Peridinin-chlorophyll A-protein Complex Research Articles

Unveiling the excited state energy transfer pathways in peridinin-chlorophyll a-protein by ultrafast multi-pulse transient absorption spectroscopy

Time-resolved multi-pulse methods were applied to investigate the excited state dynamics, the interstate couplings, and the excited state energy transfer pathways between the light-harvesting pigments in peridinin-chlorophyll a-protein (PCP). The utilized pump-dump-probe techniques are based on perturbation of the regular PCP energy transfer pathway. The PCP complexes were initially excited with an ultrashort pulse, resonant to the S0→S2 transition of the carotenoid peridinin. A portion of the peridinin-based emissive intramolecular charge transfer (ICT) state was then depopulated by applying an ultrashort NIR pulse that perturbed the interaction between S1 and ICT states and the energy flow from the carotenoids to the chlorophylls. The presented data indicate that the peridinin S1 and ICT states are spectrally distinct and coexist in an excited state equilibrium in the PCP complex. Moreover, numeric analysis of the experimental data asserts ICT→Chl-a as the main energy transfer pathway in the photoexcited PCP systems.

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.

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.

Energy transfer pathways in the peridinin chlorophyll-a protein complex as revealed by the near-infrared time-resolved spectroscopy

In vitro studies of the primary pigment peridinin from peridinin chlorophyll-a protein (PCP) light harvesting complex showed a strong dependence of the lifetime of peridinin lowest singlet excited state on solvent polarity as well as appearance of a stimulated emission (SE) band in the near-IR range of the transient absorption spectrum in the polar solvent methanol. Both the lifetime dependence and the SE band were attributed to the presence of a new state with charge transfer (CT) character. The aim of this study was to investigate dynamics within the PCP using near-IR femtosecond pump-probe spectroscopy. Kinetics obtained in our measurements reveal that the lowest singlet state of peridinin in the PCP complex has a lifetime of 2.1 ? 2.5 ps. Here, we used the transient absorption in near-IR region, which is almost free from contributions from other pigments and represents absorption signal from the lowest singlet excited state to the S2 state of peridinin. Measurements of the near-IR transient absorption spectra showed that the SE band observed earlier for peridinin in methanol is also clearly present for peridinin in PCP. Kinetics measured across the SE band exhibit the same dynamics as kinetics measured at spectral regions corresponding to absorption from the lowest singlet excited state of the peridinin as well as to the bleaching of the chlorophyll-a band. These results suggest that the CT state is directly involved in the energy transfer process within PCP light harvesting complex.

Time-course of photoadaptation in the symbiotic sea anemone Anemonia viridis

The time-course of photoadaptation in the symbiotic sea anemone Anemonia viridis (Forskal) was determined on freshly collected anemones which were maintained under low light (LL: 10 μE m-2s-1) or high light (HL: 300 μE m-2s-1) over a period of 35 d. Photosynthesis versus irradiance curves (P vs I) normalised to anemone dry weight were determined for anemones at the start of the experiment and for both groups at 7 d intervals. Photosynthetic parameters derived from the P vs I curves, P max gross (the maximum photosynthetic capacity of the zooxanthellae), α (an estimate of photosynthetic efficiency) and I k(the light-saturating irradiance), and the respiration rate, showed that anemones were high-light adapted before the experiment began. Thereafter, any observed changes occurred only in anemones adapting to the low-light regime. P max gross remained relatively constant over 35 d and there was no significant difference between LL and HL groups. In the LL group α increased and both I kand the respiration rate decreased significantly. These photoadaptive responses were most rapid in the first 7 d, after which change was gradual until about Day 28, when photoadaptation appeared to be complete. In order to predict the physiological mechanisms of photoadaptation to low light, P gross vs I curves normalised to zooxanthellae biomass were constructed for LL and HL anemones at 35 d. Zooxanthellae density and photosynthetic pigment content were also analysed. For LL-adapted anemones, α and chlorophyll a were higher, there were no differences in algal density and chlorophyll c 2 and I kwas lower. It is proposed that the size of the peridinin-chlorophyll a-protein complex (PCP) of the light-harvesting complex was increased to facilitate photoadaptation. Plotting P net vs I normalised to anemone dry weight on the 35 d-photoadapted anemones gave a measure of changes in the excess photosynthetically fixed carbon that was potentially available to the host. Net photosynthesis of the LL group was higher at subsaturating light intensities as a result of the increase in α, and at saturating light intensities P max net was higher as a result of a decrease in the rate of respiration of the whole symbiotic association.

気仙沼湾に発生した赤変カキについて

The pigment of the brick-red colored oysters collected in the Kesennuma Bay was identified as peridinin. Peridinin existed in the form of water soluble peridinin-chlorophyll a-protein complex (PCP) in the digestive diverticulum. The properties of this PCP were as follows: λmax: 410, 480, 670nm; chromogen (peridinin: chl. a=4:1 molar ratio); coagulation temperature 40-60°C; ammonium sulfate precipitation 60-80% saturation. Polyacrylamide disc gel electrophoresis showed a single broad brick-red band. Sephadex G-100 gel filtration gave two components: F II. The properties of PCPs suggest that the PCPs in oysters are derved from the PCP of the red tide dinoflagellate Prorocentrum micans.

Occurrence of peridinin-chlorophyll a-protein complex in red tide dinoflagellate Prorocentrum micans.

Peridinin-chlorophyll a-protein complex was isolated and partially purified from P. micans. The PCP had a molar ratio of peridinin: chlorophyll a=4:1 MW was 37, 000. pI values were 8.3, 7.9, 5.2. λmax values were 440, 480, 670nm.

Purification and characterization of peridinin-chlorophyll a-proteins from the marine dinoflagellates Glenodinium sp. and Gonyaulax polyedra

A peridinin-chlorophyll a-protein complex (PCP) was obtained in large quantity from the marine dinoflagellates, Glenodinium sp. and Gonyaulax polyedra. The chromoproteins have similar molecular weights, 35,500 for Glenodinium sp. and 34,500 for G. polyedra. The proteins from the PCP complex of Glenodinium sp. dissociated from the chromophore on treatment with 1% sodium dodecyl sulfate (SDS) at room temperature. The protein component was a single subunit with a molecular weight of 15,500. Proteins from the PCP complex of G. polyedra were composed of a single polypeptide with a molecular weight of about 32,000. Two peridinin-chlorophyll a-proteins from Glenodinium sp. accounted for 70% of the PCP complex and had isoelectric points of 7.4 and 7.3. The PCP complex from G. polyedra was dominated by a single chromoprotein with an isoelectric point of 7.2 Chromophore analysis indicated the presence of only peridinin and chlorophyll a in a molar ratio approaching 4:1. Other pigments characteristically found in dinoflagellates were absent. Fluorescence excitation spectra of purified PCP indicated an efficient energy transfer from peridinin to chlorophyll a, an observation that lends support to the reported role of peridinin as an accessory pigment in photosynthetic oxygen evolution. In several other brown colored dinoflagellates examined, PCP representtd less than 20% of the total peridinin. However, no PCP could be isolated from cultures of Amphidinium carterae (PY-1). This study provides further evidence that PCP is a normal component of most peridinin-containing dinoflagellates, and functions as a light-harvesting component of the dinoflagellate chloroplast. No fucoxanthin-containing analog of PCP was detected in the chrysophyte, Cricosphera carterae and the dinoflagellate Glenodinium foliaceum.