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Mode of Action (MoA)
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binds to the crRNA-exposed face of Cas13a, preventing access to the target RNA and the conformational changes required for nuclease activation.
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Evidence
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Phage fLS46 carrying the acrVIA1 gene overcame Cas13a-mediated immunity, while deletion of acrVIA1 (ΔacrVIA1) rendered the phage susceptible to CRISPR targeting. Infection assays with L. seeligeri strains harboring Cas13a-targeting spacers demonstrated that ΔacrVIA1 mutants were cleared, whereas wild-type fLS46 replicated efficiently even under conditions of multiple spacer targeting and extremely low multiplicity of infection. Conjugation assays revealed that plasmid transfer was inhibited by Cas13a unless AcrVIA1 was expressed, confirming its ability to suppress defense. In vitro assays showed that AcrVIA1 binds to the Cas13a–crRNA complex, blocking both cis- and trans-RNase activities. Electrophoretic mobility shift assays (EMSA, ECO_0001807) confirmed that AcrVIA1 prevents target RNA binding. Co-immunoprecipitation (ECO_0000085) and cryo-EM (ECO_0006181) revealed that AcrVIA1 interacts with both crRNA and multiple Cas13a domains, stabilizing crRNA in a conformation incompatible with activation.
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MoA Category
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binds and inhibits host defence system
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Subtype(s) of the defence system(s) inhibited by the protein
Defence Subtype
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Listeria seeligeri type VI-A CRISPR-Cas
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Relevant publication(s)
DOI
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10.1126/science.abb6151
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Other components of the anti-defence system
Multicomponent System
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-
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Known structure in PDB
PDB ID
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6VRB_C
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Genome(s) encoding the protein
Protein Source
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Listeriaphage (fLS46)
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Defence system(s) inhibited by the protein
Defences
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CRISPR-Cas
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