Guerin Jeremy, Botos Istvan, Zhang Zijian, Lundquist Karl, Gumbart James C, Buchanan Susan K
Laboratory of Molecular Biology, NIDDK, NIH, Bethesda, United States.
School of Physics, Georgia Institute of Technology, Atlanta, Georgia.
Elife. 2020 Oct 22;9:e58100. doi: 10.7554/eLife.58100.
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 and . 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.
细菌接触依赖性生长抑制（CDI）系统利用Vb型分泌机制，通过名为CdiB的专用外膜转运蛋白将大型CdiA毒素转运穿过外膜。在此，我们报道了来自[具体来源1]和[具体来源2]的两种CdiB转运蛋白的首个晶体结构。CdiB转运蛋白采用TpsB折叠结构，包含一个与两个周质结构域相连的16股跨膜β桶。CdiB孔道的内腔被一个N端α螺旋和保守的细胞外环6封闭；这两个元件在结构中呈现不同构象。我们在β1链上鉴定出一个保守的DxxG基序，它通过不同的相互作用网络连接环6。DxxG的结构修饰会诱导细胞外环的重排，并改变与N端α螺旋的相互作用，为α螺旋的排出做好准备。通过结构生物学、功能测定和分子动力学模拟，我们展示了桶状孔道如何为CdiA毒素分泌做好准备。
