Using a high-resolution imaging technique called cryo-EM, the team discovered that when this protein, named Cas12a2, binds to a specific sequence of genetic material from a potentially dangerous virus, called a target RNA, the side of Cas12a2 swings out to reveal an active site, similar to a spring-loaded shooter . The active site then begins to indiscriminately cut any genetic material it comes into contact with. The researchers found that with a single mutation in the Cas12a2 protein, the active site degrades only single-stranded DNA—a feature particularly useful in developing new diagnostics tailored for any of a wide variety of viruses.
A test based on this technology could theoretically combine the best features of PCR-based tests that detect genetic material from the virus (high sensitivity, high accuracy, and the ability to detect active infection) with the best features of rapid home diagnostic tests. (cheap production without the need for specialized laboratory equipment). It would also be easily adaptable to any new RNA virus.
David Taylor, associate professor of molecular biosciences says “If some new virus comes out tomorrow, all you have to do is figure out its genome and then change the guide RNA in your test and you’ll have a test against it,” said.
Such a diagnosis would still require separate work and would likely involve taking a saliva or nasal sample from a patient that would be mixed with the team’s modified Cas12a2 protein, a piece of guide RNA that acts as a mugshot to identify a particular virus, and a fluorescent probe. designed to light up when its single-stranded DNA is cut. CRISPR is the name for a set of tools that occur naturally in bacteria but that scientists have modified for use in gene editing. It is the first CRISPR protein found to degrade such a wide range of genetic material.
Jack Bravo, a postdoctoral fellow at UT Austin and co-first author of the paper says “Cas12a2 basically grabs the two ends of the DNA double helix and bends it really tight so the helix in the middle opens up, and then that allows this active site to destroy pieces of DNA that become single-stranded. That’s what makes Cas12a2 different from all the other DNA-targeting systems.”
Taylor, Bravo, Hallmark and Jackson are inventors on a patent application involving modifications to the Cas12a2 protein that allow it to cleave only single-stranded DNA and for use in diagnostics. UT Austin’s Office of Technology Commercialization manages intellectual property and seeks to find industry partners who can help realize the technology’s potential.
This work was supported in part by the National Institute of General Medical Sciences of the National Institutes of Health, the German Federal Agency for Breakthrough Innovation, the Welch Foundation, and the Robert J. Kleberg, Jr. Foundation. and Helen C. Kleberg. David Taylor is a CPRIT Fellow supported by the Cancer Prevention and Research Institute of Texas.
