Hydrogen bonds between nitrogen donors and the semiquinone in the Q(B) site of bacterial reaction centers.
Hydrogen bonds between nitrogen donors and the semiquinone in the Q(B) site of bacterial reaction centers.
复制标题
氮供体和细菌反应中心 Q(B) 位点的半醌之间的氢键。
DOI：
10.1021/ja104134e
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发表时间：
2010
影响因子：
15
通讯作者：
Dikanov,SergeiA
中科院分区：
文献类型：
--
作者：
Martin,Erik;Samoilova,RimmaI;Narasimhulu,KupalaV;Wraight,ColinA;Dikanov,SergeiA
球形红假单胞菌的光合作用反应中心具有相同的泛醌-10分子，作为初级(QA)和次级(QB)电子受体。用X-波段2D脉冲EPR谱(HYSCORE)研究了天然和15N均匀标记反应中心中QB位点半喹酮与来自局部蛋白质环境的氮素的相互作用。QB半喹酮的14N和15N HYSCORE谱表明它们与带有转移未配对自旋密度的两个氮原子相互作用。由14N HYSCORE谱估算的四极偶合常数表明它们是咪唑残基的质子化氮和肽基酰胺氮。15N HYSCORE谱可以估计与这些氮的各向同性和各向异性偶联。根据这些数据，我们计算了转移到氮的2s和2p轨道上的未配对自旋密度，并分析了不同因素对各向异性超精细张量的贡献。其他蛋白质氮与半喹酮的超精细偶联很弱(<；0.1 MHz)。这些结果清楚地表明QB半喹酮与两个氮素形成氢键，并提供了与这些氮素的超精细偶联的定量特征，可用于QB位的理论模拟。根据四极耦合常数，一个氮只能分配到His-L190的Nδ上，这与所有现有的结构一致。然而，我们不能在两个候选者之间指定对应于第二个氮的残留物。使用多频光谱方法或选择性同位素标记的进一步工作将是明确分配这种氮的理想方法。
Photosynthetic reaction centers from Rhodobacter sphaeroides have identical ubiquinone-10 molecules functioning as primary (QA) and secondary (QB) electron acceptors. X-band 2D pulsed EPR spectroscopy, called HYSCORE, was applied to study the interaction of the QBsite semiquinone with nitrogens from the local protein environment in natural and15N uniformly labeled reactions centers.14N and15N HYSCORE spectra of the QBsemiquinone show the interaction with two nitrogens carrying transferred unpaired spin density. Quadrupole coupling constants estimated from14N HYSCORE spectra indicate them to be a protonated nitrogen of an imidazole residue and amide nitrogen of a peptide group.15N HYSCORE spectra allowed estimation of the isotropic and anisotropic couplings with these nitrogens. From these data, we calculated the unpaired spin density transferred onto 2s and 2p orbitals of nitrogen and analyzed the contribution of different factors to the anisotropic hyperfine tensors. The hyperfine coupling of other protein nitrogens with the semiquinone is weak (<0.1 MHz). These results clearly indicate that the QBsemiquinone forms hydrogen bonds withtwonitrogens and provide quantitative characteristics of the hyperfine couplings with these nitrogens, which can be used in theoretical modeling of the QBsite. On the basis of the quadrupole coupling constant, one nitrogen can only be assigned to Nδof His-L190, consistent with all existing structures. However, we cannot specify between two candidates the residue corresponding to the second nitrogen. Further work employing multifrequency spectroscopic approaches or selective isotope labeling would be desirable for unambiguous assignment of this nitrogen.