Cowley Ryan E, Tian Li, Solomon Edward I
Department of Chemistry, Stanford University, Stanford, CA 94305.
Department of Chemistry, Stanford University, Stanford, CA 94305; Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Stanford University, Menlo Park, CA 94025
Proc Natl Acad Sci U S A. 2016 Oct 25;113(43):12035-12040. doi: 10.1073/pnas.1614807113. Epub 2016 Oct 10.
Peptidylglycine α-hydroxylating monooxygenase (PHM) and dopamine β-monooxygenase (DβM) are copper-dependent enzymes that are vital for neurotransmitter regulation and hormone biosynthesis. These enzymes feature a unique active site consisting of two spatially separated (by 11 Å in PHM) and magnetically noncoupled copper centers that enables 1e activation of O for hydrogen atom abstraction (HAA) of substrate C-H bonds and subsequent hydroxylation. Although the structures of the resting enzymes are known, details of the hydroxylation mechanism and timing of long-range electron transfer (ET) are not clear. This study presents density-functional calculations of the full reaction coordinate, which demonstrate: (i) the importance of the end-on coordination of superoxide to Cu for HAA along the triplet spin surface; (ii) substrate radical rebound to a Cu hydroperoxide favors the proximal, nonprotonated oxygen; and (iii) long-range ET can only occur at a late step with a large driving force, which serves to inhibit deleterious Fenton chemistry. The large inner-sphere reorganization energy at the ET site is used as a control mechanism to arrest premature ET and dictate the correct timing of ET.
肽基甘氨酸α-羟化单加氧酶（PHM）和多巴胺β-单加氧酶（DβM）是铜依赖性酶，对神经递质调节和激素生物合成至关重要。这些酶具有独特的活性位点，由两个在空间上分离（在PHM中相距11 Å）且磁非耦合的铜中心组成，该活性位点能够使O发生单电子活化，以提取底物C-H键的氢原子（HAA）并随后进行羟基化。尽管已知静息酶的结构，但羟基化机制和长程电子转移（ET）的时间细节尚不清楚。本研究给出了全反应坐标的密度泛函计算结果，这些结果表明：（i）超氧化物以端基配位方式与Cu结合对于沿三重态自旋表面进行HAA的重要性；（ii）底物自由基反弹至铜氢过氧化物有利于近端的非质子化氧；（iii）长程ET仅在后期以较大驱动力发生，这有助于抑制有害的芬顿化学。ET位点处较大的内球重组能被用作一种控制机制，以阻止过早的ET并确定ET的正确时间。
