Structure of the complex I-like molecule NDH of oxygenic photosynthesis
Structure of the complex I-like molecule NDH of oxygenic photosynthesis
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DOI：
10.1038/s41586-019-0921-0
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发表时间：
2019-02-21
期刊：
影响因子：
64.8
通讯作者：
Davies, Karen M.
中科院分区：
文献类型：
--
作者：
Laughlin, Thomas G.;Bayne, Andrew N.;Davies, Karen M.
围绕光系统I（PSI）的循环电子流是光合生物平衡有效光合作用所需的ATP和NADPH水平的机制（1，2）。NAD（P）H脱氨酶样复合物（NDH）是大多数产氧光合生物中该途径的关键组分（3，4），并且是结构仍然未知的最后一种大型光合膜-蛋白质复合物。与呼吸系统NADH脱氢酶复合物（复合物I）相关，NDH将来自PSI的电子转移到质体醌库，同时泵送质子穿过类囊体膜，从而增加每个还原的NADP+分子产生的ATP量（4，5）。NDH具有14个核心复合物I亚基中的11个，以及从蓝细菌到植物保守的几个含氧光合作用特异性（OPS）亚基（3，6）。然而，参与从NAD（P）H接受电子的三个核心复合物I亚基在NDH 3、5、6中明显不存在，因此不清楚NDH如何获得电子并将电子转移到质体醌。有人提出，OPS亚基-特别是NdhS-使NDH能够接受来自其电子供体铁氧还蛋白的电子（3- 5，7）。在这里，我们报告了一个3.1埃的结构的0.42-MDa NDH复杂的嗜热蓝细菌Thermosynechococcus elongatus BP-1，通过单粒子低温电子显微镜获得。我们的图谱揭示了NDH复合物中主要OPS亚基的结构和排列，以及在外周臂中接近质体醌结合位点的一个意想不到的辅因子。OPS亚基的位置支持电子传递的作用，并在外周臂的顶点定义了两个潜在的铁氧还蛋白结合位点。这些结果表明NDH可能具有几种电子传递途径，这将用于使质体醌还原最大化并避免半质体醌自由基的有害脱靶化学。
Cyclic electron flow around photosystem I (PSI) is a mechanism by which photosynthetic organisms balance the levels of ATP and NADPH necessary for efficient photosynthesis(1,2). NAD(P)H dehydrogenase-like complex (NDH) is a key component of this pathway in most oxygenic photosynthetic organisms(3,4) and is the last large photosynthetic membrane-protein complex for which the structure remains unknown. Related to the respiratory NADH dehydrogenase complex (complex I), NDH transfers electrons originating from PSI to the plastoquinone pool while pumping protons across the thylakoid membrane, thereby increasing the amount of ATP produced per NADP+ molecule reduced(4,5). NDH possesses 11 of the 14 core complex I subunits, as well as several oxygenic-photosynthesis-specific (OPS) subunits that are conserved from cyanobacteria to plants(3,6). However, the three core complex I subunits that are involved in accepting electrons from NAD(P) H are notably absent in NDH3,5,6, and it is therefore not clear how NDH acquires and transfers electrons to plastoquinone. It is proposed that the OPS subunits-specifically NdhS-enable NDH to accept electrons from its electron donor, ferredoxin(3-5,7). Here we report a 3.1 angstrom structure of the 0.42-MDa NDH complex from the thermophilic cyanobacterium Thermosynechococcus elongatus BP-1, obtained by single-particle cryo-electron microscopy. Our maps reveal the structure and arrangement of the principal OPS subunits in the NDH complex, as well as an unexpected cofactor close to the plastoquinone-binding site in the peripheral arm. The location of the OPS subunits supports a role in electron transfer and defines two potential ferredoxin-binding sites at the apex of the peripheral arm. These results suggest that NDH could possess several electron transfer routes, which would serve to maximize plastoquinone reduction and avoid deleterious off-target chemistry of the semi-plastoquinone radical.