Department of Chemistry and Biochemistry, Baylor University, Waco, TX, USA.
Phys Chem Chem Phys. 2024 Sep 11;26(35):22870-22881. doi: 10.1039/d4cp01989j.
Distinguishing proton-coupled electron transfer (PCET) from uncoupled electron transfer (ET) in proteins can be challenging. A recent investigation [J. C. Koone, M. Simmang, D. L. Saenger, M. L. Hunsicker-Wang and B. F. Shaw, , , 16488-16497] reported that protein charge ladders and capillary electrophoresis can distinguish between single ET, PCET, and two-proton coupled ET (2PCET) by directly measuring the change in protein net charge upon reduction/oxidation (Δ). The current study used similar methods to assess PCET in zinc-free, "double copper" superoxide dismutase-1 (4Cu-SOD1), where one copper is bound at the copper site of each monomer and one copper is bound at the bridging zinc site, resulting in a quasi-type III Cu center. At pH 7.4, the net charge () of the 4Cu-SOD1 dimer was unaffected by reduction of all four Cu ions, , Δ = -0.09 ± 0.05 per dimer (-0.02 ± 0.01 per copper atom). These values suggest that PCET is taking place at all four Cu atoms of the homodimer. Molecular dynamics and Poisson-Boltzmann calculations suggest that a metal-coordinating histidine at the zinc site (His71) is the proton acceptor. These data show how ligands of a naturally occurring zinc site can help facilitate PCET when the right redox metal is bound.
区分蛋白质中的质子耦合电子转移 (PCET) 和非耦合电子转移 (ET) 可能具有挑战性。最近的一项研究[J. C. Koone、M. Simmang、D. L. Saenger、M. L. Hunsicker-Wang 和 B. F. Shaw，，，16488-16497]报道称，蛋白质电荷梯和毛细管电泳可以通过直接测量还原/氧化过程中蛋白质净电荷的变化 (Δ) 来区分单 ET、PCET 和双质子耦合 ET (2PCET)。本研究使用类似的方法评估了锌缺失的“双铜”超氧化物歧化酶-1 (4Cu-SOD1) 中的 PCET，其中一个铜结合在每个单体的铜位点，一个铜结合在桥接锌位点，形成准 III 型 Cu 中心。在 pH 7.4 时，4Cu-SOD1 二聚体的净电荷 () 不受所有四个 Cu 离子还原的影响，Δ=-0.09 ± 0.05 每二聚体 (-0.02 ± 0.01 每个铜原子)。这些值表明 PCET 发生在同二聚体的所有四个 Cu 原子上。分子动力学和泊松-玻尔兹曼计算表明，锌位上一个与金属配位的组氨酸 (His71) 是质子受体。这些数据表明，当结合正确的氧化还原金属时，天然锌位的配体如何帮助促进 PCET。
