X-ray crystal structure of the light-independent protochlorophyllide reductase
X-ray crystal structure of the light-independent protochlorophyllide reductase
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DOI：
10.1038/nature08950
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发表时间：
2010-05-06
期刊：
影响因子：
64.8
通讯作者：
Fujita, Yuichi
中科院分区：
文献类型：
--
作者：
Muraki, Norifumi;Nomata, Jiro;Fujita, Yuichi
光合生物采用两种不同的策略来还原原叶绿素（Pchlide）的C17=C18双键以形成叶绿素a的直接前体叶绿素a（参考文献1-4）。第一个涉及光依赖性Pchlide氧化还原酶的活性（5-9），第二个涉及光非依赖性（暗操作）Pchlide氧化还原酶（10）（DPOR）。DPOR是一种固氮酶样酶，由两种组分组成，L-蛋白（BchL二聚体）和NB-蛋白（BchN-BchB异源四聚体），它们在结构上分别与固氮酶Fe蛋白和MoFe蛋白相关（10，11）。在这里，我们报告的NB-蛋白质的DPOR从红细菌capsulatus在2.3埃的分辨率的晶体结构。正如预期的那样，整体结构与固氮酶MoFe蛋白的结构相似：每个催化BchN-BchB单元包含一个Pchlide和一个由一个天冬氨酸和三个半胱氨酸唯一配位的铁硫簇（NB簇）。独特的天冬氨酸连接对于簇组装不是必需的，但对于催化活性是必需的。特异性Pchlide结合伴随着属于下一个催化BchN-BchB单元的α-螺旋的部分解旋。我们提出了一个独特的反式特异性还原机制，其中扭曲的C17-丙酸Pchlide和天冬氨酸BchB作为质子供体C18和C17 Pchlide，分别。有趣的是，NB-簇和Pchlide的空间排列几乎与固氮酶MoFe-蛋白中的P-簇和FeMo-辅因子的空间排列相同，说明存在共同的结构以减少卟啉和二氮的化学稳定的多键。
Photosynthetic organisms adopt two different strategies for the reduction of the C17=C18 double bond of protochlorophyllide (Pchlide) to form chlorophyllide a, the direct precursor of chlorophyll a (refs 1-4). The first involves the activity of the light-dependent Pchlide oxidoreductase(5-9), and the second involves the light-independent (dark-operative) Pchlide oxidoreductase(10) (DPOR). DPOR is a nitrogenase-like enzyme consisting of two components, L-protein (a BchL dimer) and NB-protein (a BchN-BchB heterotetramer), which are structurally related to nitrogenase Fe protein and MoFe protein, respectively(10,11). Here we report the crystal structure of the NB-protein of DPOR from Rhodobacter capsulatus at a resolution of 2.3 angstrom. As expected, the overall structure is similar to that of nitrogenase MoFe protein: each catalytic BchN-BchB unit contains one Pchlide and one iron-sulphur cluster (NB-cluster) coordinated uniquely by one aspartate and three cysteines. Unique aspartate ligation is not necessarily needed for the cluster assembly but is essential for the catalytic activity. Specific Pchlide-binding accompanies the partial unwinding of an a-helix that belongs to the next catalytic BchN-BchB unit. We propose a unique trans-specific reduction mechanism in which the distorted C17-propionate of Pchlide and an aspartate from BchB serve as proton donors for C18 and C17 of Pchlide, respectively. Intriguingly, the spatial arrangement of the NB-cluster and Pchlide is almost identical to that of the P-cluster and FeMo-cofactor in nitrogenase MoFe-protein, illustrating that a common architecture exists to reduce chemically stable multibonds of porphyrin and dinitrogen.