Dipartimento di Chimica e Chimica Industriale, University of Pisa, via G. Moruzzi 13, 56124 Pisa, Italy.
Physics Department, Trento University, Via Sommarive 14, 38128 Povo, Trento, Italy.
J Am Chem Soc. 2020 Dec 30;142(52):21829-21841. doi: 10.1021/jacs.0c10461. Epub 2020 Dec 17.
Light-harvesting in photosynthesis is accompanied by photoprotective processes. In cyanobacteria, the photoprotective role is played by a specialized complex, the orange carotenoid protein, which is activated by strong blue-green light. This photoactivation involves a unique series of structural changes which terminate with an opening of the complex into two separate domains, one of which acts as a quencher for the light-harvesting complexes. Many experimental studies have tried to reveal the molecular mechanisms through which the energy absorbed by the carotenoid finally leads to the large conformational change of the complex. Here, for the first time, these mechanisms are revealed by simulating at the atomistic level the whole dynamics of the complex through an effective combination of enhanced sampling techniques. On the basis of our findings, we can conclude that the carotenoid does not act as a spring that, releasing its internal strain, induces the dissociation, as was previously proposed, but as a "latch" locking together the two domains. The photochemically triggered displacement of the carotenoid breaks this balance, allowing the complex to dissociate.
光合作用中的光捕获伴随着光保护过程。在蓝藻中，光保护作用是由一种特殊的复合物——橙色类胡萝卜素蛋白来完成的，这种复合物在强蓝绿光的作用下被激活。这种光激活涉及到一系列独特的结构变化，最终导致复合物打开成两个独立的结构域，其中一个结构域充当光捕获复合物的淬灭剂。许多实验研究试图揭示色素分子吸收能量最终导致复合物发生大的构象变化的分子机制。在这里，我们首次通过有效结合增强采样技术，在原子水平上模拟整个复合物的动力学，揭示了这些机制。根据我们的发现，我们可以得出结论，类胡萝卜素不是作为一个弹簧，通过释放其内部应变来诱导复合物的解离，就像以前提出的那样，而是作为一个“闩锁”将两个结构域锁定在一起。光化学触发的类胡萝卜素位移打破了这种平衡，使得复合物能够解离。
