Reconstitution of the peridinin-chlorophyll a protein (PCP): evidence for functional flexibility in chlorophyll binding

Chlorophyll f can replace chlorophyll a in the soluble antenna of dinoflagellates

Chlorophyll f is a new type of chlorophyll isolated from cyanobacteria. The absorption and fluorescence characteristics of chlorophyll f permit these oxygenic-photosynthetic organisms to thrive in environments where white light is scarce but far-red light is abundant. To explore the ligand properties of chlorophyll f and its energy transfer profiles we established two different in vitro reconstitution systems. The reconstituted peridinin-chlorophyll f protein complex (chlorophyll f-PCP) showed a stoichiometry ratio of 4:1 between peridinin and chlorophyll f, consistent with the peridinin:chlorophyll a ratio from native PCP complexes. Using emission wavelength at 712 nm, the excitation fluorescence featured a broad peak at 453 nm and a shoulder at 511 nm confirming energy transfer from peridinin to chlorophyll f. In addition, by using a synthetic peptide mimicking the first transmembrane helix of light-harvesting chlorophyll proteins of plants, we report that chlorophyll f, similarly to chlorophyll b, did not interact with the peptide contrarily to chlorophyll a, confirming the accessory role of chlorophyll f in photosystems. The binding of chlorophyll f, even in the presence of chlorophylls a and b, by PCP complexes shows the flexibility of chlorophyll-protein complexes and provides an opportunity for the introduction of new chlorophyll species to extend the photosynthetic spectral range.

Characterisation and Bioactivity Analysis of Peridinin-Chlorophyll a-Protein (PCP) Isolated from Symbiodinium tridacnidorum CS-73

Peridinin-Chlorophyll a-Proteins (PCP) are the major light harvesting proteins in photosynthetic dinoflagellates. PCP shows great variation in protein length, pigment ratio, sequence, and spectroscopic properties. PCP conjugates (PerCP) are widely used as fluorescent probes for cellular and tissue analysis in the biomedical field. PCP consists of a peridinin carotenoid; thereby, it can potentially be used as a bioactive compound in pharmaceutical applications. However, the biological activities of PCP are yet to be explored. In this study, we extracted, purified, and partially characterised the PCP from Symbiodinium tridacnidorum (CS-73) and explored its antioxidant, anti-cancer and anti-inflammation bioactivities. The PCP was purified using an ÄKTA™ PURE system and predicted to be of 17.3 kDa molecular weight (confirmed as a single band on SDS-PAGE) with an isoelectric point (pI) 5.6. LC-MS/MS and bioinformatic analysis of purified PCP digested with trypsin indicated it was 164 amino acids long with >90% sequence similarity to PCP of SymA3.s6014_g3 (belonging to clade A of Symbiodinium sp.) confirmed with 59 peptide combinations matched across its protein sequence. The spectroscopic properties of purified PCP showed a slight shift in absorption and emission spectra to previously documented analysis in Symbiodinium species possibly due to variation in amino acid sequences that interact with chl a and peridinin. Purified PCP consisted of a 19-amino-acid-long signal peptide at its N terminal and nine helixes in its secondary structure, with several protein binding sites and no DNA/RNA binding site. Furthermore, purified PCP exhibited antioxidant and in vitro anti-inflammation bioactivities, and anti-cancer activities against human metastatic breast adenocarcinoma (MDA-MB-231) and human colorectal (HTC-15) cancer cell lines. Together, all these findings present PCP as a promising candidate for continued investigations for pharmaceutical applications to cure chronic diseases, apart from its existing application as a fluorescent-probe.

Structural Tuning of Quantum Decoherence and Coherent Energy Transfer in Photosynthetic Light Harvesting

Photosynthetic organisms capture energy from solar photons by constructing light-harvesting proteins containing arrays of electronic chromophores. Collective excitations (excitons) arise when energy transfer between chromophores is coherent, or wavelike, in character. Here we demonstrate experimentally that coherent energy transfer to the lowest-energy excitons is principally controlled in a light-harvesting protein by the temporal persistence of quantum coherence rather than by the strength of vibronic coupling. In the peridinin-chlorophyll protein from marine dinoflagellates, broad-band two-dimensional electronic spectroscopy reveals that replacing the native chlorophyll a acceptor chromophores with chlorophyll b slows energy transfer from the carotenoid peridinin to chlorophyll despite narrowing the donor-acceptor energy gap. The formyl substituent on the chlorophyll b macrocycle hastens decoherence by sensing the surrounding electrostatic noise. These findings demonstrate how quantum coherence enhances the efficiency of energy transfer despite being very short lived in light-harvesting proteins at physiological temperatures.

