Major light-harvesting complex of photosystem II (LHCII) plays a dual role in light-harvesting and excited energy dissipation to protect photodamage from excess energy. The regulatory switch is induced by increased acidity, temperature or both. However, the molecular origin of the protein dynamics at the atomic level is still unknown. We carried out temperature-jump time-resolved infrared spectroscopy and molecular dynamics simulations to determine the energy quenching dynamics and conformational changes of LHCII trimers. We found that the spontaneous formation of a pair of local α-helices from the 3₁₀-helix E/loop and the C-terminal coil of the neighboring monomer, in response to the increased environmental temperature and/or acidity, induces a scissoring motion of transmembrane helices A and B, shifting the conformational equilibrium to a more open state, with an increased angle between the associated carotenoids. The dynamical and allosteric conformation change leads to close contacts between carotenoid lutein 1 and chlorophyll pigment 612, facilitating the fluorescence quenching. Based on these results, we suggest a unified mechanism by which the LHCII trimer controls the dissipation of excess excited energy in response to increased temperature and acidity, as an intrinsic result of intense sun light in plant photosynthesis.

光系统II（LHCII）的主要光收集复合体在光收集和激发的能量消散中起双重作用，以保护光损伤免受过量能量的影响。调节开关是由增加的酸度，温度或两者引起的。然而，在原子水平上蛋白质动力学的分子起源仍然是未知的。我们进行了温度跃迁时间分辨红外光谱和分子动力学模拟，以确定LHCII三聚体的能量猝灭动力学和构象变化。我们发现，从3 _10开始，自然形成了一对局部α螺旋。-螺旋E /环和邻近单体的C末端线圈响应于升高的环境温度和/或酸度，引起跨膜螺旋A和B的剪切运动，从而将构象平衡转变为更开放的状态，相关类胡萝卜素之间的夹角增加。动态和变构构象变化导致类胡萝卜素叶黄素1和叶绿素色素612之间的紧密接触，从而促进了荧光猝灭。基于这些结果，我们提出了一种统一的机制，LHCII三聚体通过这种机制来控制过量的激发能量的耗散，以响应温度和酸度的升高，这是植物光合作用中强烈的阳光的内在结果。