Cryo-EM structures reveal translocational unfolding in the clostridial binary iota toxin complex.,Nature Structural & Molecular Biology

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Cryo-EM structures reveal translocational unfolding in the clostridial binary iota toxin complex.
Nature Structural & Molecular Biology ( IF 12.5 ) Pub Date : 2020-03-02 , DOI: 10.1038/s41594-020-0388-6
Tomohito Yamada ₁ , Toru Yoshida _{1,

2} , Akihiro Kawamoto ₃ , Kaoru Mitsuoka ₄ , Kenji Iwasaki _{3,

5} , Hideaki Tsuge _{1,

2,

6}

Affiliation

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 ϕ-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 α-helix, permitting its extension to the ϕ-clamp gate. This new mechanism of N-terminal unfolding is crucial for protein translocation.

中文翻译：

低温电磁结构揭示了梭菌二元碘毒素复合物中的易位展开。

E型产气荚膜梭菌产生的iota毒素是一种二进制毒素，包含两个独立的多肽：Ia，ADP-核糖基转移酶和Ib，它参与细胞结合和Ia跨细胞膜的转运。在这里，我们报告易位通道Ib孔及其与Ia的复合体的冷冻EM结构。高分辨率的Ib孔结构显示出与炭疽保护性抗原孔的催化ϕ夹相似的结构框架。但是，与Ia结合的Ib孔结构显示了Ia的独特结合方式：一个Ia与Ib孔结合，并且Ia氨基末端结构域与另外两个Ib孔收缩位点形成了多个弱相互作用。此外，Ib结合引起Ia N端α螺旋的倾斜和部分展开，从而使其延伸至ϕ夹门。

更新日期：2020-03-02

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