Enhanced Specificity Mutations Perturb Allosteric Signaling in CRISPR-Cas9

CRISPR-Cas9 is a molecular tool with transformative genome editing capabilities. At the molecular level, an intricate allosteric signaling is critical for DNA cleavage, but its role in the specificity enhancement of the Cas9 endonuclease is poorly understood. Here, solution NMR is combined with multi-microsecond molecular dynamics and graph theory-derived models to probe the allosteric role of key enhancement specificity mutations. We show that the mutations responsible for increasing the specificity of Cas9 alter the allosteric structure of the catalytic HNH domain, impacting the signal transmission from the DNA recognition region to the catalytic sites for cleavage. Specifically, the K855A mutation strongly disrupts the HNH domain allosteric structure, exerting the highest perturbation on the signaling transfer, while K810A and K848A result in more moderate effects on the allosteric intercommunication. This differential perturbation of the allosteric signaling reflects the different capabilities of the single mutants to increase Cas9 specificity, with the mutation achieving the highest specificity also strongly perturbing the signaling transfer. These outcomes reveal that the allosteric regulation is critical for the specificity enhancement of the Cas9 enzyme, and are valuable to harness the signaling network to improve the system’s specificity.