STRUCTURAL STUDIES OF GLUTAMINE AMIDOTRANSFERASES

氮与生物分子的结合是通过 一种叫做谷氨酰胺转移酶的酶家族的作用。 这些酶将NH3从谷氨酰胺的侧链转移到 合适的基质。 至少有十四种不同的谷氨酰胺 酰胺基转移酶，每一种催化NH3转移到不同的 衬底 序列指纹已被确定，分配所有 已知的谷氨酰胺转移酶序列属于两个家族之一。 无论是NH3的产生机制，还是NH3与NH3之间的紧密耦合， NH3的产生和NH3的运输对于任何酶都是已知的。 生物催化中的这一重要问题正由 确定三种不同的三维结构 谷氨酰胺酰胺转移酶在两个家庭的X射线晶体学。 其中两个结构测定是通过多波长 异常衍射和代表重要的新的应用，这 晶体学方法 1.谷氨酰胺PRPP酰胺转移酶催化第一个关键步骤 嘌呤核苷酸的从头合成。 嘌呤缺陷 途径与疾病如高尿酸血症（痛风）有关， 免疫缺陷和神经系统症状。 晶体结构正在被 测定来自两个B的酶。subtilis和E.大肠杆菌， 阐明B中一个不寻常的金属中心的功能。二联活 高等真核生物，显然具有新的调节功能， 不是催化剂。 2. GNP合成酶，另一种来自嘌呤途径的酶，是一种靶点。 试图阻止细胞生长，特别是肿瘤细胞生长和T细胞 增殖 底物和ATP结合的GMP合成酶晶体 单独的酶晶体是一个很好的结构系统， NH_3生成和NH_3转移活动的耦合研究。 3.咪唑甘油3-磷酸合酶，一种来自组氨酸的酶 途径，是异二聚谷氨酰胺转移酶。

The incorporation of nitrogen into biological molecules occurs through the action of a family of enzymes called glutamine amidotransferases. These enzymes transfer NH3 from the side chain of glutamine to an appropriate substrate. There are at least fourteen different glutamine amidotransferases, each catalyzing the transfer of NH3 to a different substrate. Sequence fingerprints have been identified that assign all known glutamine amidotransferase sequences to one of two families. Neither the mechanism of NH3 generation nor the tight coupling between NH3 generation and NH3 transport are understood for any of the enzymes. This important question in biological catalysis is being addressed by determination of three-dimensional structures for three different glutamine amidotransferases in both families by X-ray crystallography. Two of the structure determinations are being done by multiwavelength anomalous diffraction and represent important new applications of this crystallographic methodology. 1. Glutamine PRPP amidotransferase catalyzes the first and committed step in de novo synthesis of purine nucleotides. Defects in the purine pathway have been associated with disorders such as hyperuricemia (gout), immunodeficiency and neurological symptoms. Crystal structures are being determined for the enzyme from both B. subtilis and E. coli in order to elucidate the function of an unusual metal center in B. subtilis and higher eukaryotes that apparently has a novel regulatory function and is not catalytic. 2. GNP synthetase, another enzyme from the purine pathway, is a target of attempts to stop cell growth, specifically tumor cell growth and T-cell proliferation. Crystals of GMP synthetase with substrate and ATP bound and crystals of enzyme alone are an excellent system for structural studies of the coupling of NH3-generating and NH3-transfer activities. 3. Imidazole glycerol 3-phosphate synthase, an enzyme from the histidine pathway, is a heterodimeric glutamine amidotransferase.