Protein Dielectric Environment Modulates the Electron-Transfer Pathway in Photosynthetic Reaction Centers
Protein Dielectric Environment Modulates the Electron-Transfer Pathway in Photosynthetic Reaction Centers
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DOI：
10.1016/j.bpj.2012.09.027
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发表时间：
2012-11-07
影响因子：
3.4
通讯作者：
Lin, Su
中科院分区：
文献类型：
--
作者：
Guo, Zhi;Woodbury, Neal W.;Lin, Su
球形Rhodobacter sphaeroides光合反应中心M210位置的酪氨酸被天冬氨酸取代，从而产生了在野生型中未观察到的快速电荷重组途径。显然，最初形成的电荷分离态（特殊对P的阳离子和a侧细菌叶绿素H-A的阴离子）在形成后很快通过邻近的细菌叶绿素B-A的重组而迅速衰减。然后，电荷分离状态在数十皮秒内松弛，而复合则减慢到数百皮秒或纳秒的时间尺度。这种介电弛豫导致了B-A（-）吸收的随时间的蓝移，这可以通过瞬态吸光度测量来监测。蛋白质动力学似乎也调节了H-A和下一个电子载体Q(A)（一种泛醌）之间的电子转移。突变体中该反应的动力学是复杂的，需要两个动力学项，与这两个动力学项相关的光谱是不同的；在较短和较长的H-A到q (a)电子转移相之间观察到H-A基态漂白的红移。动力学似乎与ph无关，表明基态质子化/去质子化产生的静态非均质性的贡献可以忽略不计。基于P+BA-和P+HA-两种早期电荷分离态的能级，建立了一个动力学模型，其中这些态的能量被快速蛋白质介电弛豫调制，这反过来改变了反应的动力学复杂性和反应途径。
The replacement of tyrosine by aspartic acid at position M210 in the photosynthetic reaction center of Rhodobacter sphaeroides results in the generation of a fast charge recombination pathway that is not observed in the wild-type. Apparently, the initially formed charge-separated state (cation of the special pair, P, and anion of the A-side bacteriopheophytin, H-A) can decay rapidly via recombination through the neighboring bacteriochlorophyll (B-A) soon after formation. The charge-separated state then relaxes over tens of picoseconds and recombination slows to the hundreds-of-picoseconds or nanosecond timescale. This dielectric relaxation results in a time-dependent blue shift of B-A(-) absorption, which can be monitored using transient absorbance measurements. Protein dynamics also appear to modulate the electron transfer between H-A and the next electron carrier, Q(A) (a ubiquinone). The kinetics of this reaction are complex in the mutant, requiring two kinetic terms, and the spectra associated with the two terms are distinct; a red shift of the H-A ground-state bleaching is observed between the shorter and longer H-A-to-Q(A) electron-transfer phases. The kinetics appears to be pH-independent, suggesting a negligible contribution of static heterogeneity originating from protonation/deprotonation in the ground state. A dynamic model based on the energy levels of the two early charge-separated states, P+BA- and P+HA- , has been developed in which the energetics of these states is modulated by fast protein dielectric relaxations and this in turn alters both the kinetic complexity of the reaction and the reaction pathway.