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Kiwa is a membrane-embedded defense supercomplex activated at phage attachment sites
Zhiying Zhang1, Thomas C Todeschini2, Yi Wu2
1Structural Biology Program, Memorial Sloan Kettering Cancer Center, New York, NY, USA; Interdisciplinary Life Sciences Graduate Programs, Austin, TX 78712, USA; Center for Systems and Synthetic Biology, University of Texas at Austin, Austin, TX 78712, USA.
Cell
|July 29, 2025
Summary
Researchers discovered Kiwa, a bacterial antiviral defense system. This two-component system, KwaA and KwaB, detects phage infection at the membrane and binds phage DNA to halt replication, protecting the cell without causing death.
Area of Science:
- Microbiology
- Molecular Biology
- Structural Biology
Background:
- Bacteria and archaea possess numerous, often uncharacterized, antiviral defense mechanisms.
- Understanding these systems is crucial for deciphering microbial immunity and developing novel biotechnological tools.
Purpose of the Study:
- To characterize the Kiwa system, a widespread two-component antiviral defense mechanism in prokaryotes.
- To elucidate the molecular mechanism of Kiwa-mediated phage defense.
Main Methods:
- Cryogenic electron microscopy (cryo-EM) to determine the structure of the Kiwa complex.
- Biochemical assays to analyze DNA binding and protein interactions.
- Genetic manipulation to study the role of phage proteins in inhibiting Kiwa.
Main Results:
- Cryo-EM revealed KwaA and KwaB form a large, membrane-associated supercomplex.
- Kiwa detects phage infection via KwaA at the membrane, leading to KwaB binding of phage DNA.
- This process inhibits phage DNA replication and transcription without host cell lysis.
- Phage protein Gam inhibits KwaB, but RecBCD system co-expression restores Kiwa function.
Conclusions:
- Kiwa functions as a spatially coordinated antiviral system, linking membrane-based infection detection to effector-mediated DNA binding.
- The system's activity is regulated by protein-protein interactions and potentially modulated by phage-encoded factors.
- Kiwa represents a significant addition to the known repertoire of prokaryotic antiviral strategies.
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