The photosynthetic apparatus of higher plants can dissipate excess excitation energy during high light exposure, by deactivating excited chlorophylls through a mechanism called nonphotochemical quenching (NPQ). However, the precise molecular details of quenching and the mechanism regulating the quenching level are still not completely understood. Focusing on the major light-harvesting complex LHCII of Photosystem II, we show that a charge transfer state involving Lutein can efficiently quench chlorophyll excitation, and reduce the excitation lifetime of LHCII to the levels measured in the deeply quenched LHCII aggregates. Through a combination of molecular dynamics simulations, multiscale quantum chemical calculations, and kinetic modeling, we demonstrate that the quenching level can be finely tuned by the protein, by regulating the energy of the charge transfer state. Our results suggest that a limited conformational rearrangement of the protein scaffold could act as a molecular switch to activate or deactivate the quenching mechanism.

译文

高等植物的光合装置可以通过一种称为非光化学猝灭 (NPQ) 的机制使激发的叶绿素失活,从而在高光照射期间消散多余的激发能量。然而,淬火的精确分子细节和调节淬火水平的机理仍不完全清楚。着眼于光系统II的主要集光复合物LHCII,我们表明,涉及叶黄素的电荷转移状态可以有效地抑制叶绿素激发,并将LHCII的激发寿命降低到深度淬灭的LHCII聚集体中测得的水平。通过分子动力学模拟,多尺度量子化学计算和动力学建模的组合,我们证明了通过调节电荷转移状态的能量,蛋白质可以微调猝灭水平。我们的结果表明,蛋白质支架的有限构象重排可以充当分子开关,以激活或停用猝灭机制。

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