Journal: Nat Commun / Year: 2026 Title: Stepwise firing mechanism of an extracellular contractile injection system. Authors: Jingwei Xu / Charles F Ericson / Elena R Toenshoff / Martin Pilhofer / Abstract: Contractile injection systems (CISs) mediate cell-cell interactions and are widespread among bacteria and archaea. These phage tail-like macromolecular machines puncture their target by a tube that ...Contractile injection systems (CISs) mediate cell-cell interactions and are widespread among bacteria and archaea. These phage tail-like macromolecular machines puncture their target by a tube that is propelled by a contractile sheath. The mechanism underlying CIS firing, which starts with target binding and ends with sheath contraction, remains unclear. Here, we investigate the extracellular CIS from Algoriphagus machipongonensis (AlgoCIS) by a multimodal cryo-electron microscopy approach and structure-guided engineering, which allowed us to arrest AlgoCIS in multiple intermediate states of firing. Together with the post-firing structure, our data suggest a stepwise firing mechanism involving all structural modules: signal propagation starts with the binding of the tail-fibers, followed by opening of the cage, an expansion of the baseplate iris, and resulting in sheath contraction and the release of cap adaptor. Our study will serve as a framework for understanding the firing mechanism of diverse CISs and will facilitate the engineering of CISs for biomedical applications.
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Algoriphagus machipongonensis (bacteria)
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Switzerland, European Union, 4 items 
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