Novoderezhkin Vladimir I, Palacios Miguel A, van Amerongen Herbert, van Grondelle Rienk
A. N. Belozersky Institute of Physico-Chemical Biology, Moscow State University, Leninskie Gory, 119992 Moscow, Russia.
J Phys Chem B. 2005 May 26;109(20):10493-504. doi: 10.1021/jp044082f.
We have modeled steady-state spectra and energy-transfer dynamics in the peripheral plant light-harvesting complex LHCII using new structural data. The dynamics of the chlorophyll (Chl) b-->Chl a transfer and decay of selectively excited "bottleneck" Chl a and b states have been studied by femtosecond pump-probe spectroscopy. We propose an exciton model of the LHCII trimer (with specific site energies) which allows a simultaneous quantitative fit of the absorption, linear-dichroism, steady-state fluorescence spectra, and transient absorption kinetics upon excitation at different wavelengths. In the modeling we use the experimental exciton-phonon spectral density and modified Redfield theory. We have found that fast b-->a transfer is determined by a good connection of the Chls b to strongly coupled Chl a clusters, i.e., a610-a611-a612 trimer and a602-a603 and a613-a614 dimers. Long-lived components of the energy-transfer kinetics are determined by a quick population of red-shifted Chl b605 and blue-shifted Chl a604 followed by a very slow (3 ps for b605 and 12 ps for a604) flow of energy from these monomeric bottleneck sites to the Chl a clusters. The dynamics within the Chl a region is determined by fast (with time constants down to sub-100 fs) exciton relaxation within the a610-a611-a612 trimer, slower 200-300 fs relaxation within the a602-a603 and a613-a614 dimers, even slower 300-800 fs migration between these clusters, and very slow transfer from a604 to the quasi-equilibrated a sites. The final equilibrium is characterized by predominant population of the a610-a611-a612 cluster (mostly the a610 site). The location of this cluster on the outer side of the LHCII trimer probably provides a good connection with the other subunits of PSII.
我们利用新的结构数据，对植物外周光捕获复合物LHCII中的稳态光谱和能量转移动力学进行了建模。通过飞秒泵浦-探测光谱研究了叶绿素（Chl）b向Chl a的转移动力学以及选择性激发的“瓶颈”Chl a和b态的衰减。我们提出了一个LHCII三聚体的激子模型（具有特定的位点能量），该模型能够同时定量拟合在不同波长激发下的吸收光谱、线性二色性光谱、稳态荧光光谱以及瞬态吸收动力学。在建模过程中，我们使用了实验激子-声子光谱密度和修正的Redfield理论。我们发现，快速的b向a转移是由Chl b与强耦合的Chl a簇（即a610-a611-a612三聚体以及a602-a603和a613-a614二聚体）的良好连接所决定的。能量转移动力学的长寿命成分是由红移的Chl b605和蓝移的Chl a604的快速填充所决定的，随后能量从这些单体瓶颈位点向Chl a簇的流动非常缓慢（b605为3皮秒，a604为12皮秒）。Chl a区域内的动力学由a610-a611-a612三聚体内快速（时间常数低至100飞秒以下）的激子弛豫、a602-a603和a613-a614二聚体内较慢的200-300飞秒弛豫、这些簇之间更慢的300-800飞秒迁移以及从a604到准平衡a位点的非常缓慢的转移所决定。最终的平衡状态以a610-a611-a612簇（主要是a610位点）的占主导地位的填充为特征。该簇在LHCII三聚体外侧的位置可能为与PSII的其他亚基提供了良好的连接。
