Disentangling protein and lipid interactions that control a molecular switch in photosynthetic light harvesting
Disentangling protein and lipid interactions that control a molecular switch in photosynthetic light harvesting
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DOI：
10.1016/j.bbamem.2016.10.010
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发表时间：
2017-01-01
影响因子：
3.4
通讯作者：
Pandit, Anjali
中科院分区：
文献类型：
--
作者：
Crisafi, Emanuela;Pandit, Anjali
在植物和藻类的光合作用装置中，主要的捕光复合体(LHCII)收集激发并将其输送到发生电荷分离的光合作用反应中心。在强光条件下，光合膜的重塑和蛋白质构象的变化产生一种光保护状态，在这种状态下，激发被迅速熄灭，以避免光损伤。猝灭状态与蛋白质聚集有关，但LHCII复合体也被认为具有在捕光和荧光猝灭构象状态之间转换的本征能力。为了弄清蛋白质-蛋白质和蛋白质-脂相互作用对LHCII光保护开关的影响，我们比较了极低蛋白质/脂比的LHCII脂纳米盘和蛋白质脂质体的结构和荧光性质。我们证明了LHCII蛋白在纳米盘和高度稀释的蛋白脂质体中处于完全荧光状态。增加蛋白质密度会导致向轻度猝灭状态的转变，在摩尔蛋白质与脂肪的比率为0.001时达到平台期，并具有使人想起体内捕光状态的荧光产量。猝灭的低起始值强烈地表明LHCII-LHCII吸引相互作用发生在膜内。在低蛋白质密度下的跃迁不涉及激子圆二色谱的强烈变化，而不同于在很高的蛋白质密度下发生的跃迁，后者包括涉及叶绿素611和612的强烈荧光猝灭和圆二色光谱变化，这与所提出的光保护机制的猝灭位置有关。(C)2016爱思唯尔B.V.保留所有权利。
In the photosynthetic apparatus of plants and algae, the major Light-Harvesting Complexes (LHCII) collect excitations and funnel these to the photosynthetic reaction center where charge separation takes place. In excess light conditions, remodeling of the photosynthetic membrane and protein conformational changes produces a photoprotective state in which excitations are rapidly quenched to avoid photodamage. The quenched states are associated with protein aggregation, however the LHCII complexes are also proposed to have an intrinsic capacity to shift between light harvesting and fluorescence-quenched conformational states. To disentangle the effects of protein-protein and protein-lipid interactions on the LHCII photoprotective switch, we compared the structural and fluorescent properties of LHCII lipid nanodiscs and proteoliposomes with very low protein-to-lipid ratios. We demonstrate that LHCII proteins adapta fully fluorescent state in nanodiscs and in proteoliposomes with highly diluted protein densities. Increasing the protein density induces a transition into a mildly-quenched state that reaches a plateau at a molar protein-to-lipid ratio of 0.001 and has a fluorescence yield reminiscent of the light-harvesting state in vivo. The low onset for quenching strongly suggests that LHCII-LHCII attractive interactions occur inside membranes. The transition at low protein densities does not involve strong changes in the excitonic circular-dichroism spectrum and is distinct from a transition occurring at very high protein densities that comprises strong fluorescence quenching and circular-dichroism spectral changes involving chlorophyll 611 and 612, correlating with proposed quencher sites of the photoprotective mechanisms. (C) 2016 Elsevier B.V. All rights reserved.