Ahmed F Hafna, Liu Jian-Wei, Royan Santana, Warden Andrew C, Esquirol Lygie, Pandey Gunjan, Newman Janet, Scott Colin, Peat Thomas S
Environment, CSIRO, Canberra, ACT, 2601, Australia.
Advanced Engineering Biology Future Science Platform, CSIRO, Canberra, ACT, 2601, Australia.
Commun Biol. 2024 Dec 19;7(1):1676. doi: 10.1038/s42003-024-07336-6.
The antibiotic 2-nitroimidazole (2NI) or azomycin, used for treating drug-resistant tuberculosis and imaging tumor hypoxia, requires activation by bacterial nitroreductases for its antibiotic and cytotoxic effect. Mycobacterium sp. JS330 produces 2-nitroimidazole nitrohydrolase (NnhA) that circumvents 2NI activation, conferring 2NI resistance by hydrolysing it to nitrite and imidazol-2-one (IM2O) instead. This study elucidates NnhA's structure, catalytic mechanism, and evolutionary background within the guanidino-group modifying enzyme (GME) superfamily, aided by a more soluble protein variant engineered through directed evolution. Despite low sequence similarity and limited occurrence in a few soil-dwelling mycobacteria and Actinomycetota, NnhA maintains the α/β propeller fold characteristic of GME superfamily enzymes and forms an unusual hexameric ring structure formed by a trimer of domain-swapped dimers. The similarity of its active site to arginine deiminases (ADIs) and human dimethylarginine dimethylaminohydrolases (DDAHs), along with molecular dynamics simulations, suggests NnhA's catalytic mechanism resembles the hydrolysis reactions of these related enzymes.
抗生素2-硝基咪唑（2NI）或偶氮霉素，用于治疗耐药结核病和成像肿瘤缺氧，其抗生素和细胞毒性作用需要细菌硝基还原酶激活。分枝杆菌属JS330产生2-硝基咪唑硝基水解酶（NnhA），该酶绕过2NI激活，通过将其水解为亚硝酸盐和咪唑-2-酮（IM2O）赋予2NI抗性。本研究借助通过定向进化设计的更易溶的蛋白质变体，阐明了NnhA在胍基修饰酶（GME）超家族中的结构、催化机制和进化背景。尽管NnhA序列相似性低，且仅在少数土壤栖居分枝杆菌和放线菌门中出现，但它保持了GME超家族酶特有的α/β螺旋桨折叠，并形成了由结构域交换二聚体三聚体组成的不寻常六聚体环结构。其活性位点与精氨酸脱亚氨酶（ADI）和人二甲基精氨酸二甲胺水解酶（DDAH）的相似性，以及分子动力学模拟表明，NnhA的催化机制类似于这些相关酶的水解反应。
