Comparative Heme Metabolism in Divergent Eukaryotes

项目总结/摘要 血红素是一种古老的生物辅因子，在线粒体氧化还原化学、能量代谢和代谢中起着关键作用。 从人类到微生物病原体的所有真核细胞中的生产和信号传导。尽管功能 不同的真核生物在依赖血红素方面有相似之处，它们进化出了不同的分子适应， 血红素代谢以满足特定的细胞需求。线粒体血红素关键特征的比较和对比 因此，代谢可以揭示血红素运输和利用的一般原则，以及揭示独特的 适应性突出了真核生物之间的进化多样性。阐明这些一般原则将 增加对血红素相关线粒体功能障碍的了解，这些功能障碍是人类重大疾病的基础。 了解血红素代谢的功能差异，可以开发新的病原体特异性 避免人类毒性的治疗方法。在这份提案中，我们列出了我们研究计划的长期目标 深入了解线粒体血红素代谢的关键生化特性和机制 也是人类的主要病原体在未来五年，我们将致力于实现这一目标。 细胞色素c的生物发生和功能的分子机制的研究，是一个重要的， 一种易于处理的血红素结合蛋白，具有主要的未解决的机制特征， 线粒体血红素代谢及其在真核生物中的保守性和多样性。细胞色素c具有 线粒体电子传递链（ETC）中保守的基本功能， 作为信号细胞凋亡开始的过氧化物酶的单独作用。细胞色素c的分子特征， 支撑其从ETC到过氧化物酶活性的功能性转变仍然很少定义。细胞色素c 与其他血红素结合蛋白的区别在于其使用保守的CXXCH序列基序共价连接 通过稳定的硫醚键结合血红素。这种共价连接需要线粒体膜间隙 (IMS)全细胞色素c合成酶（HCCS）。虽然HCCS功能是所有真核生物的基础， 呼吸，HCCS的结构是未知的，因此对其附着血红素的机制有分子见解。 细胞色素C缺乏。此外，仍不清楚血红素如何从其代谢产物被运输到IMS中的HCCS。 线粒体基质内的合成位点。我们建议对人类细胞和 疟原虫寄生虫侵入富含血红素的人类红细胞，以应对以下关键挑战：1） 确定细胞色素c介导ETC和过氧化物酶活性之间转换的分子特征; 2)阐明HCCS的三维结构，阐明其血红素化的分子机制 3）确定HCCS获取血红素的机制。这项工作将 推进对人类线粒体血红素代谢的基本理解， 病原体，并为血红素代谢的长期综合研究提供平台， 从我们最初关注细胞色素c中吸取的教训。

PROJECT SUMMARY/ABSTRACT Heme is an ancient biological cofactor that plays critical roles in mitochondrial redox chemistry, energy production, and signaling in all eukaryotic cells from humans to microbial pathogens. Despite functional similarities in their reliance on heme, divergent eukaryotes have evolved distinct molecular adaptations that tune heme metabolism to particular cellular demands. Comparing and contrasting key features of mitochondrial heme metabolism can thus reveal general principles in heme trafficking and utilization, as well as unveil unique adaptations that highlight the evolutionary diversity among eukaryotes. Elucidating these general principles will increase understanding of heme-related mitochondrial dysfunctions that underpin major human diseases. Understanding of functional differences in heme metabolism can be exploited to develop new pathogen-specific therapies that avoid human toxicity. In this proposal, we lay out a long-term goal of our research program to deeply understand key biochemical properties and mechanisms of mitochondrial heme metabolism in humans and a major human pathogen. In pursuing this goal over the next five years, we will focus our studies on understanding the molecular mechanisms of biogenesis and function of cytochrome c, a critical and tractable heme-binding protein with major unresolved mechanistic features that exemplifies key features of mitochondrial heme metabolism and its conservation as well as diversity between eukaryotes. Cytochrome c has a conserved essential function in the mitochondrial electron transport chain (ETC) but also plays an important, separate role as a peroxidase that signals the onset of apoptosis. The molecular features of cytochrome c that underpin its functional transition from ETC to peroxidase activity remain sparsely defined. Cytochrome c is distinguished from other heme-binding proteins by its use of a conserved CXXCH sequence motif to covalently bind heme via stable thioether bonds. This covalent attachment requires the mitochondrial intermembrane space (IMS) enzyme, holo cytochrome c synthase (HCCS). Although HCCS function is fundamental to all eukaryotic respiration, the structure of HCCS is unknown and thus molecular insight into its mechanism of attaching heme to cytochrome c is lacking. Furthermore, it remains unknown how heme is trafficked to HCCS in the IMS from its site of synthesis within the mitochondrial matrix. We propose comparative studies between human cells and Plasmodium parasites that invade heme-rich human erythrocytes to tackle the following key challenges: 1) to define the molecular features of cytochrome c that mediate its transition between ETC and peroxidase activities; 2) to elucidate the three-dimensional structure of HCCS and unravel its molecular mechanism of heme attachment to cytochrome c; and 3) to determine the mechanism of heme acquisition by HCCS. This work will advance fundamental understanding of mitochondrial heme metabolism in humans and a critical human pathogen and provide a platform for longer-term integrative studies of heme metabolism that will test and extend the lessons learned from our initial focus on cytochrome c.