Photoactivation Mechanism, Timing of Protein Secondary Structure Dynamics and Carotenoid Translocation in the Orange Carotenoid Protein
Photoactivation Mechanism, Timing of Protein Secondary Structure Dynamics and Carotenoid Translocation in the Orange Carotenoid Protein
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DOI：
10.1021/jacs.8b11373
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发表时间：
2019-01-09
影响因子：
15
通讯作者：
Kennis, John T. M.
中科院分区：
文献类型：
--
作者：
Konold, Patrick E.;van Stokkum, Ivo H. M.;Kennis, John T. M.
橙子类胡萝卜素蛋白（OCP）是一种非共价结合海胆酮（ECN）类胡萝卜素并介导蓝细菌光保护的双结构域光活性蛋白。在黑暗中，OCP呈现橙子的非活动状态，称为OCPO;蓝光照明导致红色活动状态，称为OCPR。OCPR状态的特征在于大规模的结构变化，其涉及C-末端和N-末端结构域的解离和分离，伴随类胡萝卜素易位到N-末端结构域中。光子吸收和OCPR态形成之间的机制和动力学结构关系在很大程度上仍然未知。在这里，我们采用时间分辨的紫外可见光和（偏振）中红外光谱来评估类胡萝卜素和蛋白质二级结构的电子和结构动力学，从飞秒到0.5 ms。我们在OCP中鉴定了迄今未鉴定的类胡萝卜素激发态，即所谓的S* 态，我们建议在打破类胡萝卜素和芳香族氨基酸之间的保守氢键相互作用的结合口袋中发挥关键作用。我们得到了一个综合反应模型，其中在皮秒内类胡萝卜素β 1环上保守的芳香侧链的氢键断裂发生在低产量下，
The orange carotenoid protein (OCP) is a two-domain photoactive protein that noncovalently binds an echinenone (ECN) carotenoid and mediates photoprotection in cyanobacteria. In the dark, OCP assumes an orange, inactive state known as OCPO; blue light illumination results in the red active state, known as OCPR. The OCPR state is characterized by large-scale structural changes that involve dissociation and separation of C-terminal and N-terminal domains accompanied by carotenoid translocation into the N-terminal domain. The mechanistic and dynamic-structural relations between photon absorption and formation of the OCPR state have remained largely unknown. Here, we employ a combination of time-resolved UV-visible and (polarized) mid-infrared spectroscopy to assess the electronic and structural dynamics of the carotenoid and the protein secondary structure, from femtoseconds to 0.5 ms. We identify a hereto unidentified carotenoid excited state in OCP, the so-called S* state, which we propose to play a key role in breaking conserved hydrogen-bond interactions between carotenoid and aromatic amino acids in the binding pocket. We arrive at a comprehensive reaction model where the hydrogen-bond rupture with conserved aromatic side chains at the carotenoid beta 1-ring in picoseconds occurs at a low yield of