identifier: traitmech:000231 label: Kiwa system definition: A phage defense system in which an organism possesses a two-component Kiwa locus encoding the transmembrane sensor KwaA and DNA-binding effector KwaB that assemble into a membrane-associated supercomplex and coordinate phage-attachment sensing with inhibition of phage DNA replication and late transcription. definition_source: DOI:10.1016/j.cell.2025.07.002 trait_category: GENOMICS term_kind: CLASS mapping_status: PROPOSED parent_traits: - traitmech:000209 synonyms: - synonym_text: Kiwa synonym_type: EXACT_SYNONYM source: DOI:10.1016/j.cell.2025.07.002 evidence: - reference: DOI:10.1126/science.aar4120 snippet: Kiwa KwaAB pfam16162 No annotated domain 934 924 (1.8%) Membrane associated notes: Doron et al. reported Kiwa/KwaAB as a membrane-associated defense system in their pangenome-scale antiphage-system discovery screen. - reference: DOI:10.1016/j.cell.2025.07.002 snippet: Kiwa, a widespread two-component system composed of the transmembrane sensor KwaA and the DNA-binding effector KwaB notes: Zhang et al. support defining Kiwa as a recurring two-component KwaA/KwaB antiviral system. - reference: DOI:10.1016/j.cell.2025.07.002 snippet: KwaA and KwaB assemble into a large, membrane-associated supercomplex notes: Zhang et al. connect the KwaA and KwaB components to membrane-associated supercomplex assembly. - reference: DOI:10.1016/j.cell.2025.07.002 snippet: Upon phage binding, KwaA senses infection at the membrane, leading to KwaB binding of ejected phage DNA and inhibition of replication and late transcription, without inducing host cell death notes: Zhang et al. connect phage binding to KwaA-dependent membrane sensing, KwaB binding of phage DNA, and inhibition of phage replication and late transcription. - reference: DOI:10.1016/j.cell.2025.07.002 snippet: its antiviral activity requires association with KwaA, suggesting spatial or conformational regulation notes: Zhang et al. support KwaA-KwaB association as required for Kiwa antiviral activity. - reference: DOI:10.1016/j.cell.2025.07.002 snippet: Kiwa coordinates membrane-associated detection of phage infection with downstream DNA binding by its effector, forming a spatially coordinated antiviral mechanism notes: Zhang et al. summarize the Kiwa system-level mechanism as membrane-associated phage-infection detection coordinated with effector DNA binding. canonical_examples: - taxon_id: NCBITaxon:562 taxon_label: Escherichia coli note: Zhang et al. characterized the Escherichia coli O55:H7 Kiwa system and showed that its KwaA/KwaB pair assembles into a membrane-associated supercomplex that inhibits phage DNA replication and late transcription. reference: DOI:10.1016/j.cell.2025.07.002 causal_graphs: - graph_id: kiwa_membrane_sensing_dna_binding title: Kiwa coordinates membrane sensing with phage DNA binding description: Evidence-backed process sketch linking a Kiwa kwaAB locus to KwaA-KwaB supercomplex assembly, membrane-associated phage-infection sensing, binding of ejected phage DNA, and inhibition of phage DNA replication and late transcription. scope_status: NONMECHANISTIC scope_notes: The graph captures the characterized two-component Kiwa mechanism without asserting one exact phage receptor, the precise KwaA conformational change, the structural basis of KwaB DNA binding, Gam-mediated counter-defense, or RecBCD rescue as universal across all Kiwa loci. nodes: - node_id: kiwa_locus label: Kiwa locus node_type: GENETIC_ELEMENT description: A two-component phage-defense locus encoding the transmembrane sensor KwaA and DNA-binding effector KwaB. - node_id: kwaab_supercomplex_assembly label: KwaA-KwaB supercomplex assembly node_type: BIOLOGICAL_PROCESS description: Assembly of KwaA and KwaB into a large membrane-associated Kiwa supercomplex. - node_id: membrane_phage_sensing_and_dna_binding label: membrane phage sensing and DNA binding node_type: BIOLOGICAL_PROCESS description: KwaA-mediated membrane sensing of phage binding coordinated with KwaB binding to ejected phage DNA. - node_id: phage_replication_and_late_transcription