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Mutation H(M202)L does not lead to the formation of a heterodimer of the primary electron donor in reaction centers of Rhodobacter sphaeroides when combined with mutation I(M206)H.
Photosynthesis Research ( IF 3.7 ) Pub Date : 2020-03-03 , DOI: 10.1007/s11120-020-00728-9
Anton M Khristin 1 , Alexey A Zabelin 1 , Tatiana Yu Fufina 1 , Ravil A Khatypov 1 , Ivan I Proskuryakov 1 , Vladimir A Shuvalov 1 , Anatoly Ya Shkuropatov 1 , Lyudmila G Vasilieva 1
Affiliation  

In photosynthetic reaction centers (RCs) of purple bacteria, conserved histidine residues [His L173 and His M202 in Rhodobacter (Rba.) sphaeroides] are known to serve as fifth axial ligands to the central Mg atom of the bacteriochlorophyll (BChl) molecules (PA and PB, respectively) that constitute the homodimer (BChl/BChl) primary electron donor P. In a number of previous studies, it has been found that replacing these residues with leucine, which cannot serve as a ligand to the Mg ion of BChl, leads to the assembly of heterodimer RCs with P represented by the BChl/BPheo pair. Here, we show that a homodimer P is assembled in Rba. sphaeroides RCs if the mutation H(M202)L is combined with the mutation of isoleucine to histidine at position M206 located in the immediate vicinity of PB. The resulting mutant H(M202)L/I(M206)H RCs are characterized using pigment analysis, redox titration, and a number of spectroscopic methods. It is shown that, compared to wild-type RCs, the double mutation causes significant changes in the absorption spectrum of the P homodimer and the electronic structure of the radical cation P+, but has only minor effect on the pigment composition, the P/P+ midpoint potential, and the initial electron-transfer reaction. The results are discussed in terms of the nature of the axial ligand to the Mg of PB in mutant H(M202)L/I(M206)H RCs and the possibility of His M202 participation in the previously proposed through-bond route for electron transfer from the excited state P* to the monomeric BChl BA in wild-type RCs.



中文翻译:

当与突变 I(M206)H 结合时,突变 H(M202)L 不会导致在球形红细菌的反应中心形成初级电子供体的异二聚体。

在光合反应中心紫细菌(RCS),保守的组氨酸残基[他L173和His M202在红细菌是Rba。 假单胞菌是已知的,作为第五轴向配体与细菌叶绿素(BCHL)分子的中心的Mg原子](P A和 P B ),它们构成同型二聚体 (BChl/BChl) 主要电子供体 P。在之前的许多研究中,已经发现用亮氨酸代替这些残基,亮氨酸不能作为 Mg 离子的配体BChl 导致异二聚体 RC 的组装,其中 P 由 BChl/BPheo 对表示。在这里,我们展示了在Rba 中组装的同型二聚体 P。球状体如果突变 H(M202)L 与位于紧邻 P B 的位置 M206 处异亮氨酸突变为组氨酸结合,则为 RC 。由此产生的突变 H(M2O2)L/​​I(M2O6)H RC 使用色素分析、氧化还原滴定和许多光谱方法进行表征。结果表明,与野生型 RCs 相比,双突变导致 P 同源二聚体的吸收光谱和自由基阳离子 P +的电子结构发生显着变化,但对色素成分 P/ P +中点电位,以及初始电子转移反应。结果根据 P B的 Mg 的轴向配体的性质进行讨论在突变体 H(M202)L/I(M206)H RC 中,以及 His M202 参与先前提出的通过键合途径将电子从激发态 P* 转移到野生型 RC 中的单体 BChl B A 的可能性。

更新日期:2020-03-03
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