Electronic Structure of Heme Enzyme Intermediates from Resonant Inelastic X-ray Scattering and L-Edge X-ray Absorption Spectroscopy

共振非弹性 X 射线散射和 L 边 X 射线吸收光谱研究血红素酶中间体的电子结构

• 批准号: 9768514
• 负责人: LELAND BRUCE GEE
• 金额: $ 6.37万
• 依托单位: STANFORD UNIVERSITY
• 依托单位国家: 美国
• 财政年份: 2017
• 资助国家: 美国
• 起止时间: 2017-09-16 至 2021-09-15
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/9768514
• 关键词: 3-Dimensional; Academia; Affect; Apoptosis; Biological; Biology; Cations; Characteristics; Chemistry; Complex; Coupled; Cysteine; Cytochrome P450; Data Analyses; Detection; Development; Dioxygen; Drug Metabolic Detoxication; Due Process; Electron Transport; Electrons; Electrostatics; Environment; Enzyme Reactivation; Enzymes; Exhibits; Fluorescence; Genes; Health; Heme; Heme Iron; Histidine; Hormones; Human; Human Genome; Hydrogen Bonding; Hydroxylation; Iron; Knowledge; Ligands; Ligation; Mechanics; Mentorship; Methionine; Methods; Modeling; Nature; Noise; Optics; Outcome; Oxygen; Photons; Play; Porphyrins; Property; Pterins; Reaction; Research; Resolution; Roentgen Rays; Role; Sampling; Site; Spectrum Analysis; Steroid biosynthesis; Structure; System; Techniques; Tyrosine; Vacuum; Work; X ray spectroscopy; absorption; alpha ketoglutarate; base; biological systems; career; cholesterol biosynthesis; circular magnetic dichroism; cofactor; computational chemistry; cytochrome c; detector; driving force; drug metabolism; electronic structure; frontier; heme a; innovation; insight; interest; molecular orbital; oxygen transport; porphyrin a; preference; quantum; sensor; simulation; steroid hormone; steroid metabolism; tool

Project Summary/Abstract Much work has been performed to study reactive electron orbitals in nonheme enzymes (NHE) and their activation of oxygen. Similar to NHEs, heme-containing enzymes play a diverse set of roles in the biosphere and factor heavily to human health: detoxification, oxygen transport, and hormone synthesis. It is important that heme enzymes be understood to a similar extent as NHEs, however the tools used to characterize NHE electron covalency of Fe, such as magnetic circular dichroism optical spectroscopy, are not as applicable to hemes due to the highly delocalized equatorial porphyrin ring that obscures the covalency of the Fe atom. The covalency of the low-lying valence orbitals of the heme site, actively tunes intermediates for their function in biology. To directly probe the Fe center in heme enzymes, this project will use the relatively new resonant inelastic X-ray scattering (RIXS) spectroscopy. 1s2p RIXS uses K-edge, hard X-ray, incident photons and detects the subsequent 2p to 1s hole-filling resulting in the same final state as L-edge X-ray absorption spectroscopy (XAS) – with different selection rules. RIXS yields information about the electronic structure of the frontier molecular orbitals (FMOs), specifically d orbital covalency, critical to studying oxygen activation by hemes, however without the weaknesses inherent in soft X-ray L-edge XAS such as high vacuum requirements, high sample concentrations, and fluorescence inhibition. However, a new ultra-low noise detector called the TES will finally allow Fe L-edge XAS spectra of dilute enzyme samples, and correlating 1s2p RIXS with L-edge XAS will afford the differential orbital covalency of the frontier molecular orbitals that are key to reactivity. Initially, the trainee will apply RIXS and L- edge XAS to nonheme and heme model complexes, particularly the well-understood nonheme models will allow development of the experimentally observed 4p orbital mixing into the simulation of RIXS spectra. The trainee will then explore the change of the Fe=O bond when going from a nonheme to a heme environment in an enzyme. With L-edge XAS and RIXS the reactive orbitals of cytochrome p450 compound II will reveal the driving forces for the “rebound mechanism” of hydroxylation. Next, this study will explore the change in the Fe=O bond upon conversion to the compound I radical cation intermediate and the implications for H-atom abstraction. Finally, the frontier molecular orbitals of compound I will be compared across the different trans axial ligations in heme enzymes. This interchange of the axial ligand (histidine, cysteine, and tyrosine) will quantitively identify the, currently, loosely defined “push” and “pull” effects on the heme electronic structure that allow heterolytic O2 cleavage. This project will further the fundamental knowledge of Fe oxygen chemistry in heme, and nonheme, enzymes. Providing new insights into the nature and reactivity of the Fe=O bond, the role that the porphyrin plays in hemes, and how that is adapted in NHEs where no such electron sink is available. This work will also develop the methods and modelling of 1s2p RIXS and TES detected L-edge XAS on bioinorganic systems.

项目摘要/摘要 已经进行了许多工作，以研究非血红素酶（NHE）的反应性电子轨道及其 氧气的激活。与nhes相似，含血红素的酶在生物圈中起着多种作用 对人类健康的严重因素：解毒，氧运输和骑马的合成。血红素很重要 将酶理解的程度与NHE相似，但是用于表征NHE电子的工具 FE的共价（例如磁圆二分色光谱法）不适用于HEMES。 到高度离域的赤道卟啉环，掩盖了Fe原子的共价。的共价 血红素位点的低凹价轨道积极调节中间体在生物学中的功能。直接 探测血红素酶的FE中心，该项目将使用相对较新的弹性非弹性X射线散射 （RIX）光谱法。 1S2P rixs使用K-边缘，硬X射线，事件照片并检测到后续2p 1S填充填充，导致与L边缘X射线抽象光谱（XAS）相同的最终状态 - 选择规则。 RIX产生有关边界分子轨道（FMOS）的电子结构的信息 特别是d轨道的共价，对于研究血液的氧气激活至关重要，但是没有弱点 软X射线L边缘XAS固有的，例如高真空需求，高样品浓度和 荧光抑制。但是，一个称为TE的新的超低噪声检测器最终将允许fe l-gedge xas 稀酶样品的光谱，并将1S2P RIX与L边缘XAS相关 边界分子轨道的共价是反应性的关键。最初，学员将应用RIX和L- 边缘XAS到非血红素和血红素模型复合物，尤其是理解的非血红素模型将允许 实验观察到的4p轨道混合到Rixs光谱的模拟中的开发。实习生 然后，将从酶中的非血红素到血红素环境时探索Fe = O键的变化。 使用L边缘XAS和RIXS，细胞色素P450化合物II的反应性轨道将揭示驱动力 用于羟基化的“反弹机制”。接下来，这项研究将探索Fe = O Bond的变化 转化为化合物I自由基阳离子中间体以及对H原子抽象的影响。最后， 化合物I的前沿分子轨道将在血红素中的不同跨轴线上进行比较 酶。轴向配体的这种互换（组氨酸，半胱氨酸和酪氨酸）将定量识别， 当前，对允许杂化O2的血红素电子结构的“推动”和“拉动”效果松散定义 乳沟。该项目将进一步进一步了解Heme中Fe氧化学的基本知识，而Non -eme， 酶。提供有关Fe = O键的性质和反应性的新见解，卟啉的作用 在没有这种电子水槽的NHES中，在Hemes中发挥作用。这项工作也将 在生物无机系统上开发了1S2P RIX和TES检测到的L边缘XAS的方法和建模。