Isolation of the elusive supercomplex that drives cyclic electron flow in photosynthesis
Isolation of the elusive supercomplex that drives cyclic electron flow in photosynthesis
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DOI：
10.1038/nature08885
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发表时间：
2010-04-22
期刊：
影响因子：
64.8
通讯作者：
Minagawa, Jun
中科院分区：
文献类型：
--
作者：
Iwai, Masakazu;Takizawa, Kenji;Minagawa, Jun
光合光反应在叶绿体的类囊体膜中建立电子流，导致参与碳固定的ATP和NADPH的产生。电子流存在两种模式：从水到NADP 1的线性电子流（LEF）和围绕PSI的循环电子流（CEF）。虽然CEF对于满足ATP的不同需求是必不可少的，但确切的分子和操作位点尚不清楚。在绿色莱茵衣藻中，电子流在PSII的优先激发下从LEF转移到CEF（参考文献3），这是由PSII和PSI之间的能量平衡机制（状态转换（4））引起的。在此，我们从C. coli中分离到一种由PSI及其自身的捕光复合物（LHCI）、PSII捕光复合物（LHCII）、细胞色素B（6）f复合物（Cyt bf）、铁氧还蛋白（Fd）-NADPH氧化还原酶（FNR）和膜整合蛋白PGRL 1（参考文献5）组成的蛋白超复合物。在PSII有利的条件下培养reinhardtii细胞。光谱分析表明，在光照下，PSI下游的还原当量被转移到Cyt bf，而氧化的PSI被Cyt bf的还原当量重新还原，表明这种超复合物参与CEF（补充图1）。因此，PSI-LHCI-LHCII-FNR-Cyt bf-PGRL 1超复合物的形成和解离不仅控制了两个光系统的能量平衡，而且转换了光合电子流的模式。
Photosynthetic light reactions establish electron flow in the chloroplast's thylakoid membranes, leading to the production of the ATP and NADPH that participate in carbon fixation. Two modes of electron flow exist-linear electron flow (LEF) from water to NADP 1 via photosystem (PS) II and PSI in series(1) and cyclic electron flow (CEF) around PSI (ref. 2). Although CEF is essential for satisfying the varying demand for ATP, the exact molecule(s) and operational site are as yet unclear. In the green alga Chlamydomonas reinhardtii, the electron flow shifts from LEF to CEF on preferential excitation of PSII (ref. 3), which is brought about by an energy balancing mechanism between PSII and PSI (state transitions(4)). Here, we isolated a protein super-complex composed of PSI with its own light-harvesting complex (LHCI), the PSII light-harvesting complex (LHCII), the cytochrome b(6)f complex (Cyt bf), ferredoxin (Fd)-NADPH oxidoreductase (FNR), and the integral membrane protein PGRL1 (ref. 5) from C. reinhardtii cells under PSII-favouring conditions. Spectroscopic analyses indicated that on illumination, reducing equivalents from downstream of PSI were transferred to Cyt bf, whereas oxidised PSI was re-reduced by reducing equivalents from Cyt bf, indicating that this supercomplex is engaged in CEF (Supplementary Fig. 1). Thus, formation and dissociation of the PSI-LHCI-LHCII-FNR-Cyt bf-PGRL1 supercomplex not only controlled the energy balance of the two photosystems, but also switched the mode of photosynthetic electron flow.