chlorophyll-c and fucoxanthin

Diatoms are a major group of algae, responsible for a quarter of the global primary production on our planet. Their adaptation to marine environments is ensured by their light-harvesting antenna - the fucoxanthin-chlorophyll protein (FCP) complex, which absorbs strongly in the blue-green spectral region. Although these essential proteins have been the subject of many studies, for a long time their comprehensive description was not possible in the absence of structural data. Last year, the 3D structures of several FCP complexes were revealed. The structure of an FCP dimer was resolved by crystallography for the pennate diatom Phaeodactylum tricornutum [W. Wang et al., Science, 2019, 363, 6427] and the structure of the PSII supercomplex from the centric diatom Chaetoceros gracilis, containing several FCPs, was obtained by electron microscopy [X. Pi et al., Science, 2019, 365, 6452; R. Nagao et al., Nat. Plants, 2019, 5, 890]. In this Perspective article, we evaluate how precisely these structures may account for previously published ultrafast spectroscopy results, describing the excitation energy transfer in the FCP from another centric diatom Cyclotella meneghiniana. Surprisingly, we find that the published FCP structures cannot explain several observations obtained from ultrafast spectroscopy. Using the available structures, and results from electron microscopy, we construct a trimer-based FCP model for Cyclotella meneghiniana, consistent with ultrafast experimental data. As a whole, our observations suggest that the structures from the proteins belonging to the FCP family display larger variations than the equivalent LHC proteins in plants, which may reflect species-specific adaptations or original strategies for adapting to rapidly changing marine environments.

Topics: Amino Acid Sequence; Chlorophyll; Chlorophyll A; Diatoms; Energy Transfer; Light-Harvesting Protein Complexes; Protein Conformation; Spectrometry, Fluorescence; Xanthophylls

Fucoxanthin-chlorophyll (Chl) a/c-binding proteins (FCPs) are light-harvesting pigment-protein complexes found in diatoms and brown algae. Due to the characteristic pigments, such as fucoxanthin and Chl c, FCPs can capture light energy in blue-to green regions. A pennate diatom Phaeodactylum tricornutum synthesizes a red-shifted form of FCP under weak or red light, extending a light-absorption ability to longer wavelengths. In the present study, we examined changes in light-harvesting and energy-transfer processes of P. tricornutum cells grown under white- and single-colored light-emitting diodes (LEDs). The red-shifted FCP appears in the cells grown under the green, yellow, and red LEDs, and exhibited a fluorescence peak around 714 nm. Additional energy-transfer pathways are established in the red-shifted FCP; two forms (F713 and F718) of low-energy Chl a work as energy traps at 77 K. Averaged fluorescence lifetimes are prolonged in the cells grown under the yellow and red LEDs, whereas they are shortened in the blue-LED-grown cells. Based on these results, we discussed the light-adaptation machinery of P. tricornutum cells involved in the red-shifted FCP.

Topics: Acclimatization; Adaptation, Physiological; Chlorophyll; Chlorophyll A; Chlorophyll Binding Proteins; Diatoms; Fluorescence; Light; Light-Harvesting Protein Complexes; Xanthophylls

Diatoms are abundant photosynthetic organisms in aquatic environments and contribute 40% of its primary productivity. An important factor that contributes to the success of diatoms is their fucoxanthin chlorophyll a/c-binding proteins (FCPs), which have exceptional light-harvesting and photoprotection capabilities. Here, we report the crystal structure of an FCP from the marine diatom

Topics: Chlorophyll; Chlorophyll A; Chlorophyll Binding Proteins; Diatoms; Energy Transfer; Light; Photosynthesis; Protein Structure, Quaternary; Thylakoids; Xanthophylls

