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首页> 外文期刊>Biochemistry >An Isotope-Edited FTIR Investigation of the Role of Ser-L223 in Binding Quinone (Q_B) and Semiquinone (Q_B~-) in the Reaction Center from Rhodobacter sphaeroides
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An Isotope-Edited FTIR Investigation of the Role of Ser-L223 in Binding Quinone (Q_B) and Semiquinone (Q_B~-) in the Reaction Center from Rhodobacter sphaeroides

机译：同位素编辑的FTIR研究球形红球菌反应中心中Ser-L223在结合醌（Q_B）和半醌（Q_B〜-）中的作用

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摘要

In the photosynthetic reaction center (RC) from the purple bacterium Rhodobacter sphaeroides,proton-coupled electron-transfer reactions occur at the secondary quinone (Q_B) site.Several nearby residues are important for both binding and redox chemistry involved in the light-induced conversion from Q_B to quinol Q_BH_2.Ser-L223 is one of the functionally important residues located near Q_B.To obtain information on the interaction between Ser-L223 and Q_B and Q_B,isotope-edited Q_B~-/Q_B FTIR difference spectra were measured in a mutant RC in which Ser-L223 is replaced with Ala and compared to the native RC.The isotope-edited IR fingerprint spectra for the C=O (C-O) and C=C (C-C) modes of Q_B (Q_B~-) in the mutant are essentially the same as those of the native RC.These findings indicate that highly equivalent interactions of Q_B and Q_B~- with the protein occur in both native and mutant RCs.The simplest explanation of these results is that Ser-L223 is not hydrogen bonded to Q_B or Q_B~- but presumably forms a hydrogen bond to a nearby acid group,preferentially Asp-L213.The rotation of the Ser OH proton from Asp-L213 to Q_B~- is expected to be an important step in the proton transfer to the reduced quinone.In addition,the reduced quinone remains firmly bound,indicating that other distinct hydrogen bonds are more important for stabilizing Q_B~-.Implications on the design features of the Q_B binding site are discussed.
机译：在紫色细菌球形红细菌（Rhodobacter sphaeroides）的光合作用反应中心（RC）中，质子偶联的电子转移反应发生在次级醌（Q_B）位点上。附近的几个残基对于光诱导转化涉及的结合和氧化还原化学都非常重要。从Q_B到喹啉Q_BH_2.Ser-L223是位于Q_B附近的重要功能残基之一。为了获得有关Ser-L223与Q_B和Q_B相互作用的信息，通过同位素分析Q_B〜-/ Q_B FTIR谱图突变的RC，其中Ser-L223被Ala取代并与天然RC进行了比较。在Q_B（Q_B〜-）的C = O（CO）和C = C（CC）模式下，同位素编辑的IR指纹图谱这些发现表明Q_B和Q_B〜-与蛋白质的等效相互作用在天然RC和突变RC中都存在，最简单的解释是Ser-L223不是氢绑定到Q_B或Q_B〜-但可能会与附近的酸基（优选为Asp-L213）形成氢键.Ser OH质子从Asp-L213旋转到Q_B〜-有望成为质子转移至还原醌的重要步骤。 ，还原的醌保持牢固的结合，表明其他独特的氢键对于稳定Q_B〜-更为重要。讨论了对Q_B结合位点设计特征的意义。

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