Structures of a phycobilisome in light-harvesting and photoprotected states
Structures of a phycobilisome in light-harvesting and photoprotected states
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DOI：
10.1038/s41586-022-05156-4
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发表时间：
2022-08-31
期刊：
影响因子：
64.8
通讯作者：
Kerfeld, Cheryl A.
中科院分区：
文献类型：
--
作者：
Dominguez-Martin, Maria Agustina;Sauer, Paul, V;Kerfeld, Cheryl A.
藻胆体(PBS)结构是蓝藻和红藻(1，2)中复杂的触角。这些大型蛋白质复合体捕捉入射的阳光，并通过嵌入的色素分子网络将能量转移到光合作用反应中心。然而，光采集也必须与光损伤的风险相平衡。一种已知的光保护模式是由橙色类胡萝卜素蛋白(OCP)介导的，当光强较高时，OCP与PBS结合，介导光保护非光化学猝灭(3-6)。在这里，我们使用低温电子显微镜来解析模式蓝藻聚球藻6.2MDA PBS的四种结构，有OCP结合的和没有OCP结合的。PCC 6803。这些结构包含一个先前未描述的连接蛋白，它与PBS面向膜的一侧结合。对于未猝灭的PbS，结构还揭示了天线的三种不同构象状态，其中两种以前是未知的。这种构象状态是由两个杆的位置转换引起的，并可能构成一种新的光收集调节模式。三种PBS构象中只有一种可以与OCP结合，这表明并不是所有的PBS都同样容易受到非光化学猝灭的影响。在OCP-PBS复合体中，猝灭是通过四个34 kDa的OCP结合实现的，这些OCP被组织成两个二聚体。该复合体揭示了OCP的活性形式的结构，在该结构中，其调节的羧基末端结构域发生了约60埃的位移。最后，通过结合我们的结构和光谱性质(7)，我们阐明了PbS在猝灭和捕光状态下的能量转移途径。总而言之，我们的结果为控制蓝藻采光的生物物理基础提供了详细的见解。这些数据还对自然和人工采光系统中的生物工程PBS监管有影响。
Phycobilisome (PBS) structures are elaborate antennae in cyanobacteria and red algae(1,2). These large protein complexes capture incident sunlight and transfer the energy through a network of embedded pigment molecules called bilins to the photosynthetic reaction centres. However, light harvesting must also be balanced against the risks of photodamage. A known mode of photoprotection is mediated by orange carotenoid protein (OCP), which binds to PBS when light intensities are high to mediate photoprotective, non-photochemical quenching(3-6). Here we use cryogenic electron microscopy to solve four structures of the 6.2 MDa PBS, with and without OCP bound, from the model cyanobacterium Synechocystis sp. PCC 6803. The structures contain a previously undescribed linker protein that binds to the membrane-facing side of PBS. For the unquenched PBS, the structures also reveal three different conformational states of the antenna, two previously unknown. The conformational states result from positional switching of two of the rods and may constitute a new mode of regulation of light harvesting. Only one of the three PBS conformations can bind to OCP, which suggests that not every PBS is equally susceptible to non-photochemical quenching. In the OCP-PBS complex, quenching is achieved through the binding of four 34 kDa OCPs organized as two dimers. The complex reveals the structure of the active form of OCP, in which an approximately 60 angstrom displacement of its regulatory carboxy terminal domain occurs. Finally, by combining our structure with spectroscopic properties(7), we elucidate energy transfer pathways within PBS in both the quenched and light-harvesting states. Collectively, our results provide detailed insights into the biophysical underpinnings of the control of cyanobacterial light harvesting. The data also have implications for bioengineering PBS regulation in natural and artificial light-harvesting systems.