Circadian and irradiance effects on expression of antenna protein genes and pigment contents in dinoflagellate Prorocentrum donghaiense (Dinophycae)

PCP and acpPC are the two major antennae proteins that bind pigments in peridinin-containing dinoflagellates. The relationship between antennae proteins and cellular pigments at molecular level is still poorly understood. Here we identified and characterized the two antennae protein genes in dinoflagellate Prorocentrum donghaiense under different light conditions. The mature PCP protein was 32 kDa, while acpPC was a polyprotein each of 19 kDa. Both genes showed higher expression under low light than under high light, suggesting their possible role in a low light adaptation mechanism. The two genes showed differential diel expression rhythm, with PCP being more highly expressed in the dark than in the light period and acpPC the other way around. HPLC analysis of cellular pigments indicated a diel change of chlorophyll c2, but invariability of other pigments. A stable peridinin: chlorophyll a pigment ratio was detected under different light intensities and over the diel cycle, although the diadinoxanthin:chlorophyll a ratio increased significantly with light intensity. The results suggest that 1) PCP and acpPC genes are functionally distinct, 2) PCP and acpPC can function under low light as an adaptive mechanism in P. donghaiense, 3). the ratios of diadinoxanthin:chlorophyll a and peridinin: chlorophyll a can potentially be used as an indicator of algal photophysiological status and a pigment signature respectively under different light conditions in P. donghaiense.

Distance measurements in peridinin-chlorophyll a-protein by light-induced PELDOR spectroscopy. Analysis of triplet state localization

Triplet-triplet energy transfer from chlorophylls to carotenoids is the mechanism underlying the photoprotective role played by carotenoids in many light harvesting complexes, during photosynthesis. The peridinin-chlorophyll-a protein (PCP) is a water-soluble light harvesting protein of the dinoflagellate Amphidinium carterae, employing peridinin as the main carotenoid to fulfil this function. The dipolar coupling of the triplet state of peridinin, populated under light excitation in isolated PCP, to the MTSSL nitroxide, introduced in the protein by site-directed mutagenesis followed by spin labeling, has been measured by Pulse ELectron-electron DOuble Resonance (PELDOR) spectroscopy. The triplet-nitroxide distance derived by this kind of experiments, performed for the first time in a protein system, allowed the assignment of the triplet state to a specific peridinin molecule belonging to the pigment cluster. The analysis strongly suggests that this peridinin is the one in close contact with the water ligand to the chlorophyll a, thus supporting previous evidences based on ENDOR and time resolved-EPR.

Vibrational relaxation as the driving force for wavelength conversion in the peridinin-chlorophyll a-protein

We present a computationally derived energy transfer model for the peridinin-chlorophyll a-protein (PCP), which invokes vibrational relaxation in the two lowest singlet excited states rather than internal conversion between them. The model allows an understanding of the photoinduced processes without assuming further electronic states or a dependence of the 2Ag state character on the vibrational sub-state. We report molecular dynamics simulations (CHARMM22 force field) and quantum mechanics/molecular mechanics (QM/MM) calculations on PCP. In the latter, the QM region containing a single peridinin (Per) chromophore or a Per-Chl a (chlorophyll a) pair is treated by density functional theory (DFT, CAM-B3LYP) for geometries and by DFT-based multireference configuration interaction (DFT/MRCI) for excitation energies. The calculations show that Per has a bright, green light absorbing 2Ag state, in addition to the blue light absorbing 1Bu state found in other carotenoids. Both states undergo a strong energy lowering upon relaxation, leading to emission in the red, while absorbing in the blue or green. The orientation of their transition dipole moments indicates that both states are capable of excited-state energy transfer to Chl a, without preference for either 1Bu or 2Ag as donor state. We propose that the commonly postulated partial intramolecular charge transfer (ICT) character of a donating Per state can be assigned to the relaxed 1Bu state, which takes on ICT character. By assuming that both 1Bu and 2Ag are able to donate to the Chl a Q band, one can explain why different chlorophyll species in PCP exhibit different acceptor capabilities.

The unique photophysical properties of the Peridinin-Chlorophyll-α-Protein

Peridinin-Chlorophyll-a-Proteins (PCPs) are water-soluble light harvesting complexes from dinoflagellates. They have unique light-harvesting and energy transfer properties which have been studied in details in the last 15 years. This review aims to give an overview on all the main aspects of PCPs photophysics, with an emphasis on some aspects which have not been reviewed in details so far, such as vibrational spectroscopy studies, theoretical calculations, and magnetic resonance studies. A paragraph on the present development of PCPs towards technological applications is also included.

