Molecular structures reveal the origin of spectral variation in cryptophyte light harvesting antenna proteins.

In addition to their membrane-bound chlorophyll a/c light-harvesting antenna, the cryptophyte algae have evolved a unique phycobiliprotein antenna system located in the thylakoid lumen. The basic unit of this antenna consists of two copies of an αβ protomer where the α and β subunits scaffold different combinations of a limited number of linear tetrapyrrole chromophores. While the β subunit is highly conserved, encoded by a single plastid gene, the nuclear-encoded α subunits have evolved diversified multigene families.

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.

Consistent Model of Ultrafast Energy Transfer in Peridinin Chlorophyll- Protein Using Two-Dimensional Electronic Spectroscopy and Förster Theory.

Solar light harvesting begins with electronic energy transfer in structurally complex light-harvesting antennae such as the peridinin chlorophyll- protein from dinoflagellate algae. Peridinin chlorophyll- protein is composed of a unique combination of chlorophylls sensitized by carotenoids in a 4:1 ratio, and ultrafast spectroscopic methods have previously been utilized in elucidating their energy-transfer pathways and timescales. However, due to overlapping signals from various chromophores and competing pathways and timescales, a consistent model of intraprotein electronic energy transfer has been elusive.

Femtosecond transient infrared and stimulated Raman spectroscopy shed light on the relaxation mechanisms of photo-excited peridinin.

By means of one- and two-dimensional transient infrared spectroscopy and femtosecond stimulated Raman spectroscopy, we investigated the excited state dynamics of peridinin, a carbonyl carotenoid occurring in natural light harvesting complexes. The presence of singly and doubly excited states, as well as of an intramolecular charge transfer (ICT) state, makes the behavior of carbonyl carotenoids in the excited state very complex. In this work, we investigated by time resolved spectroscopy the relaxation of photo-excited peridinin in solvents of different polarities and as a function of the excitation wavelength.

Pigment organisation in the membrane-intrinsic major light-harvesting complex of Amphidinium carterae: Structural characterisation of the peridinins and chlorophylls a and c2 by resonance Raman spectroscopy and from sequence analysis.

The structures and environments of the protein-bound peridinins (Pers) and chlorophylls (Chls) a/c2 in the membrane-intrinsic major light-harvesting complex of the dinoflagellate Amphidinium carterae (LHCAmph) are characterised using resonance Raman (RR) spectroscopy with 11 excitation wavelengths, at 77K. The excitation-dependent variation in the CC stretching mode (ν1) suggests the presence of three Pers with conjugation lengths over 8 double bonds (dBs), and one diadinoxanthin, between 413.7 and 528.

Single-residue insertion switches the quaternary structure and exciton states of cryptophyte light-harvesting proteins.

Observation of coherent oscillations in the 2D electronic spectra (2D ES) of photosynthetic proteins has led researchers to ask whether nontrivial quantum phenomena are biologically significant. Coherent oscillations have been reported for the soluble light-harvesting phycobiliprotein (PBP) antenna isolated from cryptophyte algae. To probe the link between spectral properties and protein structure, we determined crystal structures of three PBP light-harvesting complexes isolated from different species.

Conservation of spin polarization during triplet-triplet energy transfer in reconstituted peridinin-chlorophyll-protein complexes.

Peridinin-chlorophyll-protein (PCP) complexes, where the N-terminal domain of native PCP from Amphidinium carterae has been reconstituted with different chlorophyll (Chl) species, have been investigated by time-resolved EPR in order to elucidate the details of the triplet-triplet energy transfer (TTET) mechanism. This spectroscopic approach exploits the concept of spin conservation during TTET, which leads to recognizable spin-polarization effects in the observed time-resolved EPR spectra. The spin polarization produced at the acceptor site (peridinin) depends on the initial polarization of the donor (chlorophyll) and on the relative geometric arrangement of the donor-acceptor spin axes.

Triplet-triplet energy transfer in the major intrinsic light-harvesting complex of Amphidinium carterae as revealed by ODMR and EPR spectroscopies.

We present an optically detected magnetic resonance (ODMR) and electron paramagnetic resonance (EPR) spectroscopic study on the quenching of photo-induced chlorophyll triplet states by carotenoids, in the intrinsic light-harvesting complex (LHC) from the dinoflagellate Amphidinium carterae. Two carotenoid triplet states, differing in terms of optical and magnetic spectroscopic properties, have been identified and assigned to peridinins located in different protein environment. The results reveal a parallelism with the triplet-triplet energy transfer (TTET) process involving chlorophyll a and luteins observed in the LHC-II complex of higher plants.

Identification of excited-state energy transfer and relaxation pathways in the peridinin-chlorophyll complex: an ultrafast mid-infrared study.

The peridinin chlorophyll-a protein (PCP) is a water-soluble, trimeric light harvesting complex found in marine dinoflagellates that binds peridinin and Chl-a in an unusual stoichiometric ratio of 4:1. In this paper, the pathways of excited-state energy transfer and relaxation in PCP were identified by means of femtosecond visible-pump, mid-infrared probe spectroscopy. In addition, excited-state relaxation of peridinin dissolved in organic solvent (CHCl(3) and MeOH) was investigated.

X-ray structures of the peridinin-chlorophyll-protein reconstituted with different chlorophylls.

The peridinin-chlorophyll a-protein (PCP) from dinoflagellates is a soluble light harvesting antenna which gathers incoming photons mainly by the carotenoid peridinin. In PCPs reconstituted with different chlorophylls, the peridinin to chlorophyll energy transfer rates are well predicted by a Förster-like theory, but only if the pigment arrangements are identical in all PCPs. We have determined the X-ray structures of PCPs reconstituted with Chlorophyll-b (Chl-b), Chlorophyll-d (Chl-d) and Bacteriochlorophyll-a (BChl-a) to resolutions View Article and Find Full Text PDF

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.

