Department of Chemistry and Biochemistry, Baylor University, Waco, TX, USA.
Angew Chem Int Ed Engl. 2020 Jun 26;59(27):10989-10995. doi: 10.1002/anie.202001452. Epub 2020 Apr 28.
The degree by which metalloproteins partially regulate net charge (Z) upon electron transfer (ET) was recently measured for the first time using "protein charge ladders" of azurin, cytochrome c, and myoglobin [Angew. Chem. Int. Ed. 2018, 57(19), 5364-5368; Angew. Chem. 2018, 130, 5462-5466]. Here, we show that Cu, Zn superoxide dismutase (SOD1) is unique among proteins in its ability to resist changes in net charge upon single ET (e.g., ΔZ =0.05±0.08 per electron, compared to ΔZ =1.19±0.02). This total regulation of net charge by SOD1 is attributed to the protonation of the bridging histidine upon copper reduction, yielding redox centers that are isoelectric at both copper oxidation states. Charge regulation by SOD1 would prevent long range coulombic perturbations to residue pK 's upon ET at copper, allowing SOD1's "electrostatic loop" to attract superoxide with equal affinity (at both redox states of copper) during diffusion-limited reduction and oxidation of superoxide.
最近，首次使用天青蛋白、细胞色素 c 和肌红蛋白的“蛋白质电荷梯”来测量金属蛋白在电子转移（ET）过程中对净电荷（Z）的部分调节程度[Angew. Chem. Int. Ed. 2018, 57(19), 5364-5368; Angew. Chem. 2018, 130, 5462-5466]。在这里，我们发现铜锌超氧化物歧化酶（SOD1）在单个 ET 时抵抗净电荷变化的能力在蛋白质中是独一无二的（例如，每电子变化 0.05±0.08，而变化 1.19±0.02）。SOD1 对净电荷的这种完全调节归因于铜还原时桥连组氨酸的质子化，生成在两种铜氧化态下等电的氧化还原中心。SOD1 的电荷调节可以防止 ET 时铜上残基 pK '的长程库仑微扰，从而使 SOD1 的“静电环”在超氧化物的扩散限制还原和氧化过程中以相同的亲和力（在铜的两种氧化态下）吸引超氧化物。
