Conservation of structure and activity in Plasmodium purine nucleoside phosphorylases
作者:Apirat Chaikuad、R Leo Brady
DOI:10.1186/1472-6807-9-42
日期:——
Purine nucleoside phosphorylase (PNP) is central to purine salvage mechanisms in Plasmodium parasites, the causative agents of malaria. Most human malaria results from infection either by Plasmodium falciparum (Pf), the deadliest form of the parasite, or by the widespread Plasmodium vivax (Pv). Whereas the PNP enzyme from Pf has previously been studied in detail, despite the prevalence of Pv little is known about many of the key metabolic enzymes from this parasite, including Pv PNP. The crystal structure of Pv PNP is described and is seen to have many features in common with the previously reported structure of Pf PNP. In particular, the composition and conformations of the active site regions are virtually identical. The crystal structure of a complex of Pf PNP co-crystallised with inosine and arsenate is also described, and is found to contain a mixture of products and reactants – hypoxanthine, ribose and arsenate. The ribose C1' in this hybrid complex lies close to the expected point of symmetry along the PNP reaction coordinate, consistent with a conformation between the transition and product states. These two Plasmodium PNP structures confirm the similarity of structure and mechanism of these enzymes, which are also confirmed in enzyme kinetic assays using an array of substrates. These reveal an unusual form of substrate activation by 2'-deoxyinosine of Pv PNP, but not Pf PNP. The close similarity of the Pf and Pv PNP structures allows characteristic features to be identified that differentiate the Apicomplexa PNPs from the human host enzyme. This similarity also suggests there should be a high level of cross-reactivity for compounds designed to inhibit either of these molecular targets. However, despite these similarities, there are also small differences in the activities of the two Plasmodium enzymes.
嘌呤核苷磷酸酶(PNP)是疟原虫寄生虫嘌呤回收机制的核心。大多数人类疟疾是由恶性疟原虫(Pf)或广泛传播的间日疟原虫(Pv)感染引起的。尽管之前已经对恶性疟原虫的PNP酶进行了详细研究,但人们对间日疟原虫的许多关键代谢酶知之甚少,包括间日疟原虫PNP。间日疟原虫PNP的晶体结构描述表明,它与之前报道的恶性疟原虫PNP结构有许多共同点。特别是,活性位点的组成和构象几乎完全相同。恶性疟原虫PNP与肌苷和砷酸盐共结晶的复合物的晶体结构也进行了描述,发现它包含产物和反应物(次黄嘌呤、核糖和砷酸盐)的混合物。这种混合复合物中的核糖C1'靠近PNP反应坐标轴上的预期对称点,与过渡态和产物态之间的构象一致。这两种疟原虫PNP的结构证实了这些酶的结构和机制的相似性,这也通过一系列底物的酶动力学测定得到了证实。这些结果表明,间日疟原虫PNP的2'-脱氧肌