Mutations in the CD-loop region of the D2 protein in Synechocystis sp. PCC 6803 modify charge recombination pathways in photosystem II in vivo.
Mutations in the CD-loop region of the D2 protein in Synechocystis sp. PCC 6803 modify charge recombination pathways in photosystem II in vivo.
复制标题
集胞藻 D2 蛋白 CD 环区域的突变。
DOI：
10.1021/bi001679m
复制
发表时间：
2000
期刊：
影响因子：
2.9
通讯作者：
Vermaas,WF
中科院分区：
文献类型：
--
作者：
Vavilin,DV;Vermaas,WF
光系统II的D2蛋白的内腔CD环区域含有与主要电子供体P680和氧化还原活性酪氨酰残基YD相互作用的残基。研究了集胞藻（Synechocystissp.）PCC 6803，其中大部分在D2蛋白的残基164−170、179−186或187−194处携带组合突变。为了便于表征突变体中的光系统II特性，将CD环突变引入光系统I较少的背景中。根据DCMU处理细胞的可变荧光衰减测量，大多数突变体中QA-与供体侧的电荷重组（t1/2= 45 - 140 ms）比对照（t1/2= 180 ms）更快。然而，在一个突变体（命名为C7-3）中，QA-的衰减比对照慢2倍（t1/2= 360 ms）。每个突变体的衰变半衰期与由于S2 QA-电荷重组而发射的热释光（TL）的Q带的产率相关。C7-3突变体具有最高的TL强度，而在快速QA衰减的突变体中没有检测到Q带（t1/2= 45 - 50 ms）。在这些菌株中的重组率和TL产量的相关变化表明，QA-和供体侧之间的电荷重组的非辐射途径的存在。这可能涉及从QA-到P680+的直接电子转移，而不会导致激发叶绿素的形成。CD环中的许多突变似乎在S2 QA状态的寿命期间增加平衡P680+浓度，例如，通过使P680+/P680氧化还原对的中点电位更负。非辐射电荷复合途径涉及一个低的活化能，是较少的温度依赖性比激发P680的形成，导致TL发射。因此，在这些突变体的TL测量期间，S2 QA状态可以在达到辐射电荷复合变得可行的温度之前非辐射地复合。本文的结果强调了两种电荷重组途径的存在以及D2蛋白的CD环在确定P680+ S1和P680 S2态之间的能隙中的重要性。
The lumenal CD-loop region of the D2 protein of photosystem II contains residues that interact with the primary electron donor P680 and the redox active tyrosyl residue YD. Photosystem II properties were studied in a number of photoautotrophic mutants ofSynechocystissp. PCC 6803, most of which carried combinatorial mutations in residues 164−170, 179−186, or 187−194 of the D2 protein. To facilitate characterization of photosystem II properties in the mutants, the CD-loop mutations were introduced into a photosystem I-less background. According to variable fluorescence decay measurements in DCMU-treated cells, charge recombination of QA-with the donor side was faster in the majority of mutants (t1/2= 45−140 ms) than in the control (t1/2= 180 ms). However, in one mutant (named C7-3), the decay of QA-was 2 times slower than in the control (t1/2= 360 ms). The decay half-time of each mutant correlated with the yield of the Q-band of thermoluminescence (TL) emitted due to S2QA-charge recombination. The C7-3 mutant had the highest TL intensity, whereas no Q-band was detected in the mutants with fast QA-decay (t1/2= 45−50 ms). The correlated changes in the rate of recombination and in TL yield in these strains suggest the existence of a nonradiative pathway of charge recombination between QA-and the donor side. This may involve direct electron transfer from QA-to P680+in a way not leading to formation of excited chlorophyll. Many mutations in the CD-loop appear to increase the equilibrium P680+concentration during the lifetime of the S2QA-state, for example, by making the midpoint potential of the P680+/P680 redox couple more negative. The nonradiative charge recombination pathway involves a low activation energy and is less temperature-dependent than the formation of excited P680 that leads to TL emission. Therefore, during the TL measurements in these mutants, the S2QA-state can recombine nonradiatively before temperatures are reached at which radiative charge recombination becomes feasible. The results presented here highlight the presence of two charge recombination pathways and the importance of the CD-loop of the D2 protein in determination of the energy gap between the P680+S1and P680S2states.