Fucoxanthin chlorophyll (Chl) a/ c-binding proteins (FCPs) are unique light-harvesting antennas in diatoms. Recent time-resolved fluorescence analysis of photosystem I with FCP associated (PSI-FCPI) has mainly shown excitation energy transfer among Chls a from FCPI to PSI in tens of picoseconds. However, it remains unclear how each pigment, especially carotenoids and Chl c, in the FCPI is functionally related to the energy transfer in a femtosecond time range. Here, we reveal ultrafast excitation energy transfer mechanism in the PSI-FCPI preparations isolated from a diatom, Chaetoceros gracilis, by means of femtosecond time-resolved fluorescence spectroscopy with an upconversion system. Compared with the fluorescence lifetime components of PSI core-like complexes, the energy transfer of Chl c → Chl a in the FCPI was observed within hundreds of femtoseconds, and the energy in the FCPI was transferred to PSI in ∼2 ps. The comparative fluorescence analyses provide physical insights into the energy transfer machinery within FCPI and from FCPI to PSI.

Topics: Carotenoids; Chlorophyll; Chlorophyll A; Chlorophyll Binding Proteins; Diatoms; Energy Transfer; Fluorescence; Photosystem I Protein Complex; Spectrometry, Fluorescence; Xanthophylls

The major light-harvesting pigment protein complex (fucoxanthin-chlorophyll-binding protein complex; FCP) was purified from a marine centric diatom, Chaetoceros gracilis, by mild solubilization followed by sucrose density gradient centrifugation, and then characterized. The dynamic light scattering measurement showed unimodality, indicating that the complex was highly purified. The amount of chlorophyll a (Chl a) bound to the purified FCP accounted for more than 60 % of total cellular Chl a. The complex was composed of three abundant polypeptides, although there are nearly 30 FCP-related genes. The two major components were identified as Fcp3 (Lhcf3)- and Fcp4 (Lhcf4)-equivalent proteins based on their internal amino acid sequences and a two-dimensional isoelectric focusing electrophoresis analysis developed in this work. Compared with the thylakoids, the FCP complex showed higher contents of fucoxanthin and chlorophyll c but lower contents of the xanthophyll cycle pigments diadinoxanthin and diatoxanthin. Fluorescence excitation spectra analyses indicated that light harvesting, rather than photosystem protection, is the major function of the purified FCP complex, which is associated with more than 60 % of total cellular Chl a. These findings suggest that the huge amount of Chl bound to the FCP complex composed of Lhcf3, Lhcf4, and an unidentified minor protein has a light-harvesting function to allow efficient photosynthesis under the dim-light conditions in the ocean.

Topics: Carrier Proteins; Chlorophyll; Chlorophyll A; Diatoms; Light; Light-Harvesting Protein Complexes; Photosystem II Protein Complex; Spectrometry, Fluorescence; Thylakoids; Xanthophylls

The fucoxanthin chlorophyll a/c-binding protein (FCP) is a unique antenna complex possessed by diatoms. Although FCP complexes have been isolated from various diatoms, there is no direct evidence for the existence of FCP associated with photosystem II (FCPII). Here, we report the isolation and spectroscopic characterization of FCPII complex from the diatom Chaetoceros gracilis. The FCPII complex was purified using sucrose centrifugation and anion-exchange chromatography. Clear-native PAGE and SDS-PAGE analyses revealed that the FCPII complex was composed of FCP-A oligomer and FCP-B/C trimer. Time-resolved fluorescence spectra of the FCPII complex were measured at 77 K. The characteristic lifetimes and fluorescence components were determined using global fitting analysis, followed by the construction of fluorescence decay-associated spectra (FDAS). FDAS exhibited fluorescence rises and decays, reflecting excitation energy transfer, with the time constants of 150 ps, 800 ps, and 2.9 ns. The long time constants are most likely attributed to the intercomplex excitation energy transfer between FCP-A oligomer and FCP-B/C trimer in the FCPII complex. The 5.6 ns FDAS likely originates from the final energy traps. In contrast, the FDAS exhibited no quenching component with any time constant. These results indicate that the FCPII complex is efficient in light harvesting and excitation energy transfer.

