Structure-Based Calculations of Optical Spectra of Photosystem I Suggest an Asymmetric Light-Harvesting Process

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• 作者：Julian Adolphs ; Frank Mh ; Mohamed El-Amine Madjet ; Marcel Schmidt am Busch ; Thomas Renger
• 刊名：Journal of the American Chemical Society
• 出版年：2010
• 出版时间：March 17, 2010
• 年：2010
• 卷：132
• 期：10
• 页码：3331-3343
• 全文大小：520K
• 年卷期：v.132,no.10(March 17, 2010)
• ISSN：1520-5126

文摘

Optical line shape theory is combined with a quantum-chemical/electrostatic calculation of the site energies of the 96 chlorophyll a pigments and their excitonic couplings to simulate optical spectra of photosystem I core complexes from Thermosynechococcus elongatus. The absorbance, linear dichroism and circular dichroism spectra, calculated on the basis of the 2.5 Å crystal structure, match the experimental data semiquantitatively allowing for a detailed analysis of the pigment−protein interaction. The majority of site energies are determined by multiple interactions with a large number (>20) of amino acid residues, a result which demonstrates the importance of long-range electrostatic interactions. The low-energy exciton states of the antenna are found to be located at a nearest distance of about 25 Å from the special pair of the reaction center. The intermediate pigments form a high-energy bridge, the site energies of which are stabilized by a particularly large number (>100) of amino acid residues. The concentration of low energy exciton states in the antenna is larger on the side of the A-branch of the reaction center, implying an asymmetric delivery of excitation energy to the latter. This asymmetry in light-harvesting may provide the key for understanding the asymmetric use of the two branches in primary electron transfer reactions. Experiments are suggested to check for this possibility.