillumination. Spectroscopic measurements revealed that the purified TR bound only all-trans-retinal as a chromophore and showed an absorption maximum at 530 nm. In addition, TR exhibited both photocycle kinetics and pH-dependent absorption changes, which are characteristic of rhodopsins. Of note, time-dependent thermal denaturation experiments revealed that TR maintained its absorption even at 75 °C, and the denaturation rate constant of TR was much lower than those of other proton pumping rhodopsins such as archaerhodopsin-3 (200 ×), Haloquadratum walsbyi bacteriorhodopsin (by 10-times), and Gloeobacter rhodopsin (100 ×). Thus, these results suggest that microbial rhodopsins are also distributed among thermophilic organisms and have high stability. TR should allow the investigation of the molecular mechanisms of ion transport and protein folding.

Shedding New Light on Retinal Protein Photochemistry

The ultrafast spectroscopic investigation of novel retinal proteins challenges existing notions concerning the course of primary events in these natural photoreceptors. We review two illustrations here. The first demonstrates that changes in the initial retinal configuration can alter the duration of photochemistry by nearly an order of magnitude in Anabaena sensory rhodopsin, making it as rapid as the ballistic photoisomerization in visual pigments. This prompted a reinvestigation of the much studied bacteriorhodopsin, leading to a similar trend as well, contrary to earlier reports. The second involves the study of xanthorhodopsin, an archaeal proton pump that includes an attached light-harvesting carotenoid. Pump-probe experiments demonstrate the efficient transfer of energy from carotenoid to retinal, providing a first glimpse at a cooperative multichromophore function, which is probably characteristic of many other proteins as well. Finally, we discuss measures required to advance our knowledge from kinetics to mode-specific dynamics concerning this expanding family of biological photoreceptors.

Interaction of Antenna Carotenoid and Retinal in the Light-Driven Pumps of Salinibacter Ruber and Gloeobacter Violaceus

Xanthorhodopsin is a light-driven proton pump like bacteriorhodopsin, but contains a second chromophore, salinixanthin, a carotenoid. Action spectra for transport and fluorescence of the retinal upon excitation of salinixanthin, as well as femtosecond kinetics of carotenoid fluorescence, indicate that the carotenoid functions as an antenna to the retinal, with ca. 50% efficiency for excited-state energy transfer. The resulting charge redistribution in the retinal and the local electric field produced, in the excited state and in the primary stable photoproduct K, in turn, causes distinct electrochromic shifts in the carotenoid spectrum. The close interaction of carotenoid and retinal suggests that the two chromophores are in proximity. Tight binding of the carotenoid, as indicated by its sharpened vibration bands and intense induced circular dichroism in the visible, is removed in the absence of the retinal, and restored upon reconstitution with retinal or retinal analogues. The crystallographic structure of the xanthorhodopsin at 1.9 A resolution identifies the location of the chromophores. The structural model from x-ray diffraction reveals that the ring moieties of the retinal and the carotenoid are at nearly van der Waals distance from one another. Salinixanthin and one of the native carotenoids of Gloeobacter, echinenone, bind to gloeorhodopsin expressed in E. coli, and the complex shows excited-state energy exchange much like xanthorhodopsin. Protein sequences and mutational studies in Gloeobacter indicate that binding of the carotenoid depends on a conserved glycine at the keto-ring, which is a tryptophan in bacteriorhodopsin and other archaeal rhodopsins. On this basis, numerous otherwise unrelated eubacterial rhodopsins are predicted to contain light-harvesting carotenoids.

Algal Biogeography: Metagenomics Shows Distribution of a Picoplanktonic Pelagophyte

How can we determine the distribution of uncultured marine microorganisms? Targeted metagenomics has provided the complete chloroplast genome sequence, and the distribution, for a picoplanktonic pelagophyte alga.

Unique carotenoid lactoside, P457, in Symbiodinium sp. of dinoflagellate.

