Institute of Pathogen Biology, Chinese Academy of Medical Sciences and Peking Union Medical College, No. 9 Dong Dan San Tiao, Beijing 100730, PR China.
J Mol Biol. 2012 Apr 6;417(4):351-61. doi: 10.1016/j.jmb.2012.01.040. Epub 2012 Jan 30.
In the competition for niches in natural resources, Pseudomonas aeruginosa utilizes the type VI secretion system to inject the toxic protein effector Tse2 into bacteria on cell-cell contact. The cytoplasm toxin immunity protein Tsi2 can neutralize Tse2 by physical interaction with the toxin, providing essential protection from toxin activity. Except for orthologues in P. aeruginosa, Tsi2 antitoxin does not share detectable sequence homology with known proteins in public databases. The mechanism underlying toxin neutralization by Tsi2 remains unknown. We report here the crystal structure of Tsi2 at 2.28 Å resolution. Our structural and biophysical analyses demonstrate that the antitoxin adopts a previously unobserved superhelical conformation. Tsi2 is highly thermostable in the absence of the toxin in solution. Tsi2 assembles a dimer with 2-fold rotational symmetry, similar to that observed in other toxin-antitoxin systems. Dimerization is essential for the stable folding of Tsi2.
在自然资源小生境的竞争中，铜绿假单胞菌利用 VI 型分泌系统将毒性蛋白效应物 Tse2 注入细胞间接触的细菌中。细胞质毒素免疫蛋白 Tsi2 可以通过与毒素的物理相互作用来中和 Tse2，从而为抵御毒素活性提供必要的保护。除了铜绿假单胞菌中的同源物外，Tsi2 抗毒素与公共数据库中已知蛋白没有可检测到的序列同源性。Tsi2 中和毒素的机制尚不清楚。我们在这里报告了 Tsi2 的晶体结构，分辨率为 2.28 Å。我们的结构和生物物理分析表明，该抗毒素采用了以前未观察到的超螺旋构象。在没有毒素存在的情况下，Tsi2 在溶液中具有很高的热稳定性。Tsi2 以具有 2 重旋转对称性的二聚体形式组装，类似于在其他毒素-抗毒素系统中观察到的情况。二聚化对于 Tsi2 的稳定折叠至关重要。
