Dipartimento di Chimica e Chimica Industriale, University of Pisa, via G. Moruzzi 13, 56124, Pisa, Italy.
Department of Chemistry, University College London, WC1E 6BT, London, UK.
Nat Commun. 2021 Dec 9;12(1):7152. doi: 10.1038/s41467-021-27526-8.
Light-harvesting complexes of plants exert a dual function of light-harvesting (LH) and photoprotection through processes collectively called nonphotochemical quenching (NPQ). While LH processes are relatively well characterized, those involved in NPQ are less understood. Here, we characterize the quenching mechanisms of CP29, a minor LHC of plants, through the integration of two complementary enhanced-sampling techniques, dimensionality reduction schemes, electronic calculations and the analysis of cryo-EM data in the light of the predicted conformational ensemble. Our study reveals that the switch between LH and quenching state is more complex than previously thought. Several conformations of the lumenal side of the protein occur and differently affect the pigments' relative geometries and interactions. Moreover, we show that a quenching mechanism localized on a single chlorophyll-carotenoid pair is not sufficient but many chlorophylls are simultaneously involved. In such a diffuse mechanism, short-range interactions between each carotenoid and different chlorophylls combined with a protein-mediated tuning of the carotenoid excitation energies have to be considered in addition to the commonly suggested Coulomb interactions.
植物的光捕获复合物通过被统称为非光化学猝灭（NPQ）的过程发挥光捕获（LH）和光保护的双重功能。虽然 LH 过程相对较好地被描述，但 NPQ 涉及的过程则理解较少。在这里，我们通过整合两种互补的增强采样技术、降维方案、电子计算以及根据预测的构象集合分析低温电子显微镜数据，来描述 CP29（植物的一种次要 LHC）的猝灭机制。我们的研究表明，LH 和猝灭状态之间的转换比之前认为的要复杂。该蛋白的腔侧发生了几种构象，并且以不同的方式影响色素的相对几何形状和相互作用。此外，我们表明，局部在单个叶绿素-类胡萝卜素对上的猝灭机制是不够的，而是许多叶绿素同时参与。在这种弥散机制中，除了通常建议的库仑相互作用之外，还必须考虑每个类胡萝卜素与不同叶绿素之间的短程相互作用以及由蛋白质介导的类胡萝卜素激发能的调谐。
