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，详细的血红素酶降解模型。在 在生物系统中，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，例如 如：胆绿素、葡萄球菌素和菌胆素。在真核生物中，释放的非血红素铁最终被回收到 铁依赖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， 病原生物体从宿主来源的血红素获得铁。尽管对总体情况有一个普遍的了解， 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， 两到三个氧原子的血红素底物仍然知之甚少。这种机械知识是 需要选择性地靶向血红素加氧酶而不破坏其他血红素依赖性蛋白。最近我们 开发了新的光学分析，以准确测量血红素结合常数，并阐明 血红素加氧酶和其他血红素依赖性蛋白质之间的血红素。我们还发现了一个 在一些血红素加氧酶活性位点内血红素的前所未有的动态平面外变形， 与酶活性相关。最后，我们揭示了活性位点氢键促进血红素 通过用阳离子稳定共振结构降解产生葡萄球菌蛋白的血红素加氧酶 氧合的碳位点上的自由基。在接下来的五年里，我们将采用一种结合光谱和 计算方法来阐明血红素单氧化为meso-羟基血红素的机制， 产生菌胆素的血红素加氧酶，以及胆绿素- 和产生葡萄球菌白蛋白的血红素加氧酶。一般来说，我们将采用各种光谱技术， 技术来表征关键酶中间体的类似物。这些实验数据将用于 开发酶促反应的精确计算模型。最终，该计划将提供 详细了解血红素生物化学的一个迷人的章节，即自我氧化。

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.