Heme Oxygenases: chemically complex enzymes found in diverse biological pathways

项目摘要 这项研究计划将开发准确、详细的酶促血红素降解模型。在……里面 生物系统，血红素加氧酶将血红素降解为非血红素铁和含氧有机产物，如 AS：胆绿素、葡萄球菌素和霉菌胆碱。在真核生物中，释放出来的非血红素铁最终被循环利用成 依赖铁的蛋白质。在原核生物中，血红素加氧酶通常是铁获取途径的一部分，从而 病原体从宿主来源的血红素中获取铁。尽管总体上对 由血红素加氧酶催化的反应，这些酶如何催化插入的机制细节 两到三个氧原子进入血红素底物的情况仍然知之甚少。这种机械论的知识是 需要选择性地靶向血红素加氧酶，而不破坏其他依赖于血红素的蛋白质。最近，我们 开发了新的光学分析方法来准确测量血红素结合常数和阐明血红素的分配 血红素加氧酶和其他依赖于血红素的蛋白质之间的血红素。我们还发现了一个 一些血红素加氧酶活性部位中的血红素前所未有的、动态的平面外扭曲，这是 与酶活性相关。最后，我们揭示了活性中心氢键促进了亚铁血红素 阳离子稳定共振结构对金黄色葡萄球素产生的血红素加氧酶的降解作用 在氧化的碳位上的自由基。在接下来的五年里，我们将使用联合光谱和 用计算方法阐明血红素单氧化为中羟基血红素的机理 产生霉菌胆红素的血红素加氧酶，以及胆绿素氧化中羟基血红素的机制. 以及产生葡萄球素的血红素加氧酶。总体而言，我们将采用多种光谱技术 表征关键酶中间体类似物的技术。这些实验数据将被用来 开发酶反应的精确计算模型。最终，该计划将提供 详细洞察了血红素生物化学的一个引人入胜的章节，即自氧合作用。

Project Summary This research program will develop accurate, detailed models of enzymatic heme degradation. In biological systems, heme oxygenases degrade heme to non-heme iron and oxygenated organic products, such as: biliverdin, staphylobilin, and mycobilin. In eukaryotes, the liberated non-heme iron is ultimately recycled into iron-dependent proteins. In prokaryotes, heme oxygenases are often part of iron acquisition pathways whereby pathogenic organisms acquire iron from host-derived heme. Despite a general understanding of the overall reactions catalyzed by heme oxygenases, the mechanistic details of how these enzymes catalyze the insertion of two to three oxygen atoms into a heme substrate remain poorly understood. This mechanistic knowledge is needed to selectively target heme oxygenase without disrupting other heme-dependent proteins. Recently, we developed new optical assays to accurately measure heme binding constants and elucidate the partitioning of heme between heme oxygenases and other heme-dependent proteins. We have also discovered an unprecedented, dynamic out-of-plane distortion of heme within some heme oxygenase active sites, which is correlated with enzymatic activity. Finally, we have revealed that an active site hydrogen bond promotes heme degradation in staphylobilin-producing heme oxygenases by stabilizing a resonance structure with a cationic radical at the carbon site of oxygenation. In the next five years, we will employ a combined spectroscopic and computational approach to elucidate the mechanism of heme monooxygenation to meso-hydroxyheme by mycobilin-producing heme oxygenases, and the mechanisms of meso-hydroxyheme oxygenation by biliverdin- and staphylobilin-producing heme oxygenases. In general, we will employ a variety of spectroscopic techniques to characterize analogues of key enzymatic intermediates. These experimental data will be used to develop accurate computational models of the enzymatic reactions. Ultimately, this program will provide detailed insight into a fascinating chapter of heme biochemistry, namely, self-oxygenation.