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Mode of Action (MoA)
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binds to the Cas5f-8f tail and Cas7.6f subunits of the Csy complex to block target DNA recognition.
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Evidence
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AcrIF13 from Moraxella catarrhalis was ectopically expressed in P. aeruginosa (ECO_0000017), completely inhibiting type I-F CRISPR-Cas immunity and restoring phage replication. Competitive binding experiments demonstrated that AcrIF13 targets the Cas5f-Cas8f tail of the complex, similarly to AcrIF2, and also requires Cas7.6f for stable binding. Native gel electrophoresis confirmed that AcrIF13 does not bind the Cas5f-8f heterodimer alone, unlike other Acrs, indicating multivalent interactions. Electrophoretic mobility shift assays (EMSA, ECO_0000096) showed that AcrIF13 potently blocked DNA binding to the Csy complex at a 1:1 molar ratio, confirming its role as a DNA mimic. Site-directed mutagenesis of acidic residues on AcrIF13 and basic residues on Cas8f and Cas7f reduced binding affinities by up to 40-fold (e.g., D113K mutant KD = 67.65 nM), further confirming critical electrostatic interactions mediating inhibition.
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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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Pseudomonas aeruginosa type I-F CRISPR-Cas
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Relevant publication(s)
DOI
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10.1126/science.aau5174,
10.1016/j.jbc.2022.101636
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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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7FI4
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Genome(s) encoding the protein
Protein Source
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Moraxella phage Mcat5
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Defence system(s) inhibited by the protein
Defences
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CRISPR-Cas
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