Proton release due to manganese binding and oxidation in modified bacterial reaction centers.
Proton release due to manganese binding and oxidation in modified bacterial reaction centers.
复制标题
由于锰在改良的细菌反应中心结合和氧化而释放质子。
作者：
L. Kálmán;M. Thielges;J. Williams;J. P. Allen
通过明减暗光学差光谱和质子吸收/释放的直接测量来表征具有设计的金属结合位点的高氧化反应中心中 Mn2+ 的结合和氧化的 pH 依赖性。这些突变体结合 Mn2+ 离子，可以有效地将电子转移到氧化的细菌叶绿素二聚体，如前所述 [Thielges 等人。 (2005) 生物化学 44, 7389-7394]。解离常数 KD 随着 pH 值的降低而显着增加。 KD 在 pH 7 和 pH 8 之间的 pH 依赖性与通过两个质子的静电释放而稳定的 Mn2+ 结合一致。质子释放对 Mn2+ 结合的 pH 依赖性很强，每个反应中心最大释放 1.4 H+，这被解释为配位残基和可能的其他附近残基的 pKa 值变化的结果。在光照下观察到与 Mn2+ 氧化相关的少量质子释放。这些结果表明，在考虑配体的金属配位和质子化状态的情况下，功能性金属结合位点可以整合到蛋白质中。
The pH dependence of binding and oxidation of Mn2+ in highly oxidizing reaction centers with designed metal-binding sites was characterized by light-minus-dark optical difference spectroscopy and direct measurements of proton uptake/release. These mutants bind a Mn2+ ion that can efficiently transfer an electron to the oxidized bacteriochlorophyll dimer, as described earlier [Thielges et al. (2005) Biochemistry 44, 7389-7394]. The dissociation constant, KD, significantly increased with decreasing pH. The pH dependence of KD between pH 7 and pH 8 was consistent with the binding of Mn2+ being stabilized by the electrostatic release of two protons. The strong pH dependence of proton release upon Mn2+ binding, with a maximal release of 1.4 H+ per reaction center, was interpreted as being a result of a shift in the pKa values of the coordinating residues and possibly other nearby residues. A small amount of proton release associated with Mn2+ oxidation was observed upon illumination. These results show that functional metal-binding sites can be incorporated into proteins upon consideration of both the metal coordination and protonation states of the ligands.