Structure and function of enzymes involved in the biosynthesis and transport of heme

血红素是能量守恒、电子传递复合物和各种酶和蛋白质的重要辅因子。我们正在系统地研究复杂的血红素生物合成途径中的酶和卟啉转运蛋白的结构-功能关系。最近，我们已经确定了第一个晶体结构的天然误充电谷氨酰-tRNA合成酶，5-氨基乙酰丙酸合成酶（HemA）和“自由基SAM酶”粪卟啉原III氧化酶（HemN）。使用生物物理方法成功地研究了这些和另外两种酶（HemB，HemY）的催化机制。沿着这些思路，我们接下来将研究一种新型非氧依赖性原卟啉原IX氧化酶（HemG）的结构与功能关系。其独特的FMN为基础的催化，其中包括一个6电子转移到膜本地化的电子传递链将被研究。我们解决的HemA的结构作为基础，逐步阐明其催化机制，使用突变酶和底物类似物的组合。将研究各种血红素生物合成酶之间的体内和体外蛋白质-蛋白质和蛋白质-代谢物相互作用及其对代谢通道的功能后果。最后，四吡咯通过线粒体膜运输的分子基础将使用结构功能的方法进行研究。长期目标是在原子水平上详细了解生物化学和生命中一个中心生物合成途径的调节。

Hemes are essential cofactors for energy-conserving, electron transport complexes and various enzymes and proteins. We are systematically investigating the structure-function relationship of enzymes and porphyrin transporters involved in the complex heme biosynthetic pathway. Recently, we have determined the first crystal structures of a natural mischarging glutamyl-tRNA synthetase, 5-aminolevulinic acid synthase (HemA) and the “Radical SAM enzyme” coproporphyrinogen III oxidase (HemN). The catalytic mechanisms of these and two further enzymes (HemB, HemY) were successfully investigated using biophysical methods. Along these lines we will next investigate the structure-function relationship of a novel oxygen independent protoporphyrinogen IX oxidase (HemG). Its unique FMN-based catalysis which includes a 6-electron transfer to membrane-localized electron transport chains will be studied. Our solved structure of HemA serves as basis for the stepwise elucidation of its catalytic mechanism using a combination of mutant enzymes and substrate analogs. In vivo and in vitro protein-protein and protein-metabolite interactions between various heme biosynthetic enzymes and their functional consequences for metabolic channeling will be studied. Finally, the molecular basis of tetrapyrrole transport via mitochondrial membranes will be studied using a structurefunction approach. The long term goal is the detailed understanding of the biochemistry and regulation of one of the central biosynthetic pathways in life at the atomic level.