Centre for Biomedical Informatics, National Institute for Research in Tuberculosis, Chennai 600 031, Tamil Nadu, India.
Medical Biotechnology Division, School of Biosciences and Technology, VIT University, Vellore 632014, Tamil Nadu, India.
J Glob Antimicrob Resist. 2018 Dec;15:111-120. doi: 10.1016/j.jgar.2018.07.001. Epub 2018 Jul 7.
Isoniazid (INH) is still the most important first-line antitubercular drug. INH resistance is regarded as a major impediment to the tuberculosis (TB) control programme and contributes to the emergence of multidrug-resistant strains. Mutation at position 315 in the katG gene, encoding the catalase-peroxidase (KatG) enzyme, is the major cause of INH resistance in Mycobacterium tuberculosis. Therefore, investigation of the molecular mechanisms of INH resistance is the need of the hour.
To understand the clinical importance of KatG mutants (MTs) leading to INH resistance, in this study five MTs (S315T, S315I, S315R, S315N and S315G) were modelled, docked and interacted with INH in dynamic state.
The binding affinity based on docking was found to be higher for MTs than for wild-type (WT) isolates, except for MT-S315R, indicating rigid binding of INH with MT proteins compared with the flexible binding seen in the WT. Analysis of molecular dynamics (MD) experiments suggested that fluctuations and deviations were higher at the INH binding residues for MTs than for the WT. Reduction in the hydrogen bond network after MD in all KatG enzymes implies an increase in the flexibility and stability of protein structures. Superimposition of MTs upon the WT structure showed a significant deviation that varies for the different MTs.
It can be inferred that the five KatG MTs affect enzyme activity in different ways, which could be attributed to conformational changes in MT KatG that result in altered binding affinity to INH and eventually to INH resistance.
异烟肼（INH）仍然是最重要的一线抗结核药物。异烟肼耐药被认为是结核病（TB）控制规划的主要障碍，并导致多药耐药菌株的出现。编码过氧化氢酶-过氧化物酶（KatG）酶的 katG 基因第 315 位的突变是结核分枝杆菌异烟肼耐药的主要原因。因此，研究异烟肼耐药的分子机制是当务之急。
为了了解导致异烟肼耐药的 KatG 突变体（MTs）的临床重要性，本研究对 5 种 MTs（S315T、S315I、S315R、S315N 和 S315G）进行建模、对接，并在动态状态下与 INH 相互作用。
基于对接的结合亲和力发现，除了 MT-S315R 外，MTs 的结合亲和力高于野生型（WT）分离株，表明与 WT 相比，INH 与 MT 蛋白的结合更牢固。分子动力学（MD）实验分析表明，与 WT 相比，MT 蛋白在 INH 结合残基处的波动和偏差更高。所有 KatG 酶中 MD 后氢键网络的减少意味着蛋白质结构的灵活性和稳定性增加。MTs 叠加在 WT 结构上显示出明显的偏差，不同的 MTs 偏差也不同。
可以推断，五种 KatG MTs 以不同的方式影响酶活性，这可能归因于 MT KatG 的构象变化，导致与 INH 的结合亲和力改变，最终导致 INH 耐药。
