Department of Analytic and Bioinorganic Chemistry, University of Copenhagen, 2100 Copenhagen, Denmark.
Proc Natl Acad Sci U S A. 2013 Jun 25;110(26):10536-40. doi: 10.1073/pnas.1215081110. Epub 2013 Jun 12.
Low reorganization free energies are necessary for fast electron transfer (ET) reactions. Hence, rational design of redox proteins with lower reorganization free energies has been a long-standing challenge, promising to yield a deeper understanding of the underlying principles of ET reactivity and to enable potential applications in different energy conversion systems. Herein we report studies of the intramolecular ET from pulse radiolytically produced disulfide radicals to Cu(II) in rationally designed azurin mutants. In these mutants, the copper coordination sphere has been fine-tuned to span a wide range of reduction potentials while leaving the metal binding site effectively undisrupted. We find that the reorganization free energies of ET within the mutants are indeed lower than that of WT azurin, increasing the intramolecular ET rate constants almost 10-fold: changes that are correlated with increased flexibility of their copper sites. Moreover, the lower reorganization free energy results in the ET rate constants reaching a maximum value at higher driving forces, as predicted by the Marcus theory.
低重组自由能对于快速电子转移（ET）反应是必要的。因此，合理设计具有更低重组自由能的氧化还原蛋白一直是一个长期存在的挑战，有望深入了解 ET 反应的基本原理，并为不同的能量转换系统中的潜在应用提供可能性。本文报告了通过脉冲辐解产生的二硫自由基到铜（II）在合理设计的蓝铜蛋白突变体中的分子内 ET 的研究。在这些突变体中，铜配位球精细调谐以跨越广泛的还原电势范围，同时有效地不破坏金属结合位点。我们发现突变体中的 ET 重组自由能确实低于 WT 蓝铜蛋白，将分子内 ET 速率常数提高近 10 倍：这与它们的铜位点的增加的灵活性相关。此外，较低的重组自由能导致 ET 速率常数在更高的驱动力下达到最大值，正如马库斯理论所预测的那样。
