The light-dependent reactions of photosynthesis take place in the plant chloroplast thylakoid membrane, a complex three-dimensional structure divided into the stacked grana and unstacked stromal lamellae domains. Plants regulate the macro-organization of photosynthetic complexes within the thylakoid membrane to adapt to changing environmental conditions and avoid oxidative stress. One such mechanism is the state transition that regulates photosynthetic light harvesting and electron transfer. State transitions are driven by changes in the phosphorylation of light harvesting complex II (LHCII), which cause a decrease in grana diameter and stacking, a decrease in energetic connectivity between photosystem II (PSII) reaction centers, and an increase in the relative LHCII antenna size of photosystem I (PSI) compared to PSII. Phosphorylation is believed to drive these changes by weakening the intramembrane lateral PSII-LHCII and LHCII-LHCII interactions and the intermembrane stacking interactions between these complexes, while simultaneously increasing the affinity of LHCII for PSI. We investigated the relative roles and contributions of these three types of interaction to state transitions using a lattice-based model of the thylakoid membrane based on existing structural data, developing a novel algorithm to simulate protein complex dynamics. Monte Carlo simulations revealed that state transitions are unlikely to lead to a large-scale migration of LHCII from the grana to the stromal lamellae. Instead, the increased light harvesting capacity of PSI is largely due to the more efficient recruitment of LHCII already residing in the stromal lamellae into PSI-LHCII supercomplexes upon its phosphorylation. Likewise, the increased light harvesting capacity of PSII upon dephosphorylation was found to be driven by a more efficient recruitment of LHCII already residing in the grana into functional PSII-LHCII clusters, primarily driven by lateral interactions.

中文翻译：

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模拟 LHCII-LHCII、PSII-LHCII 和 PSI-LHCII 相互作用在状态转换中的作用

光合作用的光依赖反应发生在植物叶绿体类囊体膜中，这是一种复杂的三维结构，分为堆叠的颗粒和未堆叠的基质薄片结构域。植物调节类囊体膜内光合复合物的宏观组织，以适应不断变化的环境条件并避免氧化应激。一种这样的机制是调节光合光收集和电子转移的状态转变。状态转变是由光捕获复合物 II (LHCII) 磷酸化的变化驱动的，这会导致颗粒直径和堆积减小、光系统 II (PSII) 反应中心之间的能量连接性降低以及相对 LHCII 天线的增加与 PSII 相比，光系统 I (PSI) 的大小。磷酸化被认为通过削弱膜内侧向 PSII-LHCII 和 LHCII-LHCII 相互作用以及这些复合物之间的膜间堆积相互作用来驱动这些变化，同时增加 LHCII 对 PSI 的亲和力。我们使用基于现有结构数据的基于晶格的类囊体膜模型研究了这三种相互作用对状态转换的相对作用和贡献，开发了一种新的算法来模拟蛋白质复合体动力学。蒙特卡罗模拟表明，状态转变不太可能导致 LHCII 从颗粒到基质薄片的大规模迁移。反而，PSI 增加的光捕获能力主要是由于在其磷酸化后更有效地将已经存在于基质薄片中的 LHCII 募集到 PSI-LHCII 超复合物中。同样，发现去磷酸化后 PSII 的光捕获能力增加是由更有效地将已经存在于谷物中的 LHCII 募集到功能性 PSII-LHCII 簇中驱动的，主要由横向相互作用驱动。