Department of Chemistry, Stanford University, Stanford, California 94305, United States.
Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Stanford University, Menlo Park, California 94025, United States.
J Am Chem Soc. 2023 Jul 26;145(29):16015-16025. doi: 10.1021/jacs.3c04048. Epub 2023 Jul 13.
Lytic polysaccharide monooxygenases (LPMOs) catalyze the degradation of recalcitrant carbohydrate polysaccharide substrates. These enzymes are characterized by a mononuclear Cu(I) active site with a three-coordinate T-shaped "His-brace" configuration including the N-terminal histidine and its amine group as ligands. This study explicitly investigates the electronic structure of the d Cu(I) active site in a LPMO using Kβ X-ray emission spectroscopy (XES). The lack of inversion symmetry in the His-brace site enables the 3d/p mixing required for intensity in the Kβ valence-to-core (VtC) XES spectrum of Cu(I)-LPMO. These Kβ XES data are correlated to density functional theory (DFT) calculations to define the bonding, and in particular, the frontier molecular orbital (FMO) of the Cu(I) site. These experimentally validated DFT calculations are used to evaluate the reaction coordinate for homolytic cleavage of the HO O-O bond and understand the contribution of this FMO to the low barrier of this reaction and how the geometric and electronic structure of the Cu(I)-LPMO site is activated for rapid reactivity with HO.
溶细胞多糖单加氧酶（LPMOs）催化难降解碳水化合物多糖底物的降解。这些酶的特征是单核 Cu（I）活性位点，具有三配位 T 形“His-brace”构型，包括 N 端组氨酸及其胺基作为配体。本研究使用 Kβ X 射线发射光谱（XES）明确研究了 LPMO 中 d Cu（I）活性位点的电子结构。His-brace 位点的非反演对称允许 3d/p 混合，这是 Cu（I）-LPMO 的 Kβ 价到核（VtC）XES 光谱中强度所必需的。这些 Kβ XES 数据与密度泛函理论（DFT）计算相关联，以定义键合，特别是 Cu（I）位点的前沿分子轨道（FMO）。这些经过实验验证的 DFT 计算用于评估 HO O-O 键的均裂裂解的反应坐标，理解该 FMO 对该反应低能垒的贡献，以及 Cu（I）-LPMO 位点的几何和电子结构如何被激活以实现与 HO 的快速反应性。