Spectroscopic studies of plasmon coupling between photosynthetic complexes and metallic quantum dots

Metallic quantum dots, or nanoparticles, have found an increasing number of applications not only in nanotechnology and nanoscience, but also in neighboring disciplines, such as chemistry and biology. Among the variety of ways to exploit the unique properties of metallic nanostructures is the notion that plasmonic effects associated with the movement of free carriers in metallic nanoparticles may enhance photosynthetic function in naturally evolved organisms. We report on optical microscopy and spectroscopy studies of three hybrid nanostructures composed of spherical gold nanoparticles and peridinin-chlorophyll-protein (PCP), a light-harvesting complex from algae. In the case of a bioconjugated structure we find efficient, concentration dependent quenching due to non-radiative energy transfer. In contrast, for the PCP complexes deposited directly on Au nanoparticles, the emission is increased as a result of the strong increase of the fluorescence quantum yield. Finally, for a structure with controlled separation between metallic nanoparticles and the light-harvesting complexes the emission features non-monotonic behavior with maximum enhancement of about 6, which is due to a combination of fluorescence and absorption rate increases. In this way we demonstrate how the design of plasmonic hybrid nanostructures determines the optical response, which is important for engineering novel systems for photovoltaics and sensor applications, for instance.

Silica nanoparticles as a tool for fluorescence collection efficiency enhancement

In this work we demonstrate enhancement of the fluorescence collection efficiency for chlorophyll-containing photosynthetic complexes deposited on SiO2 spherical nanoparticles. Microscopic images of fluorescence emission reveal ring-like emission patterns associated with chlorophyll-containing complexes coupled to electromagnetic modes within the silica nanoparticles. The interaction leaves no effect upon the emission spectra of the complexes, and the transient behavior of the fluorescence also remains unchanged, which indicates no influence of the silica nanoparticles on the radiative properties of the fluorophores. We interpret this enhancement as a result of efficient scattering of electromagnetic field by the dielectric nanoparticles that increases collection efficiency of fluorescence emission.

Metal-enhanced fluorescence of chlorophylls in light-harvesting complexes coupled to silver nanowires

We investigate metal-enhanced fluorescence of peridinin-chlorophyll protein coupled to silver nanowires using optical microscopy combined with spectrally and time-resolved fluorescence techniques. In particular we study two different sample geometries: first, in which the light-harvesting complexes are deposited onto silver nanowires, and second, where solution of both nanostructures are mixed prior deposition on a substrate. The results indicate that for the peridinin-chlorophyll complexes placed in the vicinity of the silver nanowires we observe higher intensities of fluorescence emission as compared to the reference sample, where no nanowires are present. Enhancement factors estimated for the sample where the light-harvesting complexes are mixed together with the silver nanowires prior deposition on a substrate are generally larger in comparison to the other geometry of a hybrid nanostructure. While fluorescence spectra are identical both in terms of overall shape and maximum wavelength for peridinin-chlorophyll-protein complexes both isolated and coupled to metallic nanostructures, we conclude that interaction with plasmon excitations in the latter remains neutral to the functionality of the biological system. Fluorescence transients measured for the PCP complexes coupled to the silver nanowires indicate shortening of the fluorescence lifetime pointing towards modifications of radiative rate due to plasmonic interactions. Our results can be applied for developing ways to plasmonically control the light-harvesting capability of photosynthetic complexes.

The structure and function of eukaryotic photosystem I

Eukaryotic photosystem I consists of two functional moieties: the photosystem I core, harboring the components for the light-driven charge separation and the subsequent electron transfer, and the peripheral light-harvesting complex (LHCI). While the photosystem I-core remained highly conserved throughout the evolution, with the exception of the oxidizing side of photosystem I, the LHCI complex shows a high degree of variability in size, subunits composition and bound pigments, which is due to the large variety of different habitats photosynthetic organisms dwell in. Besides summarizing the most current knowledge on the photosystem I-core structure, we will discuss the composition and structure of the LHCI complex from different eukaryotic organisms, both from the red and the green clade. Furthermore, mechanistic insights into electron transfer between the donor and acceptor side of photosystem I and its soluble electron transfer carrier proteins will be given. This article is part of a Special Issue entitled: Regulation of Electron Transport in Chloroplasts.