X-ray structure of the high-salt form of the peridinin-chlorophyll a-protein from the dinoflagellate Amphidinium carterae: modulation of the spectral properties of pigments by the protein environment.

Light-harvesting complexes have evolved into very different structures but fulfill the same function, efficient harvesting of solar energy. In these complexes, pigments are fine-tuned and properly arranged to gather incoming photons. In the photosynthetic dinoflagellate Amphidinium carterae, two variants of the soluble light-harvesting complex PCP have been found [main form PCP (MFPCP) and high-salt PCP (HSPCP)], which show small variations in their pigment arrangement and tuning mechanisms.

Triplet-triplet energy transfer in Peridinin-Chlorophyll a-protein reconstituted with Chl a and Chl d as revealed by optically detected magnetic resonance and pulse EPR: comparison with the native PCP complex from Amphidinium carterae.

The triplet state of the carotenoid peridinin, populated by triplet-triplet energy transfer from photoexcited chlorophyll triplet state, in the reconstituted Peridinin-Chlorophyll a-protein, has been investigated by ODMR (Optically detected magnetic resonance), and pulse EPR spectroscopies. The properties of peridinins associated with the triplet state formation in complexes reconstituted with Chl a and Chl d have been compared to those of the main-form peridinin-chlorophyll protein (MFPCP) isolated from Amphidinium carterae. In the reconstituted samples no signals due to the presence of chlorophyll triplet states have been detected, during either steady state illumination or laser-pulse excitation.

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.

Transcript analysis of dinoflagellate plastid gene minicircles.

The dinoflagellate chloroplast genome is fragmented into a number of plasmid-like minicircles, mostly containing one or more genes, and with a conserved core. We show here that, in addition to the transcripts of similar sizes to individual genes that have been reported previously, there are larger transcripts beginning and ending close to the core region. These may give rise to the smaller transcripts by processing.

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.

Triplet state dynamics in peridinin-chlorophyll-a-protein: a new pathway of photoprotection in LHCs?

This work investigates the interaction of carotenoid and chlorophyll triplet states in the peridinin-chlorophyll-a-protein (PCP) of Amphidinium carterae using step-scan Fourier transform infrared spectroscopy. We identify two carotenoid triplet state lifetimes of approximately 13 and approximately 42 mus in the spectral region between 1800 and 1100 cm(-1) after excitation of the 'blue' and 'red' peridinin (Per) conformers and the Q(y) of chlorophyll-a (Chl-a). The fast and slow decaying triplets exhibit different spectral signatures in the carbonyl region.

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.

Comparative analysis of dinoflagellate chloroplast genomes reveals rRNA and tRNA genes.

Background: Peridinin-containing dinoflagellates have a highly reduced chloroplast genome, which is unlike that found in other chloroplast containing organisms. Genome reduction appears to be the result of extensive transfer of genes to the nuclear genome. Unusually the genes believed to be remaining in the chloroplast genome are found on small DNA 'minicircles'.

Femtosecond time-resolved absorption spectroscopy of main-form and high-salt peridinin-chlorophyll a-proteins at low temperatures.

Steady-state and femtosecond time-resolved optical methods have been used to compare the spectroscopic features and energy transfer dynamics of two systematically different light-harvesting complexes from the dinoflagellate Amphidinium carterae: main-form (MFPCP) and high-salt (HSPCP) peridinin-chlorophyll a-proteins. Pigment analysis and X-ray diffraction structure determinations [Hofmann, E., Wrench, P.

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 charge-transfer character of the S0 --> S2 transition in the carotenoid peridinin is revealed by Stark spectroscopy.

Peridinin, the carotenoid in the peridinin chlorophyll a protein (PCP), was studied by Stark (electroabsorption) spectroscopy to determine the change in electrostatic properties produced on excitation within the absorption band, in methyl tetrahydrofuran (MeTHF) versus ethylene glycol (EG), at 77 K. Strikingly, a large change in the permanent dipole moment (|Deltamu|) was found between the ground state, S(0) (1(1)A(g)(-)), and the Franck-Condon region of the S(2) (1(1)B(u)(+)) excited state, in both MeTHF (22 D) and EG (approximately 27 D), thus revealing the previously unknown charge transfer (CT) character of this pi-pi transition in peridinin. Such a large |Deltamu| produced on excitation, we suggest, facilitates the bending of the lactone moiety, toward which charge transfer occurs, and the subsequent formation of the previously identified intramolecular CT (ICT) state at lower energy.

Energy transfer in the major intrinsic light-harvesting complex from Amphidinium carterae.

Carbonyl carotenoids are important constituents of the antenna complexes of marine organisms. These carotenoids possess an excited state with a charge-transfer character (intramolecular charge transfer state, ICT), but many details of the carotenoid to chlorophyll energy transfer mechanisms are as yet poorly understood. Here, we employ femtosecond transient absorption spectroscopy to study energy transfer pathways in the intrinsic light-harvesting complex (LHC) of dinoflagellates, which contains the carbonyl carotenoid peridinin.

Use of ultrafast dispersed pump-dump-probe and pump-repump-probe spectroscopies to explore the light-induced dynamics of peridinin in solution.

Optical pump-induced dynamics of the highly asymmetric carotenoid peridinin in methanol was studied by dispersed pump-probe, pump-dump-probe, and pump-repump-probe transient absorption spectroscopy in the visible region. Dispersed pump-probe measurements show that the decay of the initially excited S2 state populates two excited states, the S1 and the intramolecular charge-transfer (ICT) state, at a ratio determined by the excitation wavelength. The ensuing spectral evolution occurs on the time scale of a few picoseconds and suggests the equilibration of these states.