Stepwise acquisition of pyrimethamine resistance in the malaria parasite
Stepwise acquisition of pyrimethamine resistance in the malaria parasite
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DOI：
10.1073/pnas.0905922106
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发表时间：
2009-07-21
影响因子：
11.1
通讯作者：
Hartl, Daniel L.
中科院分区：
文献类型：
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作者：
Lozovsky, Elena R.;Chookajorn, Thanat;Hartl, Daniel L.
高水平乙胺嘧啶耐药性在非洲的传播威胁着抗叶酸抗疟疾药物的治疗寿命。我们采用了一种方法，即所有可能的突变中间产物都是通过定点突变产生的，并检测它们的耐药性水平，从而研究了乙胺嘧啶耐药性进化中的可能进化途径。对恶性疟原虫二氢叶酸还原酶(DHFR)的编码序列进行了突变，并在大肠杆菌中进行了选择性抑制内源性细菌酶的试验。我们研究了与乙胺嘧啶耐药有关的4个关键氨基酸替换：N51I、C59R、S108N和I164L。利用对恶性疟原虫突变谱和基于相对耐药性水平的固定概率的经验估计，我们发现预测的耐药途径与以前的动力学研究中报道的以及在自然种群中观察到的DHFR基因多态是一致的。我们发现，在乙胺嘧啶抗性进化的模拟实现中，这3条途径占到了近90%。最常见的途径(S108N，然后是C59R、N51I和I164L)占模拟实现的一半以上。我们的结果也解释了为什么I164L在东南亚和南美被检测到，但在非洲没有显著的频率。
The spread of high-level pyrimethamine resistance in Africa threatens to curtail the therapeutic lifetime of antifolate antimalarials. We studied the possible evolutionary pathways in the evolution of pyrimethamine resistance using an approach in which all possible mutational intermediates were created by site-directed mutagenesis and assayed for their level of drug resistance. The coding sequence for dihydrofolate reductase (DHFR) from the malaria parasite Plasmodium falciparum was mutagenized, and tests were carried out in Escherichia coli under conditions in which the endogenous bacterial enzyme was selectively inhibited. We studied 4 key amino acid replacements implicated in pyrimethamine resistance: N51I, C59R, S108N, and I164L. Using empirical estimates of the mutational spectrum in P. falciparum and probabilities of fixation based on the relative levels of resistance, we found that the predicted favored pathways of drug resistance are consistent with those reported in previous kinetic studies, as well as DHFR polymorphisms observed in natural populations. We found that 3 pathways account for nearly 90% of the simulated realizations of the evolution of pyrimethamine resistance. The most frequent pathway (S108N and then C59R, N51I, and I164L) accounts for more than half of the simulated realizations. Our results also suggest an explanation for why I164L is detected in Southeast Asia and South America, but not at significant frequencies in Africa.