PURE UNDER CARBON DIOXIDE

这个子项目是许多研究子项目中利用 资源由NIH/NCRR资助的中心拨款提供。子项目和 调查员(PI)可能从NIH的另一个来源获得了主要资金， 并因此可以在其他清晰的条目中表示。列出的机构是 该中心不一定是调查人员的机构。 对大肠杆菌和五倍子羧氨基咪唑核糖核苷酸合成酶(PURES)的生化研究和基因组分析表明，这些嘌呤生物合成酶在高度保守的初级代谢途径中提供了一个不寻常的进化分歧的例子。I类蛋白以大肠杆菌蛋白为代表，在大多数原核生物和真菌中发现，催化CO(2)基团从N5-羧氨基咪唑核苷酸(N5-CAIR)的氨基甲酸酯可逆转移到C4，生成4-羧氨基咪唑核苷酸(CAIR)。另一方面，在高等真核生物中发现的以胆囊虫酶为代表的II类蛋白，通过将CO(2)可逆转移到氨基咪唑核苷酸(AIR)而形成CAIR。目前的结构研究涉及I类纯(N5-羧氨基咪唑变位酶)，重点是其化学上独特的变位酶反应。一种工作机制假说涉及组氨酸(在大肠杆菌中纯His45)作为一种普通酸发挥作用，但没有获得多个质子化状态的证据。结构研究对于更好地理解其机理将是非常重要的。我们正在特别研究His45突变体的结构。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Biochemical studies and genomic analyses of the Escherichia coli and Gallus gallus carboxyaminoimidazole ribonucleotide synthases (PurEs) indicate that these purine biosynthetic enzymes provide an unusual example of evolutionary divergence in a highly conserved, primary metabolic pathway. Class I PurEs, typified by the E. coli protein and found in most prokaryotes and fungi, catalyze the reversible transfer of a CO(2) group from the carbamate of N5-carboxyamino imidazole ribonucleotide (N5-CAIR) to C4, yielding 4-carboxy aminoimidazole ribonucleotide (CAIR). On the other hand, class II PurEs, typified by the G. gallus enzyme and found in higher eukaryotes, form CAIR by reversible transfer of CO(2) to aminoimidazole ribonucleotide (AIR). The current structural study involves class I PurE (N5-carboxyaminoimidazole mutase) with an emphasis on its chemically unique mutase reaction. A working mechanistic hypothesis involves a histidine (His45 in E. coli PurE) functioning as a general acid, but no evidence for multiple protonation states has been obtained. The structural study will be very important for getting a better understanding of the mechanism. We are in particular studying the structures of the mutants of His45.