Watching CRISPR-Cas9 in Action

In a study published today in Nature Strucutral and Molecular Biology, scientists have captured high-resolution, three-dimensional images of an enzyme in the process of precisely cutting DNA strands.

The images, which were captured using a technique called cryogenic electron microscopy (cryo-EM), reveal new information about how the gene-editing tool CRISPR-Cas9 works and may help researchers develop more efficient and precise versions of CRISPR-Cas9. The findings may help with the future treatment and prevention of a range of human diseases caused by DNA mutations, from cancer to cystic fibrosis and Huntington disease.

“It is exciting to be able to see at such a high level of detail how Cas9 actually works to cut and edit DNA strands,” says senior author Sriram Subramaniam from UBC. “These images provide us with invaluable information to improve the efficiency of the gene-editing process so that we can hopefully correct disease-causing DNA mutations more quickly and precisely in the future.”

To better understand the sequence of events involved in the process, Subramaniam and colleagues used cryo-EM technology to image the Cas9 enzyme at work. The images provide unprecedented glimpses of the stepwise molecular motions that occur in the course of DNA cutting by Cas9, including a snapshot of the cut DNA still attached to the enzyme immediately before release.

“One of the main hurdles preventing the development of better gene-editing tools using Cas9 is that we didn’t have any images of it actually cutting DNA,” says co–senior author Miljan Simonovic of the University of Illinois. “But now we have a much clearer picture, and we even see how the major domains of the enzyme move during reaction and this may be an important target for modification.”

The Subramaniam laboratory was the first to achieve atomic resolution imaging of proteins and protein-bound drug molecules using cryo-EM. In the last few years, they have pioneered the use of cryo-EM to visualize a variety of proteins including metabolic enzymes, brain receptors, and DNA-protein complexes.