Topics: Centrifugation, Density Gradient; Chlorophyll; Chlorophyll A; Chromatography, Ion Exchange; Diatoms; Light; Photosynthesis; Photosystem II Protein Complex; Protein Multimerization; Xanthophylls

The fucoxanthin chlorophyll (Chl) a/c-binding protein (FCP) is responsible for excellent light-harvesting strategies that enable survival in fluctuating light conditions. Here, we report the light-harvesting and quenching states of two FCP complexes, FCP-A and FCP-B/C, isolated from the diatom Chaetoceros gracilis. Pigment analysis revealed that FCP-A is enriched in Chl c, whereas FCP-B/C is enriched in diadinoxanthin, reflecting differences in low-temperature steady-state absorption and fluorescence spectra of each FCP complex. Time-resolved fluorescence spectra were measured at 77 K, and the characteristic lifetimes were determined using global fitting analysis of the spectra. Tens of picosecond (ps) components revealed energy transfer to low-energy Chl a from Chls a and c, whereas the other components showed only fluorescence decay components with no concomitant rise components. The normalized amplitudes of hundreds of picosecond components were relatively 30% in the total fluorescence, whereas those of longest-lived components were 60%. The hundreds of picosecond components were assigned as excitation energy quenching, whereas the longest-lived components were assigned as fluorescence from the final energy traps. These results suggest that 30% of FCP complex forming quenching state and the other 60% of FCP complex forming light-harvesting state exist heterogeneously in each FCP fraction under continuous low-light condition.

Topics: Chlorophyll; Chlorophyll A; Diatoms; Light-Harvesting Protein Complexes; Spectrometry, Fluorescence; Temperature; Xanthophylls

Chlorophylls (Chls)-a and -c(2) are identified and characterized in fucoxanthin chlorophyll-a/c(2) protein (FCP) complexes in the trimeric (FCPa(trim)) and oligomeric (FCPb(olig)) forms of FCP from the diatom Cyclotella meneghiniana using resonance Raman (RR) spectroscopy. Importantly, two different Chl-c(2)s are identified in both FCPa(trim) and FCPb(olig) from their signature ring-breathing modes at approximately 1360 cm(-1). In addition, the C13(1)-keto carbonyl peaks indicate the presence of more than four Chl-a's in both FCP complexes and are broadly classified into three groups with strong, medium and weak external hydrogen bonds. Together, they provide the strongest spectroscopic evidence so far that there may be up to double the number of pigments previously estimated at 4Fx:4Chl-a:1Chl-c(2) per FCP monomer. Careful analysis of the protein sequences also strongly support the higher pigment content by showing that at least six Chl-a, and one Chl-b, binding sites found in LHCII are retained in the FCPs. The relative enhancement of the RR bands for 406.7 versus 413.1 nm further allows some distinction of blue- versus red-absorbing Chl-a's, respectively. Further differences between the Chls in FCPb(olig) and FCPa(trim) are present in the amino-acid sequences and the RR signals. Information about the Chl-binding sites, complemented by information about the structures and interactions of the Chls are used to characterize their local environments, and assign pigment locations (and functions) in FCPb(olig) and FCPa(trim), which along with the earlier characterization of the carotenoids (J. Phys. Chem. B. 112 (2009) 12565-12574) provide a first (global) framework for pigment organization in FCP.

