Kim Jin-Sik, Song Saemee, Lee Minho, Lee Seunghwa, Lee Kangseok, Ha Nam-Chul
Department of Agricultural Biotechnology, Center for Food Safety and Toxicology, Center for Food and Bioconvergence, Research Institute for Agricultural and Life Sciences, Seoul National University, Room #200-1041, 1 Gwanak-ro, Gwanak-gu, Seoul 151-921, Republic of Korea.
Department of Life Science, Chung-Ang University, Seoul, 156-756 Republic of Korea.
Structure. 2016 Mar 1;24(3):477-85. doi: 10.1016/j.str.2015.12.012. Epub 2016 Jan 28.
The protein toxin HlyA of Escherichia coli is exported without a periplasmic intermediate by the type I secretion system (T1SS). The T1SS is composed of an inner membrane ABC transporter HlyB, an outer-membrane channel protein TolC, and a membrane fusion protein HlyD. However, the assembly of the T1SS remains to be elucidated. In this study, we determine the crystal structure of a part of the C-terminal periplasmic domain of HlyD. The long α-helical domain consisting of three α helices and a lipoyl domain was identified in the crystal structure. Based on the HlyD structure, we modeled the hexameric assembly of HlyD with a long α-helical barrel, which formed a complex with TolC in an intermeshing cogwheel-to-cogwheel manner, as observed in tripartite RND-type drug efflux pumps. These observations provide a structural blueprint for understanding the type I secretion system in pathogenic Gram-negative bacteria.
大肠杆菌的蛋白质毒素HlyA通过I型分泌系统（T1SS）在没有周质中间体的情况下输出。T1SS由内膜ABC转运蛋白HlyB、外膜通道蛋白TolC和膜融合蛋白HlyD组成。然而，T1SS的组装仍有待阐明。在本研究中，我们确定了HlyD C端周质结构域一部分的晶体结构。在晶体结构中鉴定出由三个α螺旋和一个硫辛酰结构域组成的长α螺旋结构域。基于HlyD结构，我们构建了具有长α螺旋桶的HlyD六聚体组装模型，该模型与TolC以相互啮合的齿轮对齿轮方式形成复合物，这在三方RND型药物外排泵中也有观察到。这些观察结果为理解致病性革兰氏阴性菌中的I型分泌系统提供了结构蓝图。
