Molecular topology of the photosynthetic light-harvesting pigment complex, peridinin-chlorophyll a-protein, from marine dinoflagellates

Abstract

The photosynthetic light-harvesting complex, peridinin-chlorophyll a-protein, was isolated from several marine dinoflagellates including Glenodinium sp. by Sephadex and ion-exchange chromatography. The carotenoid (peridinin)-chlorophyll a ratio in the complex is estimated to be 4:1. The fluorescence excitation spectrum of the complex indicates that energy absorbed by the carotenoid is transferred to the chlorophyll a molecule with 100% efficiency. Fluorescence lifetime measurements indicate that the energy transfer is much faster than fluorescence emission from chlorophyll a. The four peridinin molecules within the complex appear to form two allowed exciton bands which split the main absorption band of the carotenoid into two circular dichronic bands (with negative ellipticity band at 538 nm and positive band at 463 nm in the case of peridinin-chlorophyl a-protein complex from Glenodinium sp.). The fluorescence polarization of chlorophyll a in the complex at 200 K is about 0.1 in both circular dichroic excitation bands of the carotenoid chromophore. From these circular dichroic and fluorescence polarization data, a possible molecular arrangement of the four peridinin and chlorophyll molecules has been deduced for the complex. The structure of the complex deduced is also consistent with the magnitude of the exciton spliting (ca. greater than 3000 cm-1) at the intermolecular distance in the dimer pair of peridinin (ca. 12 A). This structural feature accounts for the efficient light-harvesting process of dinoflagellates as the exciton interaction lengthens the lifetime of peridinin (radiative) and the complex topology increases the energy transfer probability. The complex is, therefore, a useful molecular model for elucidating the mechanism and efficiency of solar energy conversion in vivo as well as in vitro.

The Green Fluorescent Protein

“…Several other bioluminescent species also have emission-shifting accessory proteins, but so far the chromophores all seem to be external cofactors such as lumazines (15) or flavins (16), which diminish their attractiveness as biotechnological tags and probes. Likewise phycobiliproteins (17) and peridinin-chlorophyll-a protein (18), which are highly fluorescent and attractively long-wavelength accessory pigments in photosynthesis, use tetrapyrrole cofactors as their pigments. Correct insertion of the cofactors into the apoproteins has not been demonstrated in foreign organisms, so these proteins are not ready to compete with Aequorea GFP.…”

Structural Basis of Light Harvesting by Carotenoids: Peridinin-Chlorophyll-Protein from Amphidinium carterae

“…In PCP fro tU Amphidinium carterae, the NH 2 -and COOH-tenuinal dotuains (6) of th.e cDNAderived sequence (30.2 kD) share 56% of their residues, and each donlain binds a cluster of one chlorophyll a and four peridinin tuolecules. Within each cluster, the efficiency of singlet energy transfer fr01n peridinin to chlorophyll is close to unity (7). Models of chromophore interaction within and atuong the clusters have previously been based on spectroscopic investigations (7,8).…”

“…Within each cluster, the efficiency of singlet energy transfer fr01n peridinin to chlorophyll is close to unity (7). Models of chromophore interaction within and atuong the clusters have previously been based on spectroscopic investigations (7,8). Structural infornlation, such as that available for 1uenl-brane-bound LHCs fron1 higher plants (3) and bacteria (9), has greatly enhanced our understanding of antenna systen1s having chlorophyll as the n1ain pignlent.…”

An Approach Based on Synthetic Organic Chemistry Toward Elucidation of Highly Efficient Energy Transfer Ability of Peridinin in Photosynthesis

“…Each of the polypeptides binds eight peridinin molecules and two Chl a molecules, and the allene function of peridinin exsists in the center of the PCP. In this complex, a so-called antenna pigment, peridinin exhibits exceptionally high (> 95%) energy transfer efficiencies to Chl a (Song et al, 1976;Mimuro et al, 1993). This energy transfer efficiency is thought to be related to the unique structure of peridinin, which possesses allene and ylidenebutenolide functions and the unusual C37 carbon skeleton referred to as a 'nor-carotenoid' (Fig.…”