9WSZ

CryoEM structure of baseplate iris structure in the contracted AlgoCIS

Summary for 9WSZ

• Entry DOI: 10.2210/pdb9wsz/pdb
• EMDB information: 66211
• Descriptor: Baseplate protein Alg12, Baseplate protein J-like domain-containing protein (2 entities in total)
• Functional Keywords: contractile injection system, cryoem, marine bacterium, structural protein
• Biological source: Algoriphagus machipongonensis; More
• Total number of polymer chains: 12
• Total formula weight: 1355578.82

Authors

Xu, J.,Ericson, C.F.,Toenshoff, E.R.,Pilhofer, M. (deposition date: 2025-09-15, release date: 2026-05-06)

Primary citation

Xu, J.,Ericson, C.F.,Toenshoff, E.R.,Pilhofer, M.
Stepwise firing mechanism of an extracellular contractile injection system.
Nat Commun, 2026

PubMed 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 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.

PubMed: 42031783
DOI: 10.1038/s41467-026-72240-y

Experimental method

ELECTRON MICROSCOPY (3.7 Å)