Faculty of Science, University of South Bohemia, Branisovska 1760, 370 05 Ceske Budejovice, Czech Republic.
J Chem Phys. 2022 May 7;156(17):175101. doi: 10.1063/5.0085141.
Metalloproteins, known to efficiently transfer electronic charge in biological systems, recently found their utilization in nanobiotechnological devices where the protein is placed into direct contact with metal surfaces. The feasibility of oxidation/reduction of the protein redox sites is affected by the reorganization free energies, one of the key parameters determining the transfer rates. While their values have been measured and computed for proteins in their native environments, i.e., in aqueous solution, the reorganization free energies of dry proteins or proteins adsorbed to metal surfaces remain unknown. Here, we investigate the redox properties of blue copper protein azurin, a prototypical redox-active metalloprotein previously probed by various experimental techniques both in solution and on metal/vacuum interfaces. We used a hybrid quantum mechanical/molecular mechanical computational technique based on density functional theory to explore protein dynamics, flexibility, and corresponding reorganization free energies in aqueous solution, vacuum, and on vacuum gold interfaces. Surprisingly, the reorganization free energy only slightly decreases when azurin is dried because the loss of the hydration shell leads to larger flexibility of the protein near its redox site. At the vacuum gold surfaces, the energetics of the structure relaxation depends on the adsorption geometry; however, significant reduction of the reorganization free energy was not observed. These findings have important consequences for the charge transport mechanism in vacuum devices, showing that the free energy barriers for protein oxidation remain significant even under ultra-high vacuum conditions.
金属蛋白酶在生物系统中有效地传递电子电荷，最近在纳米生物技术设备中得到了应用，其中蛋白质直接与金属表面接触。蛋白质氧化还原中心的氧化还原可行性受重组自由能的影响，重组自由能是决定转移速率的关键参数之一。虽然已经测量和计算了蛋白质在其天然环境（即水溶液）中的重组自由能，但干燥蛋白质或吸附在金属表面的蛋白质的重组自由能仍然未知。在这里，我们研究了蓝色铜蛋白天青蛋白的氧化还原性质，天青蛋白是一种典型的氧化还原活性金属蛋白酶，之前已经通过各种实验技术在溶液中和金属/真空界面上进行了探测。我们使用了一种基于密度泛函理论的混合量子力学/分子力学计算技术来探索水溶液、真空中以及真空金界面上天青蛋白的动力学、柔韧性和相应的重组自由能。令人惊讶的是，当天青蛋白干燥时，重组自由能仅略有下降，因为水合壳的损失导致其氧化还原部位附近的蛋白质具有更大的柔韧性。在真空金表面上，结构弛豫的能量取决于吸附几何形状；然而，没有观察到重组自由能的显著降低。这些发现对真空器件中的电荷传输机制有重要影响，表明即使在超高真空条件下，蛋白质氧化的自由能障碍仍然很大。
