Master S S, Springer B, Sander P, Boettger E C, Deretic V, Timmins G S
Department of Molecular Genetics and Microbiology1 and Department of Pharmacy2, University of New Mexico Health Sciences Center, 915 Camino de Salud, Albuquerque, NM 87131, USA.
Institute for Medical Microbiology, Medizinische Hochschule, 30625, Hannover, Germany3.
Microbiology (Reading). 2002 Oct;148(Pt 10):3139-3144. doi: 10.1099/00221287-148-10-3139.
The Mycobacterium tuberculosis ahpC gene, encoding the mycobacterial orthologue of alkylhydroperoxide reductase, undergoes an unusual regulatory cycle. The levels of AhpC alternate between stages of expression silencing in virulent strains grown as aerated cultures, secondary to a natural loss of the regulatory oxyR function in all strains of the tubercle bacillus, and expression activation in static bacilli by a yet undefined mechanism. The reasons for this unorthodox regulatory cycle controlling expression of an antioxidant factor are currently not known. In this work, M. tuberculosis H37Rv and Mycobacterium smegmatis mc(2)155 ahpC knockout mutants were tested for sensitivity to reactive nitrogen intermediates, in particular peroxynitrite, a highly reactive combinatorial product of reactive nitrogen and oxygen species, and sensitivity to bactericidal mechanisms in resting and activated macrophages. Both M. tuberculosis ahpC::Km(r) and M. smegmatis ahpC::Km(r) showed increased susceptibility to peroxynitrite. In contrast, inactivation of ahpC in M. tuberculosis did not cause increased sensitivity to donors of NO alone. M. tuberculosis ahpC::Km(r) also showed decreased survival in unstimulated macrophages, but the effect was no longer detectable upon IFNgamma activation. These studies establish a specific role for ahpC in antioxidant defences involving peroxynitrite and most likely additional cidal mechanisms in macrophages, with the regulatory cycle likely contributing to survival upon coming out of the stationary phase during dormancy (latent infection) or upon transmission to a new host.
结核分枝杆菌的ahpC基因编码烷基过氧化氢还原酶的分枝杆菌同源物，其经历一个不同寻常的调控周期。在通气培养的有毒菌株中，AhpC水平在表达沉默阶段之间交替变化，这是由于结核杆菌所有菌株中调控性氧还蛋白（OxyR）功能的自然丧失所致；而在静止的杆菌中，AhpC通过一种尚未明确的机制被激活表达。目前尚不清楚这种控制抗氧化因子表达的非正统调控周期的原因。在这项研究中，对结核分枝杆菌H37Rv和耻垢分枝杆菌mc(2)155的ahpC基因敲除突变体进行了对活性氮中间体，特别是过氧亚硝酸盐（一种活性氮和氧物种的高反应性组合产物）的敏感性测试，以及对静息和活化巨噬细胞中杀菌机制的敏感性测试。结核分枝杆菌ahpC::Km(r)和耻垢分枝杆菌ahpC::Km(r)对过氧亚硝酸盐的敏感性均增加。相比之下，结核分枝杆菌中ahpC的失活并未导致对单独的一氧化氮供体的敏感性增加。结核分枝杆菌ahpC::Km(r)在未刺激的巨噬细胞中的存活率也降低，但在γ干扰素激活后这种效应不再可检测到。这些研究确定了ahpC在涉及过氧亚硝酸盐的抗氧化防御中的特定作用，并且很可能在巨噬细胞中还有其他杀菌机制，这种调控周期可能有助于在休眠（潜伏感染）期间从静止期出来或传播到新宿主时的存活。