Molecular factors controlling photosynthetic light harvesting by carotenoids

Carotenoids are naturally occurring pigments that absorb light in the spectral region in which the sun irradiates maximally. These molecules transfer this energy to chlorophylls, initiating the primary photochemical events of photosynthesis. Carotenoids also regulate the flow of energy within the photosynthetic apparatus and protect it from photoinduced damage caused by excess light absorption. To carry out these functions in nature, carotenoids are bound in discrete pigment-protein complexes in the proximity of chlorophylls. A few three-dimensional structures of these carotenoid complexes have been determined by X-ray crystallography. Thus, the stage is set for attempting to correlate the structural information with the spectroscopic properties of carotenoids to understand the molecular mechanism(s) of their function in photosynthetic systems. In this Account, we summarize current spectroscopic data describing the excited state energies and ultrafast dynamics of purified carotenoids in solution and bound in light-harvesting complexes from purple bacteria, marine algae, and green plants. Many of these complexes can be modified using mutagenesis or pigment exchange which facilitates the elucidation of correlations between structure and function. We describe the structural and electronic factors controlling the function of carotenoids as energy donors. We also discuss unresolved issues related to the nature of spectroscopically dark excited states, which could play a role in light harvesting. To illustrate the interplay between structural determinations and spectroscopic investigations that exemplifies work in the field, we describe the spectroscopic properties of four light-harvesting complexes whose structures have been determined to atomic resolution. The first, the LH2 complex from the purple bacterium Rhodopseudomonas acidophila, contains the carotenoid rhodopin glucoside. The second is the LHCII trimeric complex from higher plants which uses the carotenoids lutein, neoxanthin, and violaxanthin to transfer energy to chlorophyll. The third, the peridinin-chlorophyll-protein (PCP) from the dinoflagellate Amphidinium carterae, is the only known complex in which the bound carotenoid (peridinin) pigments outnumber the chlorophylls. The last is xanthorhodopsin from the eubacterium Salinibacter ruber. This complex contains the carotenoid salinixanthin, which transfers energy to a retinal chromophore. The carotenoids in these pigment-protein complexes transfer energy with high efficiency by optimizing both the distance and orientation of the carotenoid donor and chlorophyll acceptor molecules. Importantly, the versatility and robustness of carotenoids in these light-harvesting pigment-protein complexes have led to their incorporation in the design and synthesis of nanoscale antenna systems. In these bioinspired systems, researchers are seeking to improve the light capture and use of energy from the solar emission spectrum.

Identification of a single peridinin sensing Chl-a excitation in reconstituted PCP by crystallography and spectroscopy

The peridinin-chlorophyll a-protein (PCP) of dinoflagellates is unique among the large variety of natural photosynthetic light-harvesting systems. In contrast to other chlorophyll protein complexes, the soluble PCP is located in the thylakoid lumen, and the carotenoid pigments outnumber the chlorophylls. The structure of the PCP complex consists of two symmetric domains, each with a central chlorophyll a (Chl-a) surrounded by four peridinin molecules. The protein provides distinctive surroundings for the pigment molecules, and in PCP, the specific environment around each peridinin results in overlapping spectral line shapes, suggestive of different functions within the protein. One particular Per, Per-614, is hypothesized to show the strongest electronic interaction with the central Chl-a. We have performed an in vitro reconstitution of pigments into recombinant PCP apo-protein (RFPCP) and into a mutated protein with an altered environment near Per-614. Steady-state and transient optical spectroscopic experiments comparing the RFPCP complex with the reconstituted mutant protein identify specific amino acid-induced spectral shifts. The spectroscopic assignments are reinforced by a determination of the structures of both RFPCP and the mutant by x-ray crystallography to a resolution better than 1.5 A. RFPCP and mutated RFPCP are unique in representing crystal structures of in vitro reconstituted light-harvesting pigment-protein complexes.

Fluorescence spectroscopy of reconstituted peridinin-chlorophyll-protein complexes

Peridinin-chlorophyll-proteins (PCP) were reconstituted with binary 1:1 chlorophyll (Chl) mixtures of Chl a, Chl b, [3-acetyl]-Chl a (acChl a), and studied by bulk and single-molecule fluorescence spectroscopy. The latter provides a way to distinguish in a given sample hetero-chlorophyllous complexes that contain two different Chls from homo-chlorophyllous ones containing the same Chl in both binding sites. The results are compared with those of homo-chlorophyllous PCP reconstituted with pure Chl a, Chl b, or acChl a. Relative intensities of the Chl fluorescence in hetero-chlorophyllous complexes were obtained and modeled using the Förster description of energy transfer combined with known variations of peridinin (Per)-Chl excitation transfer rates for the different Chl pigments. In the case of hetero-chlorophyllous complexes containing acChl a, the energy transfer is unidirectional in the energetically preferable direction, while it is bi-directional in the sample reconstituted with Chl a and Chl b.

