Participation of Chlorophyll b Reductase in the Initial Step of the Degradation of Light-harvesting Chlorophyll a/b-Protein Complexes in Arabidopsis
Participation of Chlorophyll b Reductase in the Initial Step of the Degradation of Light-harvesting Chlorophyll a/b-Protein Complexes in Arabidopsis
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DOI：
10.1074/jbc.m109.008912
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发表时间：
2009-06-26
影响因子：
4.8
通讯作者：
Tanaka, Ayumi
中科院分区：
文献类型：
--
作者：
Horie, Yukiko;Ito, Hisashi;Tanaka, Ayumi
光系统II的捕光叶绿素a/b-蛋白复合物（LHCII）是绿色植物中含量最丰富的膜蛋白，其降解是植物适应强光环境和衰老过程中氮（N）和碳（C）恢复的关键过程。然而，LHCII降解的分子机制在很大程度上是未知的。在这里，我们报告，叶绿素B还原酶，催化叶绿素B降解的第一步，在LHCII降解中起着核心作用。当拟南芥中叶绿素B还原酶NOL和NYC 1的基因被破坏时，叶绿素B和LHC II在衰老过程中没有降解，而其他色素复合物完全消失。当纯化的三聚体LHCII与在大肠杆菌中表达的重组叶绿素B还原酶（NOL）温育时，LHCII中的叶绿素B转化为7-羟甲基叶绿素a。伴随着这种转换，叶绿素从LHCII脱辅基蛋白中释放出来，直到LHCII中的所有叶绿素分子从复合物中解离出来。叶绿素耗尽LHCII脱辅基蛋白没有解离成单体形式，但仍然在三聚体形式。基于这些结果，我们提出了新的假设，即叶绿素B还原酶催化LHCII降解的初始步骤，三聚体LHCII是LHCII降解的底物。
The light-harvesting chlorophyll a/b-protein complex of photosystem II (LHCII) is the most abundant membrane protein in green plants, and its degradation is a crucial process for the acclimation to high light conditions and for the recovery of nitrogen (N) and carbon (C) during senescence. However, the molecular mechanism of LHCII degradation is largely unknown. Here, we report that chlorophyll b reductase, which catalyzes the first step of chlorophyll b degradation, plays a central role in LHCII degradation. When the genes for chlorophyll b reductases NOL and NYC1 were disrupted in Arabidopsis thaliana, chlorophyll b and LHCII were not degraded during senescence, whereas other pigment complexes completely disappeared. When purified trimeric LHCII was incubated with recombinant chlorophyll b reductase (NOL), expressed in Escherichia coli, the chlorophyll b in LHCII was converted to 7-hydroxymethyl chlorophyll a. Accompanying this conversion, chlorophylls were released from LHCII apoproteins until all the chlorophyll molecules in LHCII dissociated from the complexes. Chlorophyll-depleted LHCII apoproteins did not dissociate into monomeric forms but remained in the trimeric form. Based on these results, we propose the novel hypothesis that chlorophyll b reductase catalyzes the initial step of LHCII degradation, and that trimeric LHCII is a substrate of LHCII degradation.