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Mode of Action (MoA)
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hypothesised to act as a DNA mimic, with some tentative evidence that it binds Cas3.
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Evidence
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AcrIB2 was identified as an inhibitor of the type I-B CRISPR-Cas system through conjugation assays in Clostridioides difficile. A plasmid containing a protospacer targeted by the CRISPR system failed to establish in recipient cells unless AcrIB2 was expressed, indicating interference inhibition. In a self-targeting assay, induction of a CRISPR array targeting the chromosomal hfq gene was lethal unless AcrIB2 was co-expressed, resulting in restored cell viability and growth. Genomic sequencing after CRISPR induction showed loss of DNA coverage near the target site in the absence of AcrIB2, while co-expression of AcrIB2 preserved genomic integrity, confirming interference suppression. Deletion analysis of CRISPR-Cas operons demonstrated that only the partial cas operon is responsible for interference and is the target of AcrIB2. Expression of AcrIB2 in a strain lysogenized with φCD38-2 partially suppressed CRISPR-mediated toxicity, indicating its activity in a prophage context. Mass spectrometry following co-purification with tagged AcrIB2 revealed enrichment of Cas3, suggesting a direct interaction. Structural predictions and conserved sequence features supported a DNA mimicry mechanism of action.
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MoA Category
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unknown
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Subtype(s) of the defence system(s) inhibited by the protein
Defence Subtype
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Clostridioides difficile type I-B CRISPR-Cas
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Relevant publication(s)
DOI
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10.1128/msphere.00401-23
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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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-
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Genome(s) encoding the protein
Protein Source
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Clostridium difficile phage φCD38-2
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Defence system(s) inhibited by the protein
Defences
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CRISPR-Cas
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