The CHLI1 subunit of Arabidopsis thaliana magnesium chelatase is a target protein of the chloroplast thioredoxin
The CHLI1 subunit of Arabidopsis thaliana magnesium chelatase is a target protein of the chloroplast thioredoxin
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DOI：
10.1074/jbc.m703324200
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发表时间：
2007-07-06
影响因子：
4.8
通讯作者：
Masuda, Tatsuru
中科院分区：
文献类型：
--
作者：
Ikegami, Akinori;Yoshimura, Naho;Masuda, Tatsuru
镁螯合酶将镁插入原卟啉IX是植物叶绿体中叶绿素生物合成途径中的关键步骤。镁螯合酶的Chli亚基对ATP的水解是这一反应的重要组成部分，而该酶的活性是决定镁插入叶绿素分子(四吡咯环)的速率的主要因素。高等植物CHLI含有高度保守的半胱氨酸残基，最近被鉴定为硫氧还蛋白靶蛋白蛋白质组(Balmer，Y.，Koller，A.，del Val，G.，Manieri，W.，Schurmann，P.和Buchanan，B.(2003)Proc)的候选蛋白质。娜塔莉。阿卡德。SCI。美国100,370-375)。为了研究硫氧还蛋白对镁螯合酶的调节，我们首先研究了硫氧还蛋白对拟南芥CHLI的主要亚型CHLI1 ATPase活性的影响。重组CHLI1的ATPase活性在氧化过程中完全失活，硫氧还蛋白辅助还原后很容易恢复，提示CHLI1是硫氧还蛋白的靶蛋白。此外，我们还在CHLI1蛋白的C-末端螺旋结构域上发现了一个关键的二硫键，它可能调节核苷酸与N-末端催化结构域的结合。在体内，CHLI的氧化还原状态也被发现以一种光依赖的方式改变。此外，我们成功地观察到还原对分离的叶绿体中镁螯合酶活性的刺激。我们的发现有力地表明，叶绿素的生物合成受到叶绿体生物发生调控网络的影响，以协调它们与叶绿体中的光合作用途径。
Insertion of magnesium into protoporphyrin IX by magnesium chelatase is a key step in the chlorophyll biosynthetic pathway, which takes place in plant chloroplasts. ATP hydrolysis by the CHLI subunit of magnesium chelatase is an essential component of this reaction, and the activity of this enzyme is a primary determinant of the rate of magnesium insertion into the chlorophyll molecule ( tetrapyrrole ring). Higher plant CHLI contains highly conserved cysteine residues and was recently identified as a candidate protein in a proteomic screen of thioredoxin target proteins (Balmer, Y., Koller, A., del Val, G., Manieri, W., Schurmann, P., and Buchanan, B. B.( 2003) Proc. Natl. Acad. Sci. U. S. A. 100,370-375). To study the thioredoxin-dependent regulation of magnesium chelatase, we first investigated the effect of thioredoxin on the ATPase activity of CHLI1, a major isoform of CHLI in Arabidopsis thaliana. The ATPase activity of recombinant CHLI1 was found to be fully inactivated by oxidation and easily recovered by thioredoxin-assisted reduction, suggesting that CHLI1 is a target protein of thioredoxin. Moreover, we identified one crucial disulfide bond located in the C-terminal helical domain of CHLI1 protein, which may regulate the binding of the nucleotide to the N-terminal catalytic domain. The redox state of CHLI was also found to alter in a light-dependent manner in vivo. Moreover, we successfully observed stimulation of the magnesium chelatase activity in isolated chloroplasts by reduction. Our findings strongly suggest that chlorophyll biosynthesis is subject to chloroplast biogenesis regulation networks to coordinate them with the photosynthetic pathways in chloroplasts.