Topics: Amino Acid Sequence; Binding Sites; Chlorophyll; Chlorophyll A; Diatoms; Models, Molecular; Molecular Sequence Data; Pigments, Biological; Sequence Alignment; Spectrum Analysis, Raman; Xanthophylls

In the present study we report that in the diatom Cyclotella meneghiniana the diatoxanthin-dependent non-photochemical quenching of chlorophyll fluorescence (NPQ) is heterogeneous and consists of three different components. (i) A transient NPQ component that generates immediately upon illumination, depends on the transthylakoid proton gradient as well as on the light intensity, and is modulated by the initial diatoxanthin content of the cells. It is located in the antenna complexes of C. meneghiniana and is comparable with the transient NPQ observed in vascular plants. (ii) A steady-state NPQ component is observed during later stages of the high-light illumination and depends on the diatoxanthin content formed by the light-activated diadinoxanthin cycle. (iii) A fast relaxing NPQ component is seen upon a transition of high-light-illuminated cells to complete darkness. This component relaxes within a time frame of tens of seconds and its extent is correlated with the amount of diatoxanthin formed during the phase of actinic illumination. It cannot be observed in dithiothreitol-treated cells where the de-epoxidation of diadinoxanthin to diatoxanthin is suppressed. The fast relaxing component can be interpreted as a relaxation of part of the steady-state NPQ. The different diatoxanthin-dependent components are characterized by different quenching efficiencies of diatoxanthin. Diatoxanthin involved in the transient NPQ exhibits a 2-fold higher quenching efficiency compared with diatoxanthin participating in the steady-state NPQ. It is proposed that the different quenching efficiencies of diatoxanthin are caused by the existence of different diatoxanthin pools within the antenna system of C. meneghiniana.

Topics: beta Carotene; Chlorophyll; Diatoms; Fluorescence; Light; Photosynthesis; Signal Transduction; Time Factors; Xanthophylls

In the present study we investigate how intraspecific (density-dependent) competition for nutrients by the diatom Nitzschia microcephala affects the level of oxidative stress in the algal cells as well as their production of pigments and thiamine. N. microcephala was grown in three different densities until the stationary growth phase was reached. Throughout the experiment, growth rate was negatively related to cell density. Superoxide dismutase activity, protein thiol, and diatoxanthin concentrations indicated increasing oxidative stress with increasing cell density, which was most probably caused by nutrient depletion of the medium. Pigment contents per cell (except for diatoxanthin) decreased with increasing cell density. N. microcephala was able to synthesize thiamine and its thiamine content per cell increased in concert with cell density. In comparison, the dinoflagellate Amphidinium carterae was unable to synthesize thiamine. These results suggest that cells of N. microcephala subjected to higher competition and lower growth rates have a lower carotenoid content and a higher thiamine content. If such responses would occur in nature as well, eutrophication (higher cell densities) may alter the quality of microalgae as food items for higher trophic levels not only by species shifts in the phytoplankton, but also by changes in the cellular nutritional value within species.

Topics: Animals; Chlorophyll; Chlorophyll A; Diatoms; Dinoflagellida; Eutrophication; Oxidative Stress; Sulfhydryl Compounds; Superoxide Dismutase; Thiamine; Xanthophylls

Resonance Raman spectroscopy of an antenna protein from the brown alga Laminaria saccharina has been used to investigate the molecular structure of this light-harvesting complex (LHC) at the level of its bound pigments, chlorophylls (chl) a and c and the xanthophyll fucoxanthin. Evidence has been obtained for the conservation of pigment structure during the isolation procedure used. Six chl a and two chl c molecules are indicated from the positions and relative contributions of stretching modes of their keto-carbonyl groups. Of special interest is the presence of a population of chls a having a protein-binding conformation highly similar to that seen in antenna proteins from higher plants, possibly indicating a common structural motif within this extended gene family. The eight fucoxanthin molecules evidenced are all in the all-trans conformation; however, one or two have a highly twisted configuration. The results are discussed in terms of common and varying structural features of LHCs in higher plants and algae.

