SuperFi-Cas9: the future of gene editing technology?

Written by Harriet Stanwix

A team at the University of Texas at Austin (UT Austin; TX, USA) recently published research in the journal Nature, which resulted in safer use of CRISPR gene editing 

The main obstacle of using CRISPR gene editing on humans is that the molecular machinery can alter the wrong section of the host’s genome. When these errors occur, the machinery creates genetic mutations rather than repairing them. 

To address this issue, researchers from UT Austin redesigned a key component of the CRISPR gene editing tool – Cas9 – to behave in a more efficient and safe manner. While there have been previous attempts to redesign Cas9 to reduce off-target interactions, none have been able to retain the efficiency and speed that UT Austin’s team have achieved. 

Kenneth Johnson, Professor of Molecular Biosciences and co-author of the study, stated: “this really could be a game changer in terms of a wider application of the CRISPR Cas systems in gene editing”. The results were recently published in the journal Nature. 

The new version has been titled SuperFi-Cas9 and is 4000 times less likely to cut off-target sites. Jack Bravo, Postdoctoral Fellow and co-author of the study, reinforced that “[previous versions are] safer than the naturally occurring Cas9, but it comes at a big cost: they’re going extremely slowly. SuperFi-Cas9 is like a self-driving car that has been engineered to be extremely safe, but it can still go at full speed.” 

CRISPR gene editing tools have been modified from systems that naturally occur in bacteria. Cas9 protein floats around in the environment searching for DNA containing a specific sequence. On certain occasions, Cas9 will still target the DNA even if all the letters are not correct.   

Kinetics-guided structure determination – previously created by a research team at UT Austin – is a technique utilizing a cryo-electron microscope to record images of interactions between Cas9 and mismatched DNA. Utilizing the images, it was determined that Cas9 has a finger-like structure, which takes hold of the DNA, making it behave as if it were the correct sequence.   

Bravo explained further: “it’s like if you had a chair and one of the legs was snapped off and you just duct taped it together again. It could still function as a chair, but it might be a bit wobbly. It’s a pretty dirty fix.” 

The researchers from UT Austin utilized this discovery to redesign the extra finger on Cas9, so that instead of stabilizing mismatched DNA, the finger is driven away from the DNA. This halts Cas9, preventing the process of cutting and editing, which results in SuperFi-Cas9, and makes the procedure more efficient.  

The use of SuperFi-Cas9 was demonstrated in test tubes during this study. Research will continue and the team plan to test SuperFi-Cas9 in living cells and to develop safer and more active versions of Cas9. 

Source:

Bravo J, Liu M, Hibshman G et al. Structural basis for mismatch surveillance by CRISPR–Cas9. Nature https://doi.org/10.1038/s41586-022-04470-1 (2022) (Epub ahead of print).