ABSTRACT
The mechanistic basis for the resistance of
Mycobacterium tuberculosis
to
para
-aminosalicylic acid (PAS), an important agent in the treatment of multidrug-resistant tuberculosis, has yet to be fully defined. As a substrate analog of the folate precursor
para
-aminobenzoic acid, PAS is ultimately bioactivated to hydroxy dihydrofolate, which inhibits dihydrofolate reductase and disrupts the operation of folate-dependent metabolic pathways. As a result, the mutation of dihydrofolate synthase, an enzyme needed for the bioactivation of PAS, causes PAS resistance in
M. tuberculosis
strain H37Rv. Here, we demonstrate that various missense mutations within the coding sequence of the dihydropteroate (H
2
Pte) binding pocket of dihydrofolate synthase (FolC) confer PAS resistance in laboratory isolates of
M. tuberculosis
and
Mycobacterium bovis
. From a panel of 85 multidrug-resistant
M. tuberculosis
clinical isolates, 5 were found to harbor mutations in the
folC
gene within the H
2
Pte binding pocket, resulting in PAS resistance. While these alterations in the H
2
Pte binding pocket resulted in reduced dihydrofolate synthase activity, they also abolished the bioactivation of hydroxy dihydropteroate to hydroxy dihydrofolate. Consistent with this model for abolished bioactivation, the introduction of a wild-type copy of
folC
fully restored PAS susceptibility in
folC
mutant strains. Confirmation of this novel PAS resistance mechanism will be beneficial for the development of molecular method-based diagnostics for
M. tuberculosis
clinical isolates and for further defining the mode of action of this important tuberculosis drug.
摘要
结核分枝杆菌耐药性的机理基础
结核分枝杆菌
对
对氨基水杨酸(PAS
-对氨基水杨酸(PAS)产生耐药性的机理基础尚未完全明确,而对氨基水杨酸是治疗耐多药结核病的一种重要药物。作为叶酸前体的底物类似物
对
-作为叶酸前体对氨基苯甲酸的底物类似物,PAS 最终会被生物活化为羟基二氢叶酸,从而抑制二氢叶酸还原酶,破坏叶酸依赖性代谢途径的运行。因此,PAS 的生物活化所需的二氢叶酸合成酶发生突变,会导致结核杆菌对 PAS 产生抗药性。
结核杆菌
菌株 H37Rv 对 PAS 的耐药性。在这里,我们证明了二氢叶酸(H
2
Pte)结合口袋中的各种错义突变使实验室分离的结核杆菌对 PAS 产生抗性。
结核杆菌
和
牛分枝杆菌
.从一组 85 个耐多药
结核分枝杆菌
临床分离株中,发现有 5 株的
folC
基因突变。
2
Pte 结合袋中的 folC 基因发生突变,导致对 PAS 产生抗药性。虽然这些 H
2
Pte 结合袋中的这些改变导致二氢叶酸合成酶活性降低,同时也取消了将羟基二氢蝶酸转化为羟基二氢叶酸的生物活化作用。与废除生物活化的这一模式相一致,引入一个野生型拷贝的
folC
完全恢复了
folC
突变株对 PAS 的敏感性。这种新型 PAS 抗性机理的确认将有助于开发基于分子方法的结核杆菌诊断方法。
结核杆菌
临床分离株的基于分子方法的诊断,并进一步确定这种重要结核病药物的作用模式。