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首页> 外文期刊>Biochemistry >Functional analysis of combinatorialmutans withchanges in the C-terminus of the CD loop of the D2 proteinin photosystem II of synechocystis sp.PCC 6803
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Functional analysis of combinatorialmutans withchanges in the C-terminus of the CD loop of the D2 proteinin photosystem II of synechocystis sp.PCC 6803

机译：变囊藻（PCC 6803）光系统II中D2蛋白CD环C末端变化的组合变体功能分析

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Photosystem II properties were investigated in a set of combinatorial mutants containing changes in the C-terminal end of the CD lumenal loop (Glyl 87—Asn 194) in the D2 protein of Synechocystis sp. PCC 6803. Initial screening of variable fluorescence (F~) induction and decay in the presence of DCMU showed that all but one of the combinatorial strains tested had an increased rate of QA reoxidation. Two strains showed an increase in the amplitude of constant fluorescence (F0). Examination of the primary sequence of the combinatorial strains combined with results obtained from analysis of site-directed mutants suggested that alterations in residue 191 of D2 increased the rate of charge recombination. Indeed, reintroduction of Trpl9l, the residue present in wild type, slowed the QA reoxidation rate in the presence of DCMU by 2—3-fold. However, the nature of other residues, in particular at codon 192, was also important in determining charge recombination rates. The increase in F0 yield was due to an increased fluorescence lifetime of open reaction centers in intact cells and may reflect a decreased excitation trapping rate in the reaction center. This change was reversed by reintroduction of Trp 191 even though a mutant lacking just Trpl9l was normal in this respect. Trapping efficiency therefore was decreased only when multiple changes were present at the same time. We interpret Trpl9 1 and neighboring residues to influence the midpoint redox potential of P680/P680~ and in certain sequence contexts to affect the energy trapping efficiency by P680. The stability or environment of YDOX was essentially unaffected in the mutants. Interestingly, many combinatorial mutants displayed an increased requirement for chloride for photoautotrophic growth, and two mutants, C8-10 and C8-23, also required more calcium. This indicates that this CD loop region of D2 not only affects properties of P680 but also affects properties of the oxygen-evolving complex.
机译：在一组组合突变体中研究了光系统II的性质，该组合突变体包含集胞藻属（Synechocystis sp。）D2蛋白中CD管腔环（Glyl 87-Asn 194）C末端的变化。 PCC6803。在存在DCMU的情况下，对可变荧光（F〜）诱导和衰变的初步筛选显示，除一种组合菌株外，所有菌株均具有提高的QA重氧化速率。两个菌株显示恒定荧光（F0）的幅度增加。检查组合菌株的一级序列，并结合定点突变体的分析结果表明，D2残基191的改变增加了电荷重组的速率。实际上，在野生型中存在的残基Trp1191的重新引入使存在DCMU的QA重氧化速度降低了2-3倍。然而，其他残基的性质，特别是192号密码子，对确定电荷重组率也很重要。 F0产量的增加是由于完整细胞中开放反应中心的荧光寿命增加，并且可能反映了反应中心中激发捕获速率的降低。即使在这方面仅缺少Trp1191的突变体是正常的，该变化也通过重新引入Trp 191而被逆转。因此，仅当同时存在多个更改时，陷印效率才降低。我们解释Trpl9 1和附近的残基会影响P680 / P680〜的中点氧化还原电势，并在某些序列背景下影响P680的能量捕获效率。 YDOX的稳定性或环境在突变体中基本不受影响。有趣的是，许多组合突变体显示出氯化碳对光养植物生长的需求增加，而两个突变体C8-10和C8-23也需要更多的钙。这表明D2的该CD环区域不仅影响P680的性质，而且影响析氧配合物的性质。

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