Marney Matthew W, Metzger Robert P, Hecht David, Valafar Faramarz
Department of Chemistry and Biochemistry, San Diego State University, San Diego, CA 92182-1030, USA.
Department of Chemistry and Biochemistry, San Diego State University, San Diego, CA 92182-1030, USA; Department of Chemistry, Southwestern College, Chula Vista, CA 91910, USA.
Tuberculosis (Edinb). 2018 Jan;108:155-162. doi: 10.1016/j.tube.2017.11.007. Epub 2017 Nov 22.
WHO reported 10.4 million new tuberculosis (TB) cases and 1.8 million deaths in 2015, making M. tuberculosis the most successful human pathogen with highest mortality among infectious diseases [1,2]. Drug-resistant TB is a major threat to global TB control [2,3]. Recently Torres et al. [4] identified 14 novel substitutions in M. tuberculosis-KatG (the enzyme associated with resistance to isoniazid-an important first-line anti-TB drug) and demonstrated that 12 of the 14 can cause INH-resistance in M. smegmatis. This study presents an in silico structure-based analysis of these 14 amino acid substitutions using homology models and x-ray crystal structures (when available) in M. tuberculosis. Our models demonstrate that several of these mutations cluster around three openings in the KatG tertiary structure which appear to initiate channels to the heme group at the catalytic center of the enzyme. We studied the effects of these mutations on the tertiary structure of KatG, focusing on conformational changes in the three channels in the protein structure. Our results suggest that the 14 novel mutations sufficiently restrict one or more of these access channels, thus potentially preventing INH from reaching the catalytic heme. These observations provide valuable insights into the structure-based origins of INH resistance and provide testable hypotheses for future experimental studies.
世界卫生组织报告称，2015年有1040万新发结核病病例，180万人死亡，这使得结核分枝杆菌成为最成功的人类病原体，在传染病中死亡率最高[1,2]。耐多药结核病是全球结核病控制的主要威胁[2,3]。最近，托雷斯等人[4]在结核分枝杆菌KatG（与对异烟肼——一种重要的一线抗结核药物的耐药性相关的酶）中鉴定出14个新的替换位点，并证明这14个位点中的12个可导致耻垢分枝杆菌对异烟肼产生耐药性。本研究利用结核分枝杆菌的同源模型和X射线晶体结构（如有），对这14个氨基酸替换进行了基于计算机模拟结构的分析。我们的模型表明，其中几个突变聚集在KatG三级结构的三个开口周围，这些开口似乎通向该酶催化中心的血红素基团。我们研究了这些突变对KatG三级结构的影响，重点关注蛋白质结构中三个通道的构象变化。我们的结果表明，这14个新突变充分限制了这些通道中的一个或多个，从而可能阻止异烟肼到达催化血红素。这些观察结果为异烟肼耐药性的基于结构的起源提供了有价值的见解，并为未来的实验研究提供了可检验的假设。
