Linking chlorophyll biosynthesis to a dynamic plastoquinone pool.
Linking chlorophyll biosynthesis to a dynamic plastoquinone pool.
复制标题
DOI：
10.1016/j.plaphy.2015.10.009
复制
发表时间：
2015-12
期刊：
影响因子：
--
通讯作者：
Verdiana Steccanella;M. Hansson;P. Jensen
中科院分区：
文献类型：
--
作者：
Verdiana Steccanella;M. Hansson;P. Jensen
叶绿素是光合作用中必不可少的辅因子。除了环化反应外，叶绿素途径的所有步骤都得到了很好的表征，在环化反应中，在镁原卟啉IX单甲酯转化为原叶绿素的过程中形成了叶绿素分子的第五环。到目前为止，该环化酶唯一的亚基是ACSF(大麦中为Xantha-L，拟南芥中为Chl27)。该亚基含有一个典型的双铁结合序列，属于双铁蛋白的一个亚群，如叶绿体中的叶绿体末端氧化酶(PTOX)和线粒体中的交替氧化酶(AOX)。为了完成催化循环，这些蛋白质的铁离子需要从Fe3+还原到Fe2+，并且需要还原酶或其他形式的还原剂。据报道，交替氧化酶(AOX)和叶绿体末端氧化酶(PTOX)分别利用双铁中心氧化泛喹酚和质体酚。在这篇论文中，我们使用了一种特异的双铁蛋白抑制剂以及影响光合作用电子流调节的拟南芥和大麦突变体，以证明环化步骤确实是直接耦合到质醌池中的。因此，胞质喹酚可能作为环酶反应的电子供体，从而发挥环酶还原酶的作用。这将在类囊体氧化还原状态和叶绿素的生物合成之间提供功能联系。
Chlorophylls are essential cofactors in photosynthesis. All steps in the chlorophyll pathway are well characterized except for the cyclase reaction in which the fifth ring of the chlorophyll molecule is formed during conversion of Mg-protoporphyrin IX monomethyl ester into Protochlorophyllide. The only subunit of the cyclase identified so far, is AcsF (Xantha-l in barley and Chl27 in Arabidopsis). This subunit contains a typical consensus di-iron-binding sequence and belongs to a subgroup of di-iron proteins, such as the plastid terminal oxidase (PTOX) in the chloroplast and the alternative oxidase (AOX) found in mitochondria. In order to complete the catalytic cycle, the irons of these proteins need to be reduced from Fe3+to Fe2+and either a reductase or another form of reductant is required. It has been reported that the alternative oxidase (AOX) and the plastid terminal oxidase (PTOX) utilize the di-iron center to oxidise ubiquinol and plastoquinol, respectively. In this paper, we have used a specific inhibitor of di-iron proteins as well as Arabidopsis and barley mutants affected in regulation of photosynthetic electron flow, to show that the cyclase step indeed is directly coupled to the plastoquinone pool. Thus, plastoquinol might act as an electron donor for the cyclase reaction and thereby fulfil the role of a cyclase reductase. That would provide a functional connection between the redox status of the thylakoids and the biosynthesis of chlorophyll.