A Broad-Spectrum Inhibitor of CRISPR-Cas9.
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AcrIIC1 is a broad-spectrum Cas9 inhibitor acting at the cleavage step
"AcrIIC1 is a broad-spectrum Cas9 inhibitor that prevents DNA cutting by multiple"
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Inhibition occurs without preventing DNA binding, which is the diagnostic that separates this mechanism from the DNA mimics
"The ability of AcrIIC1 to inhibit multiple Cas9 orthologs without preventing DNA binding suggested that it targets a conserved region of Cas9 involved in DNA cleavage."
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Domain-swap chimeras between a binding and a non-binding Cas9 orthologue localise the interaction to the HNH domain
"These results indicated that the HNH domain is the primary site of interaction for AcrIIC1."
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The contact is at the HNH active-site interface, via ionic and hydrogen-bonding interactions
"AcrIIC1 binds to the active site interface of the HNH domain through several ionic and hydrogen-bonding interactions."
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The outcome is a Cas9 trapped on its target in a catalytically inactive state
"These results suggested that AcrIIC1 traps Cas9 in its DNA-bound state, while inhibiting DNA cleavage."
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Breadth across orthologues follows from binding the most conserved domain of Cas9
"The ability of AcrIIC1 to bind to the most conserved domain of Cas9 explains its ability to robustly inhibit related Cas9 orthologs"
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AcrIIA4 is contrasted in the same paper as a DNA mimetic that prevents DNA binding, confirming that the two mechanism classes are distinguished in the primary literature
"Both of these mechanisms are different from that of the anti-CRISPR protein AcrIIA4, which acts as a DNA mimetic that prevents DNA binding by occupying t"