The dinoflagellates are a large group of unicellular alge in marine and fresh water. Some are an endosymbiont of marine animals. Photosynthetic dinoflagellates have peridinin, a light-harvesting carotenoid. In addition, a unique carotenoid, P457, was found from Amphinidium. The presence of P457 in Symbiodinium derived from marine animals has not been reported. We reconfirmed the molecular structure of P457, a neoxanthin-like carotenoid with an aldehyde group and a lactoside, from Symbiodinium sp. NBRC 104787 isolated from a sea anemone. In addition, we investigated the distribution of P457 and peridinin in various Symbiodinium and scleractinian coral species, and possible biosynthetic pathways of these carotenoids are proposed.

Syntheses of ylidenbutenolide-modified derivatives of peridinin and their stereochemical and spectral characteristics

Peridinin is a light-harvesting carotenoid found in oceanic photosynthetic organisms. It possesses a unique gamma-ylidenbutenolide function and engages in energy transfer to chlorophyll a with very high (>90%) efficiency. In order to examine the relationship between the unique structure of peridinin and its facility in carrying out energy transfer, we have synthesized two different ylidenbutenolide-modified derivatives of peridinin. In this communication, the details of the syntheses are described as are the stereochemical and spectral characteristics of the derivatives; the novel ylidenbutenolide functional group stabilizes the molecule and maintains the conjugated pi-electron system in an all-trans configuration.

Reconstitution of Gloeobacter violaceus Rhodopsin with a Light-Harvesting Carotenoid Antenna

We show that salinixanthin, the light-harvesting carotenoid antenna of xanthorhodopsin, can be reconstituted into the retinal protein from Gloeobacter violaceus expressed in Escherichia coli. Reconstitution of gloeobacter rhodopsin with the carotenoid is accompanied by characteristic absorption changes and the appearance of CD bands similar to those observed for xanthorhodopsin that indicate immobilization and twist of the carotenoid in the binding site. As in xanthorhodopsin, the carotenoid functions as a light-harvesting antenna. The excitation spectrum for retinal fluorescence emission shows that ca. 36% of the energy absorbed by the carotenoid is transferred to the retinal. From excitation anisotropy, we calculate the angle between the two chromophores as being ca. 50 degrees , similar to that in xanthorhodopsin. The results indicate that gloeobacter rhodopsin binds salinixanthin in a manner similar to that of xanthorhodopsin and suggest that it might bind a carotenoid also in vivo. In the crystallographic structure of xanthorhodopsin, the conjugated chain of the carotenoid lies on the surface of helices E and F, and the 4-keto ring is immersed in the protein at van der Waals distance from the ionone ring of the retinal. The 4-keto ring is in the space occupied by a tryptophan in bacteriorhodopsin, which is replaced by the smaller glycine in xanthorhodopsin and gloeobacter rhodopsin. Specific binding of the carotenoid and its light-harvesting function are eliminated by a single mutation of the gloeobacter protein that replaces this glycine with a tryptophan. This indicates that the 4-keto ring is critically involved in carotenoid binding and suggests that a number of other recently identified retinal proteins, from a diverse group of organisms, could also contain carotenoid antenna since they carry the homologous glycine near the retinal.

High production of unexpected carotenoids in Dinophyceae. Astaxanthin esters from the freshwater dinoflagellate Tovellia sanguinea

A wide range of photopigments biosynthesised by a unialgal cell culture of the red dinoflagellate Tovellia sanguinea, the blooms of which were responsible for the summer reddening of the waters of the Lake Tovel until 1964, have been identified through reversed-phase high pressure liquid chromatography (HPLC) coupled to photodiode array detector (PDAD) and to atmospheric pressure ionisation mass spectrometer (API-MS). Myristoyl and palmitoyl astaxanthin esters were the most abundant pigments of T. sanguinea, whereas other carotenoids, considered to be diagnostic markers for dinoflagellates, were present here only in relatively low amounts. This is the first report where astaxanthin esters have been found as the major pigments in the taxon Dinoflagellata and largely over-expressed in comparison to the light-harvesting carotenoid peridinin. A plausible biogenetic route for the ketocarotenogenesis of T. sanguinea pigments is proposed.