Relative binding affinities of chlorophylls in peridinin-chlorophyll-protein reconstituted with heterochlorophyllous mixtures

Peridinin-chlorophyll-protein (PCP), containing differently absorbing chlorophyll derivatives, are good models with which to study energy transfer among monomeric chlorophylls (Chls) by both bulk and single-molecule spectroscopy. They can be obtained by reconstituting the N-terminal domain of the protein (N-PCP) with peridinin and chlorophyll mixtures. Upon dimerization of these "half-mers", homo- and heterochlorophyllous complexes are generated, that correspond structurally to monomeric protomers of native PCP from Amphidinium carterae. Heterochlorophyllous complexes contain two different Chls in the two halves of the complete structure. Here, we report reconstitution of N-PCP with binary mixtures of Chl a, Chl b, and [3-acetyl]-Chl a. The ratios of the pigments were varied in the reconstitution mixture, and relative binding constants were determined from quantification of these pigments in the reconstituted PCPs. We find higher affinities for both Chl b and [3-acetyl]-Chl a than for the native pigment, Chl a.

Energy transfer in the peridinin-chlorophyll protein complex reconstituted with mixed chlorophyll sites

We use femtosecond transient absorption spectroscopy to study chlorophyll (Chl)-Chl energy transfer in the peridinin-chlorophyll protein (PCP) reconstituted with mixtures of either chlorophyll b (Chlb) and Chld or Chla and bacteriochlorophyll a (BChla). Analysis of absorption and transient absorption spectra demonstrated that reconstitution with chlorophyll mixtures produces a significant fraction of PCP complexes that contains a different Chl in each domain of the PCP monomer. The data also suggest that binding affinity of Chla is less than that of the other three Chl species. By exciting the Chl species lying at higher energy, we obtained energy transfer times of 40 +/- 5 ps (Chlb-Chld) and 59 +/- 3 ps (Chla-BChla). The experimental values match those obtained from the Förster equation, 36 and 50 ps, respectively, showing that energy transfer proceeds via the Förster mechanism. Excitation of peridinin in the PCP complex reconstituted with Chla/BChla mixture provided time constants of 2.6 and 0.4 ps for the peridinin-Chla and peridinin-BChla energy transfer, matching those obtained from studies of PCP complexes reconstituted with single chlorophyll species.

Energy transfer in reconstituted peridinin-chlorophyll-protein complexes: ensemble and single-molecule spectroscopy studies

We combine ensemble and single-molecule spectroscopy to gain insight into the energy transfer between chlorophylls (Chls) in peridinin-chlorophyll-protein (PCP) complexes reconstituted with Chl a, Chl b, as well as both Chl a and Chl b. The main focus is the heterochlorophyllous system (Chl a/b-N-PCP), and reference information essential to interpret experimental observations is obtained from homochlorophyllous complexes. Energy transfer between Chls in Chl a/b-N-PCP takes place from Chl b to Chl a and also from Chl a to Chl b with comparable Förster energy transfer rates of 0.0324 and 0.0215 ps(-1), respectively. Monte Carlo simulations yield the ratio of 39:61 for the excitation distribution between Chl a and Chl b, which is larger than the equilibrium distribution of 34:66. An average Chl a/Chl b fluorescence intensity ratio of 66:34 is measured, however, for single Chl a/b-N-PCP complexes excited into the peridinin (Per) absorption. This difference is attributed to almost three times more efficient energy transfer from Per to Chl a than to Chl b. The results indicate also that due to bilateral energy transfer, the Chl system equilibrates only partially during the excited state lifetimes.

Spectroscopy of the peridinin–chlorophyll-a protein: Insight into light-harvesting strategy of marine algae

An important component of the photosynthetic apparatus is a light-harvesting system that captures light energy and transfers it efficiently to the reaction center. Depending on environmental conditions, photosynthetic antennae have adopted various strategies for this function. Peridinin-chlorophyll-a protein (PCP) represents a unique situation because, unlike other antenna systems which have a preponderance of chlorophyll, it has the carotenoid, peridinin, as its major pigment. The key structural feature of peridinin is a conjugated carbonyl group. Owing to the presence of this group, an intramolecular charge-transfer excited state is formed in peridinin which exhibits different excited state spectra and dynamics depending on the polarity of the environment. The charge-transfer state also facilitates energy transfer between peridinin and chlorophyll-a in PCP. This review summarizes results of spectroscopic investigations of PCP in the past few years, emphasizing the specific light-harvesting strategy developed by marine photosynthetic organisms utilizing carbonyl-containing carotenoids in their antenna complexes.

