CP29, a Monomeric Light-harvesting Complex II Protein, Is Essential for State Transitions in Chlamydomonas reinhardtii*
CP29, a Monomeric Light-harvesting Complex II Protein, Is Essential for State Transitions in Chlamydomonas reinhardtii*
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DOI：
10.1074/jbc.m809360200
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发表时间：
2009-03
影响因子：
4.8
通讯作者：
Ryutaro Tokutsu;Masakazu Iwai;J. Minagawa
中科院分区：
文献类型：
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作者：
Ryutaro Tokutsu;Masakazu Iwai;J. Minagawa
在放氧光合作用中，两个光系统，即光系统I（PSI）和光系统II（PSII），平行地起作用，并且它们的激发水平必须平衡以在各种光条件下保持最佳光合速率。状态转换通过重新分配捕光复合物II（LHCII）蛋白平衡两个光系统之间的激发能。在这里，我们描述了两个RNA干扰（RNAi）突变体的绿色莱茵衣藻与一个较小的单体LHCII蛋白，CP 29或CP 26，敲低。已经在PSI-LHCI超复合物中鉴定了这两种蛋白质，所述PSI-LHCI超复合物在PSII被优先激发的状态（状态2）下具有来自PSII的移动的LHCII蛋白质。我们表明，CP 29和CP 26 RNAi突变体经历减少PSII天线的大小从状态1（PSI优先激发的状态）到状态2的过渡过程中，所反映的荧光，低温荧光光谱，和功能吸收截面的非光化学猝灭。然而，在CP 29-RNAi（b4 i）突变体中，来自PSII的未对接的LHCII不与PSI重新结合，因为PSI的天线尺寸没有互补增加。然而，CP 26-RNAi（b5 i）突变体中的移动的LHCII与PSI重新缔合，PSI的PSI-LHCI/II超复合物在蔗糖密度梯度上可见。这项研究澄清，CP 29，而不是CP 26，是一个重要的组成部分，在状态转换，并表明，CP 29是至关重要的，当移动的LHCIIs重新与PSI状态2条件下。
In oxygen-evolving photosynthesis, the two photosystems, photosystem I (PSI) and photosystem II (PSII), function in parallel, and their excitation levels must be balanced to maintain an optimal photosynthetic rate under various light conditions. State transitions balance excitation energy between the two photosystems by redistributing light-harvesting complex II (LHCII) proteins. Here we describe two RNA interference (RNAi) mutants of the green alga Chlamydomonas reinhardtii with one of the minor monomeric LHCII proteins, CP29 or CP26, knocked down. These two proteins have been identified in PSI-LHCI supercomplexes that harbor mobile LHCII proteins from PSII under a state where PSII is preferentially excited (State 2). We show that both the CP29 and CP26 RNAi mutants undergo reductions in the PSII antenna size during a transition from State 1 (a state where PSI is preferentially excited) to State 2, as reflected by nonphotochemical quenching of fluorescence, low temperature fluorescence spectra, and functional absorption cross-section. However, the undocked LHCIIs from PSII do not re-associate with PSI in the CP29-RNAi (b4i) mutant because the antenna size of PSI was not complementary increased. The mobile LHCIIs in the CP26-RNAi (b5i) mutant, however, re-associate with PSI, whose PSI-LHCI/II supercomplex is visualized on a sucrose density gradient. This study clarifies that CP29, not CP26, is an essential component in state transitions and demonstrates that CP29 is crucial when mobile LHCIIs re-associate with PSI under State 2 conditions.