Department of Physics and Astronomy and Institute for Lasers, Life and Biophotonics, Faculty of Science, Vrije Universiteit Amsterdam, de Boelelaan 1081, 1081 HV Amsterdam, The Netherlands.
Institute for Integrative Biology of the Cell (I2BC), CNRS, CEA, Université Paris-Sud, Université Paris-Saclay, 91198 Gif sur Yvette ,France.
J Am Chem Soc. 2024 Aug 7;146(31):21913-21921. doi: 10.1021/jacs.4c06695. Epub 2024 Jul 26.
Cyanobacteria were the first microorganisms that released oxygen into the atmosphere billions of years ago. To do it safely under intense sunlight, they developed strategies that prevent photooxidation in the photosynthetic membrane, by regulating the light-harvesting activity of their antenna complexes-the phycobilisomes-via the orange-carotenoid protein (OCP). This water-soluble protein interacts with the phycobilisomes and triggers nonphotochemical quenching (NPQ), a mechanism that safely dissipates overexcitation in the membrane. To date, the mechanism of action of OCP in performing NPQ is unknown. In this work, we performed ultrafast spectroscopy on a minimal NPQ system composed of the active domain of OCP bound to the phycobilisome core. The use of this system allowed us to disentangle the signal of the carotenoid from that of the bilins. Our results demonstrate that the binding to the phycobilisomes modifies the structure of the ketocarotenoid associated with OCP. We show that this molecular switch activates NPQ, by enabling excitation-energy transfer from the antenna pigments to the ketocarotenoid.
蓝藻是数十亿年前向大气中释放氧气的第一种微生物。为了在强烈的阳光下安全地进行光合作用，它们通过调节天线复合物——藻胆体的光捕获活性，开发了防止光合作用膜光氧化的策略——通过橙色类胡萝卜素蛋白（OCP）。这种水溶性蛋白与藻胆体相互作用，并触发非光化学猝灭（NPQ），这是一种安全地耗散膜中超激发的机制。迄今为止，OCP 在执行 NPQ 中的作用机制尚不清楚。在这项工作中，我们对由与藻胆体核心结合的 OCP 活性结构域组成的最小 NPQ 系统进行了超快光谱研究。使用该系统，我们能够将类胡萝卜素的信号与藻胆素的信号分离开来。我们的结果表明，与藻胆体的结合改变了与 OCP 相关的酮类胡萝卜素的结构。我们表明，这种分子开关通过使天线色素的激发能转移到酮类胡萝卜素来激活 NPQ。
