A small loop in an anti-CRISPR protein revealed how it inhibits a particular Cas9 enzyme more strongly than a related protein. Transferring the loop improved the weaker inhibitor in a single peer-reviewed molecular study. The experiments connect protein structure with guide-RNA positioning, offering a basis for engineering inhibitors without establishing a safe treatment in people.
An extended loop in an anti-CRISPR protein helped strengthen inhibition of a particular Cas9 enzyme. Cas9 cleaves DNA in bacterial defence and is also used in gene-editing tools. Shen Wang and colleagues compared two related inhibitors in a single peer-reviewed study published on October 16. The protein AcrIIC1Boe showed stronger inhibition than AcrIIC1Nme1 in biochemical tests.[1]
Both proteins bound the enzyme’s HNH region, which participates in DNA cleavage. Their similar core binding arrangements left the difference in potency unexplained. Structural measurements and molecular simulations instead pointed to the extended loop beside the region accommodating guide RNA. This RNA directs Cas9 to its DNA target. The loop interfered with its positioning and with progression of RNA–DNA pairing, adding to the inhibition associated with covering the catalytic site.[1]
Removing the functional loop largely eliminated strong inhibition. Transplanting it into the weaker protein increased inhibitory activity, supporting a link between structure and function. The effect depends on the molecular surroundings of the selected Cas9 system and does not establish that all anti-CRISPR proteins work this way. The experiments provide a basis for engineering this protein family. They do not establish therapeutic effectiveness, delivery through the body or the safety of human genome editing.[1]
