Du Qinglin, Long Quanxin, Mao Jinxiao, Fu Tiwei, Duan Xiangke, Xie Jianping
State Key Laboratory Breeding Base of Eco-Environment and Bio-Resource of the Three Gorges Area, Key Laboratory of Eco-environments in Three Gorges Reservoir Region, Institute of Modern Biopharmaceuticals, Ministry of Education, School of Life Sciences, Southwest University, Beibei, Chongqing, China.
IUBMB Life. 2014 Jun;66(6):405-14. doi: 10.1002/iub.1277. Epub 2014 May 29.
Capreomycin (CAP) is an important second-line drug for multidrug-resistant tuberculosis. To further define the drug resistance mechanism of CAP, a Mycobacterium smegmatis transposon mutant library was constructed using Tn5 transposon for screening isolates with enhanced CAP resistance. A mutant (named C4) with fourfold increased CAP resistance was isolated and characterized. Tn5 was found to be inserted into MSMEG_0841, an annotated pseudogene. However, knockout demonstrated that MSMEG_0841 was not responsible for CAP resistance. We further sequenced the whole genome of C4 and found an A to G substitution in the overlap region between tlyA and ppnK, which leads a stop codon mutation in upstream tlyA and a T2A mutation in downstream ppnK. Mutation in the overlap might confer the dysfuction of both genes. tlyA is a known gene involved in CAP action. Overexpression of ppnK in both Escherichia coli and M. smegmatis confer subtle susceptible to CAP. Taken together, our study found that a novel mutation involved in CAP resistance.
卷曲霉素（CAP）是治疗耐多药结核病的一种重要二线药物。为进一步明确CAP的耐药机制，利用Tn5转座子构建了耻垢分枝杆菌转座子突变体文库，以筛选对CAP耐药性增强的分离株。分离并鉴定了一株对CAP耐药性增加4倍的突变体（命名为C4）。发现Tn5插入到一个注释为假基因的MSMEG_0841中。然而，基因敲除表明MSMEG_0841与CAP耐药性无关。我们进一步对C4的全基因组进行测序，发现在tlyA和ppnK的重叠区域有一个A到G的替换，这导致上游tlyA出现一个终止密码子突变，下游ppnK出现一个T2A突变。重叠区域的突变可能导致这两个基因功能失调。tlyA是一个已知的与CAP作用相关的基因。在大肠杆菌和耻垢分枝杆菌中过表达ppnK都会使它们对CAP略有敏感。综上所述，我们的研究发现了一种与CAP耐药性相关的新突变。
