Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, Illinois 60637, USA.
Biochemistry. 2010 Mar 16;49(10):2205-15. doi: 10.1021/bi902133s.
Toxin-antitoxin (TA) systems form a ubiquitous class of prokaryotic proteins with functional roles in plasmid inheritance, environmental stress response, and cell development. ParDE family TA systems are broadly conserved on plasmids and bacterial chromosomes and have been well characterized as genetic elements that promote stable plasmid inheritance. We present a crystal structure of a chromosomally encoded ParD-ParE complex from Caulobacter crescentus at 2.6 A resolution. This TA system forms an alpha(2)beta(2) heterotetramer in the crystal and in solution. The toxin-antitoxin binding interface reveals extensive polar and hydrophobic contacts of ParD antitoxin helices with a conserved recognition and binding groove on the ParE toxin. A cross-species comparison of this complex structure with related toxin structures identified an antitoxin recognition and binding subdomain that is conserved between distantly related members of the RelE/ParE toxin superfamily despite a low level of overall primary sequence identity. We further demonstrate that ParD antitoxin is dimeric, stably folded, and largely helical when not bound to ParE toxin. Thus, the paradigmatic model in which antitoxin undergoes a disorder-to-order transition upon toxin binding does not apply to this chromosomal ParD-ParE TA system.
毒素-抗毒素 (TA) 系统是一类普遍存在的原核蛋白，在质粒遗传、环境应激反应和细胞发育中具有功能作用。ParDE 家族 TA 系统在质粒和细菌染色体上广泛保守，并被很好地表征为促进稳定质粒遗传的遗传元件。我们展示了来自新月柄杆菌的染色体编码 ParD-ParE 复合物的晶体结构，分辨率为 2.6Å。该 TA 系统在晶体和溶液中形成一个 alpha(2)beta(2) 异源四聚体。毒素-抗毒素结合界面揭示了 ParD 抗毒素螺旋与 ParE 毒素上保守的识别和结合槽之间广泛的极性和疏水性接触。对该复合物结构与相关毒素结构的跨物种比较表明，尽管整体一级序列同一性较低，但在远缘的 RelE/ParE 毒素超家族成员之间存在保守的抗毒素识别和结合亚结构。我们进一步证明，当不与 ParE 毒素结合时，ParD 抗毒素是二聚体，稳定折叠，并且主要是螺旋的。因此，抗毒素在毒素结合时经历无序到有序的转变的典范模型不适用于这种染色体 ParD-ParE TA 系统。
