CRISPR/CAS9 has emerged as a flexible and effective approach for genome editing with a promise for the correction of disease-causing mutations. However, most studies have so far demonstrated CRISPR as an on/off system, with little temporal control of its activity or function. Now, new research from the University of Toronto described the discover of a number of proteins that allow to precisely do this: control the activity of CRISPR specifically and conditionally, and at defined time points.
Published in Cell, the study is titled “Naturally Occurring Off-Switches for CRISPR-Cas9” from the lab of Dr. Alan Davidson.
The authors identified naturally occurring protein inhibitors of a CRISPR-Cas9 system. A bioinformatics-based approach allowed the authors to discover three proteins that inhibit N. meningitidis type II-C CRISPR-Cas system, by interacting with NmeCas9 to function as off-switches for NmeCas9 genome editing activity.
They further showed that members of all three anti-CRISPR families bind directly to the NmeCas9/sgRNA complex and inhibit in vitro DNA cleavage. Interestingly, they displayed unrelated sequences, leading the authors to postulate that they operate under different mechanisms as well.
Evolutionarily, Cas9-associating anti-CRISPRs were postulated to prevent the acquisition of new spacers (such as viral DNA) in response to external invasions, with CRISPR having a profound effect on horizontal gene transfer. This implication has profound effects on therapeutics being developed based on CRISPR/CAS9 technology.
Therapeutically, these proteins can prevent off-target effects and are thus exciting potential therapeutic targets.