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首页> 外文期刊>Biochemistry >Q-Band Electron-Nuclear Double Resonance Reveals Out-of-Plane Hydrogen Bonds Stabilize an Anionic Ubisemiquinone in Cytochrome bo(3) from Escherichia coli
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Q-Band Electron-Nuclear Double Resonance Reveals Out-of-Plane Hydrogen Bonds Stabilize an Anionic Ubisemiquinone in Cytochrome bo(3) from Escherichia coli

机译：Q波段电子核双共振揭示出平面外氢键稳定从大肠杆菌（Escherichia coli）的细胞色素bo（3）中的阴离子泛素半醌。

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摘要

The respiratory cytochrome bo(3) ubiquinol oxidase from Escherichia coli has a high-affinity ubiquinone binding site that stabilizes the one-electron reduced ubisemiquinone (SQ(H)), which is a transient intermediate during the electron-mediated reduction of O-2 to water. It is known that SQ(H) is stabilized by two strong hydrogen bonds from R71 and D75 to ubiquinone carbonyl oxygen O1 and weak hydrogen bonds from H98 and Q101 to O4. In this work, SQ(H) was investigated with orientation-selective Q-band (similar to 34 GHz) pulsed H-1 electron-nuclear double resonance (ENDOR) spectroscopy on fully deuterated cytochrome (cyt) bo(3) in a H2O solvent so that only exchangeable protons contribute to the observed ENDOR spectra. Simulations of the experimental ENDOR spectra provided the principal values and directions of the hyperfine (hfi) tensors for the two strongly coupled H-bond protons (H1 and H2). For H1, the largest principal component of the proton anisotropic hfi tensor T-z' = 11.8 MHz, whereas for H2, T-z' = 8.6 MHz. Remarkably, the data show that the direction of the H1 H-bond is nearly perpendicular to the quinone plane (similar to 70 degrees out of plane). The orientation of the second strong hydrogen bond, H2, is out of plane by similar to 25 degrees. Equilibrium molecular dynamics simulations on a membrane-embedded model of the cyt bo(3) Q(H) site show that these H-bond orientations are plausible but do not distinguish which H-bond, from R71 or D75, is nearly perpendicular to the quinone ring. Density functional theory calculations support the idea that the distances and geometries of the H-bonds to the ubiquinone carbonyl oxygens, along with the measured proton anisotropic hfi couplings, are most compatible with an anionic (deprotonated) ubisemiquinone.
机译：大肠杆菌的呼吸细胞色素bo（3）泛醇氧化酶具有高亲和力的泛醌结合位点，可稳定单电子还原的泛半醌（SQ（H）），这是电子介导的O-2还原过程中的过渡中间体浇水。已知SQ（H）由R71和D75到泛醌羰基氧O1的两个强氢键和H98和Q101到O4的弱氢键稳定。在这项工作中，SQ（H）用定向选择性Q波段（类似于34 GHz）在H2O中完全氘化的细胞色素（cyt）bo（3）上进行了脉冲H-1电子核双共振（ENDOR）光谱研究溶剂，因此只有可交换的质子有助于观察到的ENDOR光谱。 ENDOR实验光谱的仿真提供了两个强耦合H键质子（H1和H2）的超精细（hfi）张量的主要值和方向。对于H1，质子各向异性hfi张量的最大主分量T-z'= 11.8 MHz，而对于H2，T-z'= 8.6 MHz。值得注意的是，数据显示H1 H键的方向几乎垂直于醌平面（近似于平面70度）。第二个强氢键H2的方向偏离平面约25度。在cyt bo（3）Q（H）位点的膜嵌入模型上进行的平衡分子动力学模拟显示，这些H键方向是合理的，但不能区分R71或D75中哪个H键几乎垂直于H键。醌环。密度泛函理论计算支持以下想法：氢键与泛醌羰基氧的距离和几何形状以及测得的质子各向异性hfi偶合与阴离子（去质子化的）泛半醌最相容。

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