Trivial Excitation Energy Transfer to Carotenoids is an Unlikely Mechanism for Non-Photochemical Quenching in LHCII
Trivial Excitation Energy Transfer to Carotenoids is an Unlikely Mechanism for Non-Photochemical Quenching in LHCII
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微量激发能量转移到类胡萝卜素是 LHCII 中非光化学猝灭的不太可能的机制
DOI：
10.1101/2021.10.18.464810
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发表时间：
2021
期刊：
影响因子：
--
通讯作者：
Gray C
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文献类型：
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作者：
Gray C
高等植物通过非光化学猝灭（NPQ）机制保护自己免受强光照射。它涉及光系统II （PSII）天线蛋白（LHCII）采用有利于激发猝灭的构象。近年来，一些结构模型表明，猝灭过程是通过能量转移到类胡萝卜素的光禁态和短寿命态进行的。有人提出，这一途径是由少数色素相对取向的细微变化控制的。然而，s1性质的量子化学计算不是微不足道的，因此它的能量、振子强度和寿命被视为相当松散的参数。此外，这些模型要么基于单个LHCII晶体结构，要么基于单个最小值的分子动力学（MD）轨迹。在这里，我们试图通过参数化叶黄素的振动结构和弛豫动力学的可观测量，即其线性吸收（LA），瞬态吸收（TA）和双光子激发（TPE）光谱来解决这些限制。我们还分析了从LHCII自由能表面的穷举元动力学搜索中得到的一些极小值。我们发现，微不足道的，库仑介导的能量转移tos1是一种不太可能的猝灭机制，颜料的运动不足以在猝灭和未猝灭状态之间切换系统。作为淬火开关的s1能级调制同样是不可能的。此外，先前模型预测的猝灭可能是量子化学对s1振荡器强度高估的产物，真正的机制可能涉及短程相互作用和/或非平凡的分子间状态。
Higher plants defend themselves from bursts of intense light via the mechanism of Non-Photochemical Quenching (NPQ). It involves the Photosystem II (PSII) antenna protein (LHCII) adopting a conformation that favors excitation quenching. In recent years several structural models have suggested that quenching proceeds via energy transfer to the optically forbidden and short-livedS1states of a carotenoid. It was proposed that this pathway was controlled by subtle changes in the relative orientation of a small number of pigments. However, quantum chemical calculations ofS1properties are not trivial and therefore its energy, oscillator strength and lifetime are treated as rather loose parameters. Moreover, the models were based either on a single LHCII crystal structure or Molecular Dynamics (MD) trajectories about a single minimum. Here we try and address these limitations by parameterizing the vibronic structure and relaxation dynamics of lutein in terms of observable quantities, namely its linear absorption (LA), transient absorption (TA) and two-photon excitation (TPE) spectra. We also analyze a number of minima taken from an exhaustive meta-dynamical search of the LHCII free energy surface. We show that trivial, Coulomb-mediated energy transfer toS1is an unlikely quenching mechanism, with pigment movements insufficiently pronounced to switch the system between quenched and unquenched states. Modulation ofS1energy level as a quenching switch is similarly unlikely. Moreover, the quenching predicted by previous models is possibly an artifact of quantum chemical over-estimation ofS1oscillator strength and the real mechanism likely involves short-range interaction and/or non-trivial inter-molecular states.