Structural insight into toxin secretion by contact-dependent growth inhibition transporters.
Structural insight into toxin secretion by contact-dependent growth inhibition transporters.
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DOI：
10.7554/elife.58100
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发表时间：
2020-10-22
期刊：
影响因子：
7.7
通讯作者：
Buchanan SK
中科院分区：
文献类型：
--
作者：
Guerin J;Botos I;Zhang Z;Lundquist K;Gumbart JC;Buchanan SK
细菌接触依赖性生长抑制（CDI）系统使用Vb型分泌机制通过称为CdiB的专用外膜转运蛋白将大的CdiA毒素输出穿过外膜。在这里，我们报告的第一个晶体结构的两个CdiB转运鲍曼不动杆菌和大肠杆菌。CdiB转运蛋白采用TpsB折叠，含有连接到两个周质结构域的16链跨膜β-桶。CdiB孔的内腔被N-末端α-螺旋和保守的细胞外环6堵塞;这两个元件在结构中采用不同的构象。我们鉴定了位于链β1上的保守DxxG基序，其通过不同的相互作用网络连接环6。DxxG的结构修饰诱导细胞外环的重排，并改变与N-末端α-螺旋的相互作用，使系统为α-螺旋排出做好准备。使用结构生物学，功能测定和分子动力学模拟，我们展示了桶孔是如何启动CdiA毒素分泌的。
Bacterial contact-dependent growth inhibition (CDI) systems use a type Vb secretion mechanism to export large CdiA toxins across the outer membrane by dedicated outer membrane transporters called CdiB. Here, we report the first crystal structures of two CdiB transporters from Acinetobacter baumannii and Escherichia coli. CdiB transporters adopt a TpsB fold, containing a 16-stranded transmembrane β-barrel connected to two periplasmic domains. The lumen of the CdiB pore is occluded by an N-terminal α-helix and the conserved extracellular loop 6; these two elements adopt different conformations in the structures. We identified a conserved DxxG motif located on strand β1 that connects loop 6 through different networks of interactions. Structural modifications of DxxG induce rearrangement of extracellular loops and alter interactions with the N-terminal α-helix, preparing the system for α-helix ejection. Using structural biology, functional assays, and molecular dynamics simulations, we show how the barrel pore is primed for CdiA toxin secretion.