A.N. Bach Institute of Biochemistry, Federal Research Centre of Biotechnology of the Russian Academy of Sciences, Moscow 119071, Russia.
M.V. Lomonosov Moscow State University, Faculty of Biology, Moscow 119991, Russia.
Int J Biol Macromol. 2024 Jan;254(Pt 2):127874. doi: 10.1016/j.ijbiomac.2023.127874. Epub 2023 Nov 7.
The Orange Carotenoid Protein (OCP) is a unique photoreceptor crucial for cyanobacterial photoprotection. Best studied Synechocystis sp. PCC 6803 OCP belongs to the large OCP1 family. Downregulated by the Fluorescence Recovery Protein (FRP) in low-light, high-light-activated OCP1 binds to the phycobilisomes and performs non-photochemical quenching. Recently discovered families OCP2 and OCP3 remain structurally and functionally underexplored, and no systematic comparative studies have ever been conducted. Here we present two first crystal structures of OCP2 from morphoecophysiologically different cyanobacteria and provide their comprehensive structural, spectroscopic and functional comparison with OCP1, the recently described OCP3 and all-OCP ancestor. Structures enable correlation of spectroscopic signatures with the effective number of hydrogen and discovered here chalcogen bonds anchoring the ketocarotenoid in OCP, as well as with the rotation of the echinenone's β-ionone ring in the CTD. Structural data also helped rationalize the observed differences in OCP/FRP and OCP/phycobilisome functional interactions. These data are expected to foster OCP research and applications in optogenetics, targeted carotenoid delivery and cyanobacterial biomass engineering.
橙体蛋白（OCP）是一种独特的光感受器，对蓝藻的光保护至关重要。研究最为深入的 Synechocystis sp. PCC 6803 OCP 属于大型 OCP1 家族。在低光下，由荧光恢复蛋白（FRP）下调，高光激活的 OCP1 与藻胆体结合并进行非光化学猝灭。最近发现的 OCP2 和 OCP3 家族在结构和功能上仍未得到充分探索，也从未进行过系统的比较研究。在这里，我们展示了两种来自形态生理不同蓝藻的 OCP2 的首个晶体结构，并对其与 OCP1、最近描述的 OCP3 和全-OCP 祖先的结构、光谱和功能进行了全面比较。结构使我们能够将光谱特征与有效的氢键数量以及在这里发现的将酮类胡萝卜素固定在 OCP 中的硫属键相关联，以及与 CTD 中echinenone 的β-紫罗兰酮环的旋转相关联。结构数据还有助于解释观察到的 OCP/FRP 和 OCP/藻胆体功能相互作用的差异。这些数据有望促进 OCP 在光遗传学、靶向类胡萝卜素传递和蓝藻生物质工程中的研究和应用。