label: phage replication and late transcription node_type: BIOLOGICAL_PROCESS description: Phage DNA replication and late phage transcription inside an infected bacterial host. - node_id: kiwa_system_trait label: Kiwa system node_type: TRAIT grounding: traitmech:000231 description: Possession of a genome-encoded Kiwa phage-defense system. - node_id: phage_defense_system label: phage defense system node_type: TRAIT grounding: traitmech:000209 description: Possession of one or more genome-encoded immune systems that inhibit bacteriophage infection. edges: - subject: kiwa_locus predicate: contributes to predicate_id: RO:0002326 object: kwaab_supercomplex_assembly description: The Kiwa kwaAB locus encodes KwaA and KwaB components that assemble into a membrane-associated supercomplex. evidence: - reference: DOI:10.1016/j.cell.2025.07.002 snippet: KwaA and KwaB assemble into a large, membrane-associated supercomplex notes: Zhang et al. support KwaA/KwaB supercomplex assembly. - subject: kwaab_supercomplex_assembly predicate: enables predicate_id: RO:0002327 object: membrane_phage_sensing_and_dna_binding description: Association with KwaA is required for Kiwa antiviral activity despite independent KwaB DNA binding. evidence: - reference: DOI:10.1016/j.cell.2025.07.002 snippet: its antiviral activity requires association with KwaA, suggesting spatial or conformational regulation notes: Zhang et al. support KwaA association as required for KwaB antiviral activity. - subject: membrane_phage_sensing_and_dna_binding predicate: mitigates predicate_id: METPO:2007407 object: phage_replication_and_late_transcription description: KwaA sensing of phage binding coordinates with KwaB binding of ejected phage DNA to inhibit phage replication and late transcription. evidence: - reference: DOI:10.1016/j.cell.2025.07.002 snippet: Upon phage binding, KwaA senses infection at the membrane, leading to KwaB binding of ejected phage DNA and inhibition of replication and late transcription notes: Zhang et al. connect Kiwa membrane sensing and KwaB DNA binding to inhibition of phage replication and late transcription. - subject: membrane_phage_sensing_and_dna_binding predicate: confers predicate_id: METPO:2007700 object: kiwa_system_trait description: Spatially coordinated membrane-associated phage sensing and effector DNA binding realizes the Kiwa antiphage-defense phenotype. evidence: - reference: DOI:10.1016/j.cell.2025.07.002 snippet: Kiwa coordinates membrane-associated detection of phage infection with downstream DNA binding by its effector notes: Zhang et al. summarize the system-level Kiwa antiviral mechanism. - subject: kiwa_system_trait predicate: is a predicate_id: rdfs:subClassOf object: phage_defense_system description: Kiwa system possession is a phage-defense-system trait. evidence: - reference: DOI:10.1016/j.cell.2025.07.002 snippet: Our findings support a model in which Kiwa coordinates membrane-associated detection of phage infection notes: Zhang et al. support Kiwa as an antiviral phage-defense system. discussions: - discussion_id: kiwa-activation-and-counterdefense-gap prompt: Resolve Kiwa activation, phage counter-defense, and RecBCD-rescue details before minting narrower Kiwa mechanism children. kind: KNOWLEDGE_GAP status: OPEN rationale: Zhang et al. support a KwaA/KwaB membrane-associated antiviral supercomplex and also describe the phage Gam DNA-mimic counter-defense and RecBCD-dependent restoration of Kiwa protection, but the first TraitRecord stays at the system level until separate review resolves the activation conformational change, exact DNA-binding state, phage counter-defense breadth, and RecBCD connection. posed_by: codex posed_date: '2026-09-15' curation_history: - timestamp: '2026-09-15T22:47:00Z' curator: codex action: MINTED_TRAITMECH_ID changes: Minted Kiwa system as a DOI-backed GENOMICS TraitRecord under the phage defense system parent after an ignored-and-hidden duplicate review found no exact live TraitMech, METPO, or prior proposal record; the replacement placeholder is reserved in proposals/metpo_traitmech_v108. llm_assisted: true