Optical spectroscopic studies of light-harvesting by pigment-reconstituted peridinin-chlorophyll-proteins at cryogenic temperatures

Low temperature, steady-state, optical spectroscopic methods were used to study the spectral features of peridinin-chlorophyll-protein (PCP) complexes in which recombinant apoprotein has been refolded in the presence of peridinin and either chlorophyll a (Chl a), chlorophyll b (Chl b), chlorophyll d (Chl d), 3-acetyl-chlorophyll a (3-acetyl-Chl a) or bacteriochlorophyll a (BChl a). Absorption spectra taken at 10 K provide better resolution of the spectroscopic bands than seen at room temperature and reveal specific pigment-protein interactions responsible for the positions of the Qy bands of the chlorophylls. The study reveals that the functional groups attached to Ring I of the two protein-bound chlorophylls modulate the Qy and Soret transition energies. Fluorescence excitation spectra were used to compute energy transfer efficiencies of the various complexes at room temperature and these were correlated with previously reported ultrafast, time-resolved optical spectroscopic dynamics data. The results illustrate the robust nature and value of the PCP complex, which maintains a high efficiency of antenna function even in the presence of non-native chlorophyll species, as an effective tool for elucidating the molecular details of photosynthetic light-harvesting.

Peridinin-chlorophyll-protein reconstituted with chlorophyll mixtures: Preparation, bulk and single molecule spectroscopy

Reconstitution of the 16 kDa N-terminal domain of the peridinin-chlorophyll-protein, N-PCP, with mixtures of chlorophyll a (Chl a) and Chl b, resulted in 32 kDa complexes containing two pigment clusters, each bound to one N-PCP. Besides homo-chlorophyllous complexes, hetero-chlorophyllous ones were obtained that contain Chl a in one pigment cluster, and Chl b in the other. Binding of Chl b is stronger than that of the native pigment, Chl a. Energy transfer from Chl b to Chl a is efficient, but there are only weak interactions between the two pigments. Individual homo- and hetero-chlorophyllous complexes were investigated by single molecule spectroscopy using excitation into the peridinin absorption band and scanning of the Chl fluorescence, the latter show frequently well resolved emissions of the two pigments.

Tuning energy transfer in the peridinin-chlorophyll complex by reconstitution with different chlorophylls

In vitro studies of the carotenoid peridinin, which is the primary pigment from the peridinin chlorophyll-a protein (PCP) light harvesting complex, showed a strong dependence on the lifetime of the peridinin lowest singlet excited state on solvent polarity. This dependence was attributed to the presence of an intramolecular charge transfer (ICT) state in the peridinin excited state manifold. The ICT state was also suggested to be a crucial factor in efficient peridinin to Chl-a energy transfer in the PCP complex. Here we extend our studies of peridinin dynamics to reconstituted PCP complexes, in which Chl-a was replaced by different chlorophyll species (Chl-b, acetyl Chl-a, Chl-d and BChl-a). Reconstitution of PCP with different Chl species maintains the energy transfer pathways within the complex, but the efficiency depends on the chlorophyll species. In the native PCP complex, the peridinin S1/ICT state has a lifetime of 2.7 ps, whereas in reconstituted PCP complexes it is 5.9 ps (Chl-b) 2.9 ps (Chl-a), 2.2 ps (acetyl Chl-a), 1.9 ps (Chl-d), and 0.45 ps (BChl-a). Calculation of energy transfer rates using the Förster equation explains the differences in energy transfer efficiency in terms of changing spectral overlap between the peridinin emission and the absorption spectrum of the acceptor. It is proposed that the lowest excited state of peridinin is a strongly coupled S1/ICT state, which is the energy donor for the major energy transfer channel. The significant ICT character of the S1/ICT state in PCP enhances the transition dipole moment of the S1/ICT state, facilitating energy transfer to chlorophyll via the Förster mechanism. In addition to energy transfer via the S1/ICT, there is also energy transfer via the S2 and hot S1/ICT states to chlorophyll in all reconstituted PCP complexes.