Orange carotenoid protein (OCP) is a carotenoid-binding protein involved in photo-protection mechanisms of cyanobacteria. Upon exposure to high light, OCP interconverts from an orange resting form (OCP^O) to a red active one (OCP^R); the mechanism of this interconversion, even if extensively studied, has still not been fully elucidated. In this work, we use multiscale atomistic models ranging from classical to hybrid quantum-classical (QM/MM) molecular dynamics to give a comprehensive molecular explanation of the drastic spectroscopic changes observed upon interconversion. The findings are finally used to formulate a new hypothesis on the role of the protein in the photoactivation mechanism.

橙色类胡萝卜素蛋白（OCP）是类胡萝卜素结合蛋白，参与蓝细菌的光保护机制。在强光下，OCP会从橙色的静止形式（OCP ^O）转换为红色的活动形式（OCP ^R）。即使进行了广泛研究，这种相互转换的机制仍未完全阐明。在这项工作中，我们使用从经典到混合量子经典（QM / MM）分子动力学的多尺度原子模型，对互转换时观察到的剧烈光谱变化给出了全面的分子解释。这些发现最终被用来对蛋白质在光激活机制中的作用提出新的假设。