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The tuning of electron and proton-coupled electron transfer reactions of solar water oxidation : pulsed magnetic resonance spectroscopy studies of photosystem ii.

机译：太阳水氧化的电子和质子耦合电子转移反应的调谐：光系统的脉冲磁共振波谱研究ii。

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摘要

In the photosynthetic reaction centers, Photosystem II (PSII) and Photosystem I (PSI), specific cofactors allow for the highly efficient electron and proton transfer through these proteins. While high-resolution X-ray crystal structures of both PSII and PSI have been published recently, there is limited information on the electronic structure of these charge-transfer cofactors. We have applied the magnetic resonance spectroscopy techniques of electron paramagnetic resonance (EPR) spectroscopy and solid state nuclear magnetic resonance (NMR) spectroscopy to the analysis of electron transport cofactors of photosynthetic reaction centers. The electronic and molecular structure of photosynthetic electron transport cofactors have been probed in two distinct effects 1) internal effects on structure through cofactor functional group substitution, and 2) external effects on structure through interaction with cofactor environment (electrostatics, pi-stacking, hydrogen bonding, hydrophobicity). A detailed description of the tuning of photosynthetic electron transport cofactors by their protein environments will help facilitate the design of more efficient, bio-inspired solar energy capture systems. The highly demanding reaction of water oxidation occurs at the donor-side of PSII. This reaction takes place at the tetranuclear manganese-calcium-oxo (Mn4-Ca-oxo) cluster that is facilitated by the proton-coupled electron transfer (PCET) reactions at a redox-active tyrosine residue (Y Z). PSII contains two symmetric tyrosine residues, YZ and YD, within the heterodimeric polypeptide core, which though chemically identical display very different redox and kinetic properties. On the donor-side of PSII, I use pulsed EPR on, 1) effects of the ligand environment and small molecule coordination on the electronic structure of the Mn4-Ca-oxo cluster and the proteinaceous model, manganese catalase, and 2) the electronic properties of the local environments of YZ and YD to obtain insight on the functional tuning of PCET reactions of these two redox-active tyrosine residues. On the acceptor side of PSII and in the cofactor chain of PSI, quinones function as electron transport cofactors. The versatility and functional diversity of quinone cofactors is primarily due to the diverse mid-point potentials that are tuned by the substituent effects and interactions with surrounding amino acids residues in their respective protein binding pockets. I demonstrate the use of pulsed EPR spectroscopy to describe: 1) an analysis of a library of substituted 1,4 naphthoquinone molecules to correlate the mid-point potentials with the electronic structure, 2) the effects of site-specific mutagenesis on the electron structure of the electron acceptor, QA, of PSII, and 3) the electronic structure of substituted neutral radical hydroquinones and their relation to the PCET reactions of photosynthetic chemical energy storage. I also demonstrate the analysis of a library of substituted benzoquinone molecules by solid-state NMR and demonstrate its potential use in determining quinone-protein interactions. From analysis of the interactions of electron and proton transport cofactors the interaction of these cofactors with their surrounding environments through hydrogen bonding has been highlighted as a key interaction. Unlike previous accounts on electron transport dependence purely on the strength or length of a hydrogen bond between cofactor and protein, these studies put in a new light the dependence on hydrogen bond partner angular orientation to one another as a key tuning factor in the electron and proton transfer reactions with photosynthetic reaction centers.
机译：在光合反应中心光系统II（PSII）和光系统I（PSI）中，特定的辅助因子可通过这些蛋白质进行高效的电子和质子转移。虽然最近已经发布了PSII和PSI的高分辨率X射线晶体结构，但是关于这些电荷转移辅助因子的电子结构的信息有限。我们已将电子顺磁共振（EPR）光谱和固态核磁共振（NMR）光谱的磁共振光谱技术应用于光合作用反应中心的电子传输辅助因子的分析。已探究了光合电子传递辅助因子的电子和分子结构，具有两种不同的作用：1）通过辅助因子官能团取代对结构的内部影响，以及2）通过与辅助因子环境的相互作用（静电，π堆积，氢键作用）对结构的外部影响，疏水性）。通过蛋白质环境调节光合作用电子转运辅因子的详细描述将有助于促进更有效的，受生物启发的太阳能捕获系统的设计。在PSII的供体侧发生了要求很高的水氧化反应。该反应在四核锰-钙-氧（Mn4-Ca-氧）簇上发生，这是由于在氧化还原活性酪氨酸残基（Y Z）上的质子偶联电子转移（PCET）反应所致。 PSII在异二聚体多肽核心中包含两个对称的酪氨酸残基YZ和YD，尽管化学上相同，但它们显示出非常不同的氧化还原和动力学性质。在PSII的供体方面，我使用脉冲EPR来进行以下研究：1）配体环境和小分子配位对Mn4-Ca-氧代簇和蛋白质模型，锰过氧化氢酶的电子结构的影响，以及2）电子YZ和YD局部环境的特性，以了解这两个氧化还原活性酪氨酸残基PCET反应的功能调节。在PSII的受体侧和PSI的辅助因子链中，醌起电子传输辅助因子的作用。醌辅因子的多功能性和功能多样性主要归因于中点电势的多样性，这些电势是通过取代基效应以及与它们各自蛋白质结合口袋中周围氨基酸残基的相互作用来调节的。我演示了使用脉冲EPR光谱学来描述：1）分析取代的1,4萘醌分子文库，以将中点电位与电子结构相关联； 2）特定位点诱变对电子结构的影响3）取代的中性自由基氢醌的电子结构及其与光合化学能存储的PCET反应的关系。我还展示了通过固态NMR对取代的苯醌分子库的分析，并展示了其在确定醌-蛋白质相互作用中的潜在用途。通过对电子和质子传输辅因子相互作用的分析，这些辅因子通过氢键与周围环境的相互作用被强调为关键相互作用。与以往关于电子传输依赖纯粹依赖于辅因子和蛋白质之间氢键的强度或长度的解释不同，这些研究以崭新的视角揭示了对氢键伴侣角取向的依赖性是电子和质子中的关键调节因子通过光合反应中心转移反应。

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  • 作者

    Coates, Christopher S.;

  • 作者单位

    Rensselaer Polytechnic Institute.;

  • 授予单位 Rensselaer Polytechnic Institute.;
  • 学科 Chemistry General.;Chemistry Inorganic.;Chemistry Physical.
  • 学位 Ph.D.
  • 年度 2013
  • 页码 436 p.
  • 总页数 436
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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