Cryo-EM structures reveal translocational unfolding in the clostridial binary iota toxin complex
Cryo-EM structures reveal translocational unfolding in the clostridial binary iota toxin complex
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DOI：
10.1038/s41594-020-0388-6
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发表时间：
2020-03-02
影响因子：
16.8
通讯作者：
Tsuge, Hideaki
中科院分区：
文献类型：
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作者：
Yamada, Tomohito;Yoshida, Toru;Tsuge, Hideaki
E 型产气荚膜梭菌产生的 iota 毒素是一种二元毒素，包含两个独立的多肽：Ia（一种 ADP-核糖基转移酶）和 Ib（参与细胞结合和 Ia 跨细胞膜易位）。在这里，我们报道了易位通道 Ib 孔及其与 Ia 的复合物的冷冻电镜结构。高分辨率 Ib 孔结构展示了与炭疽保护性抗原孔的催化 phi-clamp 类似的结构框架。然而，Ia 结合的 Ib 孔结构显示出一种独特的 Ia 结合模式：一个 Ia 与 Ib 孔结合，并且 Ia 氨基末端结构域与另外两个 Ib 孔收缩位点形成多个弱相互作用。此外，Ib 结合诱导 Ia N 端 α 螺旋倾斜和部分展开，使其延伸至 phi-clamp 门。这种 N 端展开的新机制对于蛋白质易位至关重要。对二元 Iota 毒素 Ib 及其毒性亚基 Ia 的孔形式的结构阐明，可视化介导 Ia 易位通过孔的相互作用以及 Ia N 端的延伸，这与布朗棘轮易位机制一致。
The iota toxin produced by Clostridium perfringens type E is a binary toxin comprising two independent polypeptides: Ia, an ADP-ribosyltransferase, and Ib, which is involved in cell binding and translocation of Ia across the cell membrane. Here we report cryo-EM structures of the translocation channel Ib-pore and its complex with Ia. The high-resolution Ib-pore structure demonstrates a similar structural framework to that of the catalytic phi-clamp of the anthrax protective antigen pore. However, the Ia-bound Ib-pore structure shows a unique binding mode of Ia: one Ia binds to the Ib-pore, and the Ia amino-terminal domain forms multiple weak interactions with two additional Ib-pore constriction sites. Furthermore, Ib-binding induces tilting and partial unfolding of the Ia N-terminal alpha-helix, permitting its extension to the phi-clamp gate. This new mechanism of N-terminal unfolding is crucial for protein translocation.Structural elucidation of the pore form of binary Iota toxin Ib with its toxic subunit, Ia, visualizes interactions mediating Ia translocation through the pore and extension of the Ia N-terminus consistent with a Brownian ratchet translocation mechanism.