The Biological Role of Heme in Human Nutrition

描述：血红素（铁原卟啉IX）是在许多生物过程中起关键作用的蛋白质修复基团，包括氧化代谢、双原子气体的合成和传感、细胞分化、外源解毒、转录水平的基因调控、蛋白质翻译和靶向以及蛋白质稳定性。人类利用红肉中的血红素作为铁的来源，因为血红素在肠道中比无机铁更容易吸收。在真核生物中，血红素在线粒体内合成。游离血红素不溶于水环境，由于过氧化物酶的活性而具有细胞毒性。因此，一个初步的论点可以提出，在细胞内，血红素从合成位点转运到细胞内不同的目的地，将血红素掺入载脂蛋白。血红素是通过一个多步骤的生物合成途径合成的，具有明确的中间体，被认为在整个进化过程中高度保守。这些研究的长期目标是确定哺乳动物系统中营养血红素稳态的分子和细胞决定因素。拟进行的研究将利用秀丽隐杆线虫作为遗传模式生物来阐明血红素摄取、封存、运输和纳入血红蛋白的途径。我们将利用荧光血红素类似物、脉冲追踪分析和[59Fe]血红素代谢标记的血红素摄取和结合试验，在显微镜下评估秀丽隐杆线虫血红素获取的生化机制。通过筛选和分类在正常生长和发育中具有血红素依赖性缺陷的突变体，将确定秀丽隐杆线虫血红素运输的分子和细胞途径。突变体将被生物化学表征，突变将通过基因重组和SNP作图进行定位。这些研究结果将为真核生物血红素稳态提供新的机制见解，并可能有助于开发以血红素为基础的人类铁缺乏营养干预措施，并允许设计新的药物靶点来调节外源代谢。

DESCRIPTION: Heme (iron-protoporphyrin IX) is the prosthetic group of proteins which play a key role in many biological processes including oxidative metabolism, the synthesis and sensing of diatomic gases, cellular differentiation, xenobiotic detoxification, gene regulation at the level of transcription, protein translation and targeting, and protein stability. Humans utilize heme as a source of iron from red meat because heme is more readily absorbed than inorganic iron in the intestine. In eukaryotes, heme is synthesized within the mitochondria. Free heme is insoluble in aqueous milieu and is cytotoxic due to peroxidase activity. Thus, a prima facie argument can be made that within cells specific pathways exist for the trafficking of heme from site of synthesis to various intracellular destinations for the incorporation of heme into apo-hemoproteins. Heme is synthesized via a multistep biosynthetic pathway with well-defined intermediates that were thought to be highly conserved through out evolution. The long-term objective of these studies is to define the molecular and cellular determinants of nutritional heme homeostasis in mammalian systems. The proposed studies will utilize C. elegans as a genetic model organism to elucidate pathways for heme uptake, sequestration, trafficking, and incorporation into hemoproteins. The biochemical mechanisms for heme acquisition in C. elegans will be evaluated by microscopy using fluorescent heme analogs, pulse-chase analysis, and heme uptake and incorporation assays using metabolic labeling with [59Fe]heme. The molecular and cellular pathways for heme trafficking in C. elegans will be identified by screening and classifying mutants that have heme-dependent defects in normal growth and development. The mutants will be charaterized biochemically, and the mutations will be mapped and localized by genetic recombination and SNP mapping. The results from these studies will provide new mechanistic insights into heme homeostasis in eukaryotes and may aid in the development of heme-based nutritional interventions for human iron deficiency, and permit design of novel drug targets to modulate xenobiotic metabolism.