Understanding the Selectivity of Oxygen Activation by Model Iron-Porphyrin Catalysts

了解铁卟啉模型催化剂对氧活化的选择性

• 批准号: 9758473
• 负责人: Anna Brezny
• 金额: $ 6.12万
• 依托单位: YALE UNIVERSITY
• 依托单位国家: 美国
• 财政年份: 2019
• 资助国家: 美国
• 起止时间: 2019-05-01 至 2022-04-30
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/9758473
• 关键词: Acidity; Acids; Active Sites; Affect; Binding; Biological Models; Catalysis; Chemistry; Complex; Consumption; Coupled; Cytochrome P450; Cytochrome c Peroxidase; Data; Dependence; Dioxygen; Disease; Distal; Enzymes; Generations; Goals; Heme; Human body; Hydrogen Bonding; Hydrogen Peroxide; Individual; Iron; Kinetics; Laws; Lead; Ligands; Light; Literature; Measurable; Measures; Metalloproteins; Modeling; Mutagenesis; Nature; Oxidases; Oxidative Stress; Oxides; Oxygen; Oxygenases; Pathway interactions; Play; Porphyrins; Process; Production; Prostaglandin-Endoperoxide Synthase; Proteins; Protons; Reaction; Reactive Oxygen Species; Reducing Agents; Role; Site; Structure; System; Testing; Water; Work; adduct; analog; catalyst; cold temperature; cytochrome c oxidase; experimental study; insight; metalloenzyme; preference; prevent; protonation; stoichiometry

PROJECT SUMMARY Heme-containing proteins are among the most abundant metalloproteins in nature. A significant subset of these catalysts perform reactions utilizing dioxygen (O2), including cytochrome c oxidase (CcO) which reduces dioxygen to water, and cytochrome P450 (CYP) which activates dioxygen in order to oxidize organic substrates. The functions of CYP and CcO rely on their abilities to reduce O2 to water. In an “uncoupled” process, some equivalents of reductant are wasted and reactive oxygen species (ROS) such as H2O2 are released. ROS are known to lead to oxidative stress and a variety of diseases in the human body, so developing an understanding of this uncoupling is important. It is hypothesized that a catalytic Fe–OOH intermediate is the site of bifurcation between H2O and H2O2 formation. This hydroperoxy intermediate is ubiquitous in heme-containing enzymes including cytochrome c peroxidase, heme oxygenase, and prostaglandin H synthase. In all cases, proper proton delivery is necessary for O–O bond cleavage. Mutagenesis studies of P450cam have made it clear that the role of protons and H-bonding are important in understanding selectivity, but there is debate as to how the conserved residues prevent uncoupling. Additionally, the canonical mechanism involves one proton addition to either the proximal or distal oxygen atom of the Fe–OOH intermediate to yield H2O2 or H2O, respectively, but there is no direct evidence of this stoichiometry. Our preliminary data suggests that the desired distal protonation may involve a higher dependence on protons. Therefore our goal is to study what governs the selectivity between formation of H2O or release of H2O2 from this critical Fe–OOH intermediate. Our work in this proposal seeks to understand the selectivity of H2O and H2O2 formation from heme enzymes utilizing a simple model system. Synthetic analogues provide the advantage of allowing us to systematically vary and control structural entities, enter the catalytic cycle in new places, and independently synthesize intermediates. Therefore, we propose to study the selectivity of O2 activation by Fe-porphyrin catalysts proceeding through the same Fe–OOH intermediate. First, we will explore how various reaction conditions (concentration, pKa, and structure of the acid) affect selectivity in the catalytic oxygen reduction reaction (ORR). Secondly, we will study a variety of catalysts with varied H-bonding motifs to better understand how the residues in an active site may influence selectivity. Additionally, we will explore the non-catalytic reactivity of the Fe–OOH intermediate to gain independent measures of the relative rates of H2O and H2O2 formation under varied conditions. Ultimately, our goal is to understand how the reaction conditions and H- bonding networks affect H2O versus H2O2 selectivity in a model system. This understanding will provide insight into how enzymes can control the reactivity of the critical Fe-hydroperoxy intermediate to minimize ROS formation in a variety of heme-containing active sites.

项目概要 含血红素的蛋白质是自然界中最丰富的金属蛋白质的一个重要子集。 这些催化剂减少利用双氧 (O2) 的反应，包括细胞色素 c 氧化酶 (CcO)， 分子氧转化为水，细胞色素 P450 (CYP) 激活分子氧以氧化有机物 CYP 和 CcO 的功能依赖于它们以“非耦合”方式将 O2 还原为水的能力。 过程中，一些当量的还原剂被浪费，活性氧 (ROS) 如 H2O2 被浪费。 已知ROS的释放会导致人体氧化应激和多种疾病。 加深对这种解偶联的理解非常重要。 中间体是 H2O 和 H2O2 形成之间的分叉位点，该氢过氧中间体是。 普遍存在于含血红素的酶中，包括细胞色素 C 过氧化物酶、血红素加氧酶和 在所有情况下，适当的质子传递对于 O-O 键裂解都是必要的。 P450cam 的诱变研究清楚地表明质子和氢键的作用很重要 在理解选择性方面，但对于保守残基如何防止解偶联存在争议。 此外，规范机制涉及向近端或远端氧原子添加一个质子 Fe-OOH中间体分别产生H2O2或H2O，但没有直接证据表明这一点 我们的初步数据表明，所需的远端质子化可能涉及更高的值。 因此，我们的目标是研究控制 H2O 形成之间选择性的因素。 或从这种关键的 Fe-OOH 中间体中释放 H2O2。 我们在本提案中的工作旨在了解血红素形成 H2O 和 H2O2 的选择性 利用简单的模型系统的酶提供的优势使我们能够 系统地改变和控制结构实体，在新的地方进入催化循环，并独立地 因此，我们建议研究Fe-卟啉对O2活化的选择性。 催化剂通过相同的 Fe-OOH 中间体进行首先，我们将探讨各种反应是如何进行的。 条件（酸的浓度、pKa 和结构）影响催化氧还原的选择性 反应（ORR）。其次，我们将研究具有不同氢键基序的各种催化剂，以更好地理解 此外，活性位点中的残基如何影响选择性。 Fe-OOH 中间体的反应性，以获得 H2O 和 H2O2 相对速​​率的独立测量 最终，我们的目标是了解反应条件和 H- 的形成方式。 键合网络影响模型系统中 H2O 与 H2O2 的选择性。 研究酶如何控制关键的铁-氢过氧中间体的反应性，以最大限度地减少活性氧 多种含血红素活性位点的形成。