Replacement of the methionine axial ligand to the primary electron acceptor A0 slows the A0- reoxidation dynamics in photosystem I.
Replacement of the methionine axial ligand to the primary electron acceptor A0 slows the A0- reoxidation dynamics in photosystem I.
复制标题
将甲硫氨酸轴向配体替换为主要电子受体 A0 会减慢光系统 I 中 A0-再氧化动力学。
DOI：
10.1016/j.bbabio.2006.12.013
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发表时间：
2007
期刊：
影响因子：
--
通讯作者：
A. Webber
中科院分区：
文献类型：
--
作者：
V. M. Ramesh;K. Gibasiewicz;Su Lin;S. Bingham;A. Webber
细长热聚球藻光系统I（PSI）的晶体结构显示出两个几乎对称的电子传递辅因子分支，包括主要电子供体P700和一系列电子受体A、A0和A1，它们与PsaA和PsaB异二聚体结合。每个推定的初级电子受体叶绿素，A0的中心镁原子，异常协调的硫原子的蛋氨酸688的PsaA和668的PsaB，分别。我们[Ramesh et al.（2004 a）Biochemistry 43：1369-1375]已经证明，在单细胞绿色衣藻的PSI中，用组氨酸替换甲硫氨酸会导致A0-的积累（在300 ps的时间尺度内），这表明PsaA和PsaB分支都是活性的。这与蓝藻PSI相反，其中用甲硫氨酸至亮氨酸突变体的研究表明，电子转移主要沿着PsaA分支发生。在这篇文章中，我们报告了甲硫氨酸变为亮氨酸或丝氨酸导致A 0 −在C的PSI的PsaA和PsaB分支上的类似积累。reinhardtii，正如我们之前报道的组氨酸突变体。更重要的是，我们进一步证明，对于所有研究中的突变体，A0−的积累是短暂的，A0−的再氧化发生在1-2 ns内，比野生型PSI慢两个数量级，最有可能是通过缓慢的电子转移到A1。这说明了一个不可或缺的作用，蛋氨酸作为一个轴向配体的主要受体A0在优化PSI的电荷稳定的速率。提出了该反应的一个简单的能量模型。我们的研究结果支持光系统I中沿着两个辅因子分支的等效电子转移模型。
The recent crystal structure of photosystem I (PSI) from Thermosynechococcus elongatus shows two nearly symmetric branches of electron transfer cofactors including the primary electron donor, P700, and a sequence of electron acceptors, A, A0and A1, bound to the PsaA and PsaB heterodimer. The central magnesium atoms of each of the putative primary electron acceptor chlorophylls, A0, are unusually coordinated by the sulfur atom of methionine 688 of PsaA and 668 of PsaB, respectively. We [Ramesh et al. (2004a) Biochemistry 43:1369–1375] have shown that the replacement of either methionine with histidine in the PSI of the unicellular green alga Chlamydomonas reinhardtii resulted in accumulation of A0−(in 300-ps time scale), suggesting that both the PsaA and PsaB branches are active. This is in contrast to cyanobacterial PSI where studies with methionine-to-leucine mutants show that electron transfer occurs predominantly along the PsaA branch. In this contribution we report that the change of methionine to either leucine or serine leads to a similar accumulation of A0−on both the PsaA and the PsaB branch of PSI from C. reinhardtii, as we reported earlier for histidine mutants. More importantly, we further demonstrate that for all the mutants under study, accumulation of A0−is transient, and that reoxidation of A0−occurs within 1–2 ns, two orders of magnitude slower than in wild type PSI, most likely via slow electron transfer to A1. This illustrates an indispensable role of methionine as an axial ligand to the primary acceptor A0in optimizing the rate of charge stabilization in PSI. A simple energetic model for this reaction is proposed. Our findings support the model of equivalent electron transfer along both cofactor branches in Photosystem I.
影响因子：
56.9
作者：
BOYNTON, JE;GILLHAM, NW;SANFORD, JC
通讯作者：
SANFORD, JC