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首页> 美国卫生研究院文献>Proceedings of the National Academy of Sciences of the United States of America >PNAS Plus: VgrG C terminus confers the type VI effector transport specificity and is required for binding with PAAR and adaptor–effector complex
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PNAS Plus: VgrG C terminus confers the type VI effector transport specificity and is required for binding with PAAR and adaptor–effector complex

机译：PNAS Plus：VgrG C末端赋予VI型效应子转运特异性是与PAAR和衔接子-效应子复合体结合所必需的

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Type VI secretion system (T6SS) is a macromolecular machine used by many Gram-negative bacteria to inject effectors/toxins into eukaryotic hosts or prokaryotic competitors for survival and fitness. To date, our knowledge of the molecular determinants and mechanisms underlying the transport of these effectors remains limited. Here, we report that two T6SS encoded valine-glycine repeat protein G (VgrG) paralogs in Agrobacterium tumefaciens C58 specifically control the secretion and interbacterial competition activity of the type VI DNase toxins Tde1 and Tde2. Deletion and domain-swapping analysis identified that the C-terminal extension of VgrG1 specifically confers Tde1 secretion and Tde1-dependent interbacterial competition activity in planta, and the C-terminal variable region of VgrG2 governs this specificity for Tde2. Functional studies of VgrG1 and VgrG2 variants with stepwise deletion of the C terminus revealed that the C-terminal 31 aa (C31) of VgrG1 and 8 aa (C8) of VgrG2 are the molecular determinants specifically required for delivery of each cognate Tde toxin. Further in-depth studies on Tde toxin delivery mechanisms revealed that VgrG1 interacts with the adaptor/chaperone–effector complex (Tap-1–Tde1) in the absence of proline-alanine-alanine-arginine (PAAR) and the VgrG1–PAAR complex forms independent of Tap-1 and Tde1. Importantly, we identified the regions involved in these interactions. Although the entire C31 segment is required for binding with the Tap-1–Tde1 complex, only the first 15 aa of this region are necessary for PAAR binding. These results suggest that the VgrG1 C terminus interacts sequentially or simultaneously with the Tap-1–Tde1 complex and PAAR to govern Tde1 translocation across bacterial membranes and delivery into target cells for antibacterial activity.
机译：VI型分泌系统（T6SS）是许多革兰氏阴性细菌用来将效应子/毒素注入真核宿主或原核竞争者中以维持生存和适应性的大分子机器。迄今为止，我们对这些效应子运输的分子决定因素和机制的了解仍然有限。在这里，我们报告两个根癌农杆菌C58中的T6SS编码的缬氨酸-甘氨酸重复蛋白G（VgrG）旁系同源物专门控制VI型DNase毒素Tde1和Tde2的分泌和细菌间竞争活性。缺失和结构域交换分析表明，VgrG1的C端延伸特别赋予植物Tde1分泌和依赖Tde1的细菌竞争活性，而VgrG2的C端可变区控制着Tde2的这种特异性。对VgrG1和VgrG2变体进行C末端逐步缺失的功能研究表明，VgrG1的C末端31 aa（C31）和VgrG2的8 aa（C8）是传递每种同源Tde毒素所需的分子决定簇。对Tde毒素传递机制的进一步深入研究表明，在缺乏脯氨酸-丙氨酸-丙氨酸-精氨酸（PAAR）和VgrG1-PAAR复杂形式的情况下，VgrG1与衔接子/伴侣-效应子复合物（Tap-1–Tde1）相互作用。独立于Tap-1和Tde1。重要的是，我们确定了这些交互作用所涉及的区域。尽管与Tap-1–Tde1复合物结合需要完整的C31片段，但PAAR结合仅需要该区域的前15个氨基酸。这些结果表明，VgrG1 C末端与Tap-1–Tde1复合体和PAAR顺序或同时相互作用，以控制Tde1在细菌膜上的移位并传递至靶细胞以产生抗菌活性。

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