9WXF

cryo-electron microscopy structure of Dandelion

Summary for 9WXF

• Entry DOI: 10.2210/pdb9wxf/pdb
• EMDB information: 66345
• Descriptor: Dandelion (1 entity in total)
• Functional Keywords: dodecamer, immune system
• Biological source: Escherichia coli
• Total number of polymer chains: 12
• Total formula weight: 644988.74

Authors

Yu, Y.,Chen, Q.,Tang, Y. (deposition date: 2025-09-25, release date: 2026-07-08)

Primary citation

Tang, Y.,Liu, T.,Xiong, C.,Chen, Q.,Yu, Y.
Oligomer disassembly activates an HEPN-containing bacterial defense system.
Mol.Cell, 2026

PubMed Abstract: The evolutionary arms race between bacteria and phages has driven the diversification of prokaryotic antiviral defense mechanisms, with nucleic acid degradation emerging as a central strategy. Here, we investigate a Higher Eukaryotes and Prokaryotes Nucleotide-binding (HEPN) domain-containing defense system from Escherichia coli that mediates RNase-dependent abortive infection. In contrast to canonical immune systems, where oligomerization triggers signaling, this system adopts a dodecameric autoinhibited architecture, with RNase activity unleashed upon oligomer dissociation. This activation mechanism is reminiscent of the dispersal of dandelion seeds, and we therefore term this defense system "Dandelion." We further identify the phage single-stranded DNA-binding (SSB) protein as a trigger for the Dandelion system, and phylogenetic analysis of SSB proteins uncovers the specificity underlying phage resistance. Our findings reveal a counterintuitive paradigm in bacterial immunity-‌oligomer disassembly as an activation switch, which challenges the long-standing dogma that protein oligomerization activates immune signaling.

PubMed: 42349403
DOI: 10.1016/j.molcel.2026.06.008

Experimental method

ELECTRON MICROSCOPY (3.33 Å)