PURINE/PYRIMIDINE METABOLISM IN TRICHOMONAS AND GIARDIA

滴虫病和贾第鞭毛虫病是我国最常见的两种寄生虫病。 世界。缺乏有效的化学预防和化疗 今天对它们的控制是非常令人担忧的。我们最近表示 滴虫和贾第虫都不能从头合成 嘌呤和嘧啶核苷酸，它们可能构成主要的 对他们来说很脆弱。几种主要的、不可或缺的抢救酶有 在这些寄生虫中被发现，其中包括T.fotus IMP 脱氢酶，胎儿次黄嘌呤-鸟嘌呤-黄嘌呤 磷酸核糖基转移酶和蓝藻鸟嘌呤磷酸核糖基转移酶 每一种都被提纯到同质并进行了表征。三个都是 酶表现出独特的动力学性质和独特的底物 可能使其成为化疗靶点的特异性。 动力学同位素效应和同位素交换的进一步研究 将对胎儿进行IMP脱氢酶检测，以进一步了解 酶催化反应的机理及酶的特殊性质 它的二核苷酸结合位点。编码这三种酶的基因将是 聚合酶链式反应鉴定、克隆、测序和表达 在细菌、酵母、哺乳动物细胞或杆状病毒中获得高产 天然蛋白质。由此生产和纯化的重组酶将 关于酶催化的详细机理，请进一步分析。他们的 将分析从编码DNA序列派生的一级结构 通过计算机建模和定点突变相结合的方法 三级蛋白质结构的阐明。在长远的未来规划中， 纯净的蛋白质将被结晶，用于X射线衍射分析 蛋白质的三维结构及其结构比较 用于特定抑制剂设计的结构-功能关系。一个 次黄嘌呤/鸟嘌呤转运蛋白是最近在胎儿弓形虫中发现的。它 显然对这种寄生虫在野生型中的生存是必不可少的。 我们将尝试通过抑制剂研究来鉴定转运蛋白并分离 这种转运蛋白通过光亲和标记而发展成为一个新的靶点 未来的抗滴虫化疗。

Trichomoniasis and giardiasis are two prevalent parasitic diseases in the world. The lack of effective chemoprophylactic and chemotherapeutic controls of them today are of great concern. We have recently indicated that Trichomonas and Giardia are both incapable of de novo synthesis of purine and pyrimidine nucleotides, which may constitute a major vulnerability for them. Several major, indispensable salvage enzymes have since been identified in these parasites, among which T. foetus IMP dehydrogenase, T. foetus hypoxanthanine-guanine-xanthine phosphoribosyltransferase and G. lamblia guanine phosphoribosyltransferase have been each purified to homogeneity and characterized. All three enzymes demonstrated unique kinetic properties and distinctive substrate specificities which may quality them as the chemotherapeutic targets. Further studies of the kinetic isotope effects and the isotope exchange on T. foetus IMP dehydrogenase will be performed for more understanding on the mechanism of the enzyme-catalyzed reaction and the unusual properties of its dinucleotide binding site. Genes encoding these three enzymes will be identified by polymerase chain reactions, cloned, sequenced and expressed in bacteria, yeast, mammalian cells or baculovirus for high yields of native proteins. The recombinant enzymes thus produced and purified will be further analyzed for detailed mechanisms of enzyme catalysis. Their primary structures derived from the encoding DNA sequences will be analyzed by computer modelings coupled with site-directed mutagenesis for elucidation of tertiary protein structures. In the long-term future plan, pure proteins will be crystallized for X-ray diffraction analysis of the three dimensional structures and comparisons among the protein structures for structure-function relationships for specific inhibitor designs. A hypoxanthine/guanine transporter was recently identified in T. foetus. It is apparently essential for the survival of this parasite in its wild-type. We will try to identify the transporter by inhibitor studies and isolate this transporter by photoaffinity labeling and develop it as a new target of anti-trichomonial chemotherapy for the future.