Departamento de Química Inorgánica, Analítica y Química Física, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Universitaria, Pab. 2, piso 1, C1428EHA-Buenos Aires, Argentina.
J Am Chem Soc. 2013 Mar 20;135(11):4389-97. doi: 10.1021/ja311786b. Epub 2013 Mar 12.
We have employed a combination of protein film voltammetry, time-resolved vibrational spectroelectrochemistry and molecular dynamics simulations to evaluate the electron-transfer reorganization free energy (λ) of cytochrome c (Cyt) in electrostatic complexes that mimic some basic features of protein-protein and protein-lipid interactions. The results reveal the existence of two native-like conformations of Cyt that present significantly different λ values. Conversion from the high to the low λ forms is triggered by electrostatic interactions, and involves the rupture of a weak H-bond between first- (M80) and second-sphere (Y67) ligands of the heme iron, as a distinctive feature of the conformational switch. The two flexible Ω loops operate as transducers of the electrostatic signal. This fine-tuning effect is abolished in the Y67F Cyt mutant, which presents a λ value similar to the WT protein in electrostatic complexes. We propose that interactions of Cyt with the natural redox partner proteins activate a similar mechanism to minimize the reorganization energy of interprotein electron transfer.
我们采用蛋白质膜伏安法、时间分辨振动光谱电化学和分子动力学模拟相结合的方法，评估了模拟蛋白质-蛋白质和蛋白质-脂质相互作用基本特征的静电复合物中细胞色素 c（Cyt）的电子转移重组自由能（λ）。结果表明 Cyt 存在两种具有相似 native-like 构象的形式，它们呈现出显著不同的 λ 值。从高 λ 形式向低 λ 形式的转变是由静电相互作用触发的，涉及到原卟啉环铁（M80）和第二配位体（Y67）之间弱氢键的断裂，这是构象开关的一个显著特征。两个灵活的 Ω 环作为静电信号的传感器。在 Y67F Cyt 突变体中，这种微调效应被消除，其 λ 值与静电复合物中的 WT 蛋白相似。我们提出，Cyt 与天然氧化还原伴侣蛋白的相互作用激活了类似的机制，以最小化蛋白质间电子转移的重组能。
