No evidence from FTIR difference spectroscopy that glutamate-189 of the D1 polypeptide ligates a Mn ion that undergoes oxidation during the S0 to S1, S1 to S2, or S2 to S3 transitions in photosystem II.
No evidence from FTIR difference spectroscopy that glutamate-189 of the D1 polypeptide ligates a Mn ion that undergoes oxidation during the S0 to S1, S1 to S2, or S2 to S3 transitions in photosystem II.
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FTIR 差异光谱没有证据表明 D1 多肽的谷氨酸 189 连接在光系统 II 中 S0 到 S1、S1 到 S2 或 S2 到 S3 转变过程中经历氧化的 Mn 离子。
DOI：
10.1021/bi060583a
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发表时间：
2006
期刊：
影响因子：
2.9
通讯作者：
Debus,RichardJ
中科院分区：
文献类型：
--
作者：
Strickler,MelodieA;Hillier,Warwick;Debus,RichardJ
在最近的X-射线晶体结构模型的光系统II，Glu 189的D1多肽被指定为配体的氧释放Mn 4集群。为了确定D1-Glu 189是否连接了在S 0 → S1、S1→ S2和S2→ S3的一个或多个转换过程中发生氧化的Mn离子，使用FTIR差谱对来自蓝细菌集胞藻的D1-E189 Q和D1-E189 R突变体PSII颗粒中的单个S态转换进行了研究。将PCC 6803与野生型PSII颗粒中的那些进行比较。值得注意的是，数据显示，两种突变都没有显著改变任何FTIR差谱的中频区域（1800 - 1200 cm-1）。重要的是，这两种突变都没有消除任何可能被分配给D1-Glu 189的特定对称或不对称羧酸伸缩模式。所观察到的小的光谱改变在幅度上与在已经通过不同方法交换到FTIR分析缓冲液中的野生型PSII颗粒中观察到的那些或在D2-H189 Q突变体PSII颗粒中观察到的那些（残基D2-His 189位于距离Mn 4簇>25 nm处并且接受来自Tyr YD的氢键）相似。在D1-Glu 189突变体中没有显著的突变诱导的光谱改变，表明Mn 4簇的氧化在S 0 → S1、S1→ S2或S2→ S3跃迁期间不改变D1-Glu 189的羧酸伸缩模式的频率。对这些数据的一种解释是，D1-Glu 189连接了一个Mn离子，在任何这些S态转变过程中，该Mn离子都不会增加其电荷或氧化态。然而，由于先前对D1-Asp 170得出了相同的结论，并且由于最近的X射线晶体结构模型将D1-Asp 170和D1-Glu 189指定为连接不同的Mn离子，这一解释要求：（1）在S1→ S2跃迁过程中，Mn 4簇上产生的额外正电荷位于与D1-的α-COO-基团连接的Mn离子上。（2）在S 0 → S1和S2→ S3跃迁过程中，Mn 4簇上正电荷的增加都集中在未被D1-Asp 170、D1-Glu 189或D1-Ala 344连接的Mn离子上。FTIR数据的另一种解释是D1-Glu 189不连接Mn 4簇。这一结论与早期的D1-Glu 189突变体的光谱分析是一致的，但需要在X射线晶体结构模型中D1-Glu 189与锰的接近度是在收集X射线衍射数据期间发生的Mn 4簇的辐射诱导还原的伪像。
In the recent X-ray crystallographic structural models of photosystem II, Glu189 of the D1 polypeptide is assigned as a ligand of the oxygen-evolving Mn4cluster. To determine if D1-Glu189 ligates a Mn ion that undergoes oxidation during one or more of the S0→ S1, S1→ S2, and S2→ S3transitions, the FTIR difference spectra of the individual S-state transitions in D1-E189Q and D1-E189R mutant PSII particles from the cyanobacteriumSynechocystissp. PCC 6803 were compared with those in wild-type PSII particles. Remarkably, the data show that neither mutation significantly alters the mid-frequency regions (1800−1200 cm-1) ofanyof the FTIR difference spectra. Importantly, neither mutation eliminates any specific symmetric or asymmetric carboxylate stretching mode that might have been assigned to D1-Glu189. The small spectral alterations thatareobserved are similar in amplitude to those that are observed in wild-type PSII particles that have been exchanged into FTIR analysis buffer by different methods or those that are observed in D2-H189Q mutant PSII particles (the residue D2-His189 is located >25 Å from the Mn4cluster and accepts a hydrogen bond from Tyr YD). The absence of significant mutation-induced spectral alterations in the D1-Glu189 mutants shows that the oxidation of the Mn4cluster does not alter the frequencies of the carboxylate stretching modes of D1-Glu189 during the S0→ S1, S1→ S2, or S2→ S3transitions. One explanation of these data is that D1-Glu189 ligates a Mn ion that does not increase its charge or oxidation state during any of these S-state transitions. However, because the same conclusion was reached previously for D1-Asp170, and because the recent X-ray crystallographic structural models assign D1-Asp170 and D1-Glu189 as ligating different Mn ions, this explanation requires that (1) the extra positive charge that develops on the Mn4cluster during the S1→ S2transition be localized on the Mn ion that is ligated by the α-COO-group of D1-Ala344 and (2) any increase in positive charge that develops on the Mn4cluster during the S0→ S1and S2→ S3transitions be localized on the one Mn ion that isnotligated by D1-Asp170, D1-Glu189, or D1-Ala344. An alternative explanation of the FTIR data is that D1-Glu189 doesnotligate the Mn4cluster. This conclusion would be consistent with earlier spectroscopic analyses of D1-Glu189 mutants, but would require that the proximity of D1-Glu189 to manganese in the X-ray crystallographic structural models be an artifact of the radiation-induced reduction of the Mn4cluster that occurred during the collection of the X-ray diffraction data.