A favorable path to domain separation in the orange carotenoid protein
A favorable path to domain separation in the orange carotenoid protein
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DOI：
10.1002/pro.4273
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发表时间：
2021-06
期刊：
影响因子：
8
通讯作者：
Mahmoud Sharawy;Natalia B Pigni;Eric R. May;José A. Gascón
中科院分区：
文献类型：
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作者：
Mahmoud Sharawy;Natalia B Pigni;Eric R. May;José A. Gascón
橙子类胡萝卜素蛋白（OCP）是蓝藻中负责非光化学猝灭（NPQ）的一种防御机制，可抵御过度光照条件的潜在破坏作用。这种可溶性双结构域蛋白在光活化后经历深刻的构象变化，涉及类胡萝卜素在腔内的移位，随后是结构域分离。结构域分离是OCP光循环中的关键步骤，因为它暴露N末端结构域（NTD）以进行藻胆体的淬灭。关于OCP结构域分离的机制和能量学的许多细节仍然未知。在这项工作中，我们应用代谢动力学来阐明导致OCP活性，结构域分离形式的蛋白质重排。我们发现，易位的酮类胡萝卜素黄质具有深远的影响，充满活力的景观和结构域分离，只有成为有利的易位。我们进一步探索，表征和验证的自由能表面（FES）使用平衡模拟从不同的状态开始的FES。通过路径优化方法，我们表征了域分离的最可能的路径，并揭示了沿该路径的障碍沿着。我们发现，自由能垒是相对较小的（1毫秒）。总的来说，我们的研究结果提供了详细的信息，对黄质易位的要求之前域分离和一个积极可行的解离途径。
The orange carotenoid protein (OCP) is responsible for nonphotochemical quenching (NPQ) in cyanobacteria, a defense mechanism against potentially damaging effects of excess light conditions. This soluble two‐domain protein undergoes profound conformational changes upon photoactivation, involving translocation of the ketocarotenoid inside the cavity followed by domain separation. Domain separation is a critical step in the photocycle of OCP because it exposes the N‐terminal domain (NTD) to perform quenching of the phycobilisomes. Many details regarding the mechanism and energetics of OCP domain separation remain unknown. In this work, we apply metadynamics to elucidate the protein rearrangements that lead to the active, domain‐separated, form of OCP. We find that translocation of the ketocarotenoid canthaxanthin has a profound effect on the energetic landscape and that domain separation only becomes favorable following translocation. We further explore, characterize, and validate the free energy surface (FES) using equilibrium simulations initiated from different states on the FES. Through pathway optimization methods, we characterize the most probable path to domain separation and reveal the barriers along that pathway. We find that the free energy barriers are relatively small (1 ms). Overall, our results provide detailed information on the requirement for canthaxanthin translocation to precede domain separation and an energetically feasible pathway to dissociation.