Eaazhisai K, Jayalakshmi R, Gayathri P, Anand R P, Sumathy K, Balaram H, Murthy M R N
Molecular Biophysics Unit, UGC Centre of Advanced Study, Indian Institute of Science, Bangalore 560012, India.
J Mol Biol. 2004 Jan 30;335(5):1251-64. doi: 10.1016/j.jmb.2003.11.036.
In the absence of the de novo purine nucleotide biosynthetic pathway in parasitic protozoa, purine salvage is of primary importance for parasite survival. Enzymes of the salvage pathway are, therefore, good targets for anti-parasitic drugs. Adenylosuccinate synthetase (AdSS), catalysing the first committed step in the synthesis of AMP from IMP, is a potential target for anti-protozoal chemotherapy. We report here the crystal structure of adenylosuccinate synthetase from the malaria parasite, Plasmodium falciparum, complexed to 6-phosphoryl IMP, GDP, Mg2+ and the aspartate analogue, hadacidin at 2 A resolution. The overall architecture of P. falciparum AdSS (PfAdSS) is similar to the known structures from Escherichia coli, mouse and plants. Differences in substrate interactions seen in this structure provide a plausible explanation for the kinetic differences between PfAdSS and the enzyme from other species. Additional hydrogen bonding interactions of the protein with GDP may account for the ordered binding of substrates to the enzyme. The dimer interface of PfAdSS is also different, with a pronounced excess of positively charged residues. Differences highlighted here provide a basis for the design of species-specific inhibitors of the enzyme.
由于寄生原生动物缺乏嘌呤核苷酸从头合成途径，嘌呤补救途径对于寄生虫的生存至关重要。因此，补救途径的酶是抗寄生虫药物的良好靶点。腺苷酸琥珀酸合成酶（AdSS）催化从肌苷酸（IMP）合成腺苷酸（AMP）的第一步关键反应，是抗原生动物化疗的一个潜在靶点。我们在此报告了来自疟原虫恶性疟原虫的腺苷酸琥珀酸合成酶的晶体结构，该结构与6-磷酸化IMP、鸟苷二磷酸（GDP）、镁离子（Mg2+）以及天冬氨酸类似物重氮丝氨酸在2埃分辨率下形成复合物。恶性疟原虫AdSS（PfAdSS）的整体结构与来自大肠杆菌、小鼠和植物的已知结构相似。在此结构中观察到的底物相互作用差异为PfAdSS与其他物种的酶之间的动力学差异提供了合理的解释。蛋白质与GDP的额外氢键相互作用可能解释了底物与酶的有序结合。PfAdSS的二聚体界面也有所不同，带有明显过量的带正电残基。此处突出显示的差异为设计该酶的物种特异性抑制剂提供了基础。