Topics: Binding Sites; Carotenoids; Chlorophyll; Chlorophyll A; Laminaria; Light-Harvesting Protein Complexes; Molecular Conformation; Photosynthetic Reaction Center Complex Proteins; Protein Conformation; Spectrum Analysis, Raman; Xanthophylls

A fucoxanthin-chlorophyll protein (FCP) cDNA from the raphidophyte Heterosigma carterae encodes a 210-amino acid polypeptide that has similarity to other FCPs and to the chlorophyll a/b-binding proteins (CABs) of terrestrial plants and green algae. The putative transit sequence has characteristics that resemble a signal sequence. The Heterosigma fcp genes are part of a large multigene family which includes members encoding at least two significantly different polypeptides (Fcp1, Fcp2). Comparison of the FCP sequences to the recently determined three-dimensional structure of the pea LHC II complex indicates that many of the key amino acids thought to participate in the binding of chlorophyll and the formation of complex-stabilizing ionic interactions are well conserved. Phylogenetic analyses of sequences of light-harvesting proteins shows that the FCPs of several chromophyte phyla form a natural group separate from the intrinisic peridinin-chlorophyll proteins (iPCPs) of the dinoflagellates: Although the FCP and CAB genes shared a common ancestor, these lineages diverged from each other prior to the separation of the CAB LHC I and LHC II sequences in the green algae and terrestrial plants.

Topics: Amino Acid Sequence; Carotenoids; Chlorophyll; Chlorophyll A; DNA, Complementary; Eukaryota; Evolution, Molecular; Light-Harvesting Protein Complexes; Models, Molecular; Molecular Sequence Data; Photosynthetic Reaction Center Complex Proteins; Phylogeny; Protein Conformation; Sequence Homology, Amino Acid; Xanthophylls

We investigated the primary structure of a cDNA encoding a light-harvesting protein from the marine chrysophyte Isochrysis galbana. Antibodies raised against the major fucoxanthin, chlorophyll a/c-binding light-harvesting protein (FCP) of I. galbana were used to select a cDNA clone encoding one of the FCP apoproteins. The nucleic acid and deduced amino acid sequences reveal conserved regions within the first and third transmembrane spans with Chl a/b-binding proteins and with FCPs of another chromophyte. However, the amino acid identity between I. galbana FCP and other cab genes of FCPs is only ca. 30%. Phylogenetic analyses demonstrated that the FCP genes of both diatoms and chrysophytes sequenced to date are more closely related to cab genes encoding LHC I, CP 29, and CP 24 of higher plants than to cab genes encoding LHC II of chlorophytes. We propose that LHC I, CP 24 and CP 29 and FCP might have originated from a common ancestral chl binding protein and that the major LHC II of Chl a/b-containing organisms arose after the divergence between the chromophytes and the chlorophytes.

Topics: Amino Acid Sequence; Apoproteins; Biological Evolution; Carotenoids; Chlorophyll; Chlorophyll A; Cross Reactions; Eukaryota; Genes, Plant; Light-Harvesting Protein Complexes; Molecular Sequence Data; Multigene Family; Photosynthetic Reaction Center Complex Proteins; Sequence Homology, Amino Acid; Xanthophylls

The N-terminus of the major polypeptide component of the light-harvesting complex (LHC) from the brown alga Laminaria saccharina is blocked. Two partial sequences, one near the N-terminus and the other near the C-terminus, have been obtained by chemical cleavage with acetic acid and N-chlorosuccinimide. Four peptides were separated after trypsin digestion of the thylakoid membranes. One fragment is not phosphorylated, is not blocked, and has been sequenced. Purification on a reversed-phase column showed two forms of the LHC protein: the more hydrophobic form appears to be bound to photosystem I. These results are compared with LHC from other Chromophytes and the CAB family of green plants.

Topics: Amino Acid Sequence; Aspartic Acid; Carotenoids; Chlorophyll; Chlorophyll A; Chloroplasts; Intracellular Membranes; Laminaria; Light-Harvesting Protein Complexes; Molecular Sequence Data; Peptide Fragments; Phosphorylation; Photosynthetic Reaction Center Complex Proteins; Photosystem I Protein Complex; Proline; Sequence Analysis; Succinimides; Trypsin; Xanthophylls