Cytochrome P450 enzymes play a pivotal role in biosynthetic and metabolic transformations. Especially, cytochrome P450 reductase (CPR) acts as the key electron donor for the oxygen activation by P450 monoxygenases, but the electron transfer mechanism within CPR is largely elusive. Here, extensive molecular dynamics (MD) and quantum mechanics/molecular mechanics (QM/MM) calculations were performed to elucidate CPR’s electron transfer mechanism. We found that electron transfer from FADH^– to FMN occurs through a proton-coupled electron transfer (PCET) mechanism. Here, Glu142 transfers a proton to FMN via a two-water-molecule chain, concurrent with electron transfer from FADH^– to FMN. The subsequent ET from FADH• to FMNH• involves an Asp675-mediated PCET process, where the Ser457-assisted proton transfer from FADH• to Asp675 is coupled with electron transfer from FADH• to FMNH•. Notably, the local electric field from the doubly protonated His180 significantly enhances the PCET reactions both kinetically and thermodynamically. This study highlights the vital role of the local electric field in facilitating biological electron transfer for enzymatic reactions.

中文翻译：

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局部电场驱动细胞色素 P450 还原酶内的质子耦合电子转移

细胞色素 P450 酶在生物合成和代谢转化中发挥着关键作用。特别是，细胞色素 P450 还原酶 (CPR) 充当 P450 单加氧酶氧活化的关键电子供体，但 CPR 内的电子转移机制在很大程度上是难以捉摸的。在这里，进行了大量的分子动力学 (MD) 和量子力学/分子力学 (QM/MM) 计算，以阐明 CPR 的电子转移机制。我们发现从 FADH 到 FMN 的电子转移^是通过质子耦合电子转移（PCET）机制发生的。在这里，Glu142 通过两个水分子链将质子转移到 FMN，同时电子从 FADH 转移^到FMN。随后从 FADH• 到 FMNH• 的 ET 涉及 Asp675 介导的 PCET 过程，其中 Ser457 辅助的质子从 FADH• 到 Asp675 的转移与从 FADH• 到 FMNH• 的电子转移相结合。值得注意的是，双质子化 His180 产生的局部电场在动力学和热力学上显着增强了 PCET 反应。这项研究强调了局部电场在促进酶反应的生物电子转移中的重要作用。