New CRISPR Enzyme Mutation Is Nearly 100 Times More Precise

CRISPR gene-editing is based on a bacterial defense system that uses a specific enzyme to cut sections of a pathogen's DNA out of the picture, and stores it for future reference. If or when the pathogen is encountered again, the system can identify it, and also knows how to fight it.

Co-opting bacterial defense to cut DNA

Scientists co-opted this bacterial defense system as a working genetic engineering tool — employing the mechanism for CRISPR-Cas9, to search the target pathogen for a specific sequence of DNA — one that could cause disease — and then snip it out of the genetic code. Sometimes, this is followed by replacing it with a sequence more beneficial to the organic host, or human.

But to do this, the system uses a guide RNA that binds with the target sequence, triggering the Cas9 enzyme to make its cut. This is where precision comes into play, because, typically, things can go wrong here. Earlier studies have shown how the guide RNA sometimes binds to the wrong site, especially when the sequence resembles the right one. Additionally, editing the wrong DNA might potentially cause several other problems.

Enhancing the CRISPR enzyme

Wenzhou Medical University in China led the new study, where scientists investigated the possibility of more precise versions of the enzyme. They did so via the generation of varying mutations of Cas9, and then testing how well they could single identify a target sequence among other, very similar — but wrong — sequences.

And it worked. One specific mutation filtered out mismatches that were distinct from the desired target, down to a difference of one base pair. The team said the mistake makes it up to 93 times more precise than the original enzyme.

Tricks of the enzyme domain

Additionally, the scientists also learned why the improvement happened. In short, the new mutation affects the recognition domain of the enzyme, which weakened the contact between the guide RNA and Cas9. This means only much stronger pairings may trigger a cut — which means only the correct sequence can guarantee the snip will happen.

"Avoidance of off-target cleavage is a crucial challenge for development of CRISPR for medical interventions, such as correcting genetic diseases or targeting cancer cells," said Lead Researcher of the study Feng Gu, reports New Atlas. "Our results point the way to developing potentially safer gene therapy strategies."

Wherever CRISPR has gained new potential uses in medical fields, the question of safe use has followed. But knowing of a new CRISPR-Cas9 mutation rated at nearly 100 times more effective could help to assuage public concerns regarding the gene-editing tool.