Department of Chemistry, University of California, Berkeley, California 94720, United States.
Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States.
J Phys Chem B. 2024 Aug 22;128(33):7941-7953. doi: 10.1021/acs.jpcb.4c02508. Epub 2024 Aug 14.
The water-splitting capability of Photosystem II (PSII) of plants and green algae requires the system to balance efficient light harvesting along with effective photoprotection against excitation in excess of the photosynthetic capacity, particularly under the naturally fluctuating sunlight intensity. The comparatively flat energy landscape of the multicomponent structure, inferred from the spectra of the individual pigment-protein complexes and the rather narrow and featureless absorption spectrum, is well known. However, how the combination of the required functions emerges from the interactions among the multiple components of the PSII supercomplex (PSII-SC) cannot be inferred from the individual pigment-protein complexes. In this work, we investigate the energy transfer dynamics of the CS-type PSII-SC with a combined spectroscopic and modeling approach. Specifically, two-dimensional electronic-vibrational (2DEV) spectroscopy provides enhanced spectral resolution and the ability to map energy evolution in real space, while the quantum dynamical simulation allows complete kinetic modeling of the 210 chromophores. We demonstrate that additional pathways emerge within the supercomplex. In particular, we show that excitation energy can leave the vicinity of the charge separation components, the reaction center (RC), faster than it can transfer to it. This enables activatable quenching centers in the periphery of the PSII-SC to be effective in removing excessive energy in cases of overexcitation. Overall, we provide a quantitative description of how the seemingly contradictory functions of PSII-SC arise from the combination of its individual components. This provides a fundamental understanding that will allow further improvement of artificial solar energy devices and bioengineering processes for increasing crop yield.
植物和绿藻的光系统 II（PSII）的水分解能力要求该系统在有效地光捕获的同时，平衡有效地光保护，以防止光合作用能力过剩的激发，尤其是在自然波动的阳光强度下。从各个色素-蛋白复合物的光谱和相当狭窄且无特征的吸收光谱推断出，多组分结构的相对平坦的能量景观是众所周知的。然而，从 PSII 超复合物（PSII-SC）的多个组件之间的相互作用中如何出现所需的功能，不能从单个色素-蛋白复合物中推断出来。在这项工作中，我们通过综合光谱和建模方法研究 CS 型 PSII-SC 的能量转移动力学。具体来说，二维电子-振动（2DEV）光谱提供了增强的光谱分辨率和在实空间中映射能量演化的能力，而量子动力学模拟允许对 210 个发色团进行完整的动力学建模。我们证明了在超复合物中出现了额外的途径。特别是，我们表明，激发能量可以比它转移到附近的电荷分离组件，即反应中心（RC）更快地离开。这使得 PSII-SC 外围的可激活猝灭中心在过激发的情况下能够有效地去除多余的能量。总体而言，我们提供了一种定量描述，说明 PSII-SC 的看似矛盾的功能如何从其各个组件的组合中产生。这提供了一个基本的理解，将允许进一步改进人工太阳能设备和生物工程过程，以提高作物产量。
