Researchers Discover Genetic Scissors That Turn Off With Built-in Timer

The CRISPR genetic scissors, a new molecular biology tool, originated in an ancient bacterial immune system. But once the viral attack is defeated, the cell must recover.

Researchers from the University Hospital Bonn (UKB) and the University of Bonn, in collaboration with researchers from the Pasteur Institute in France, have discovered a timer built into genetic scissors that allows them to turn off automatically. The results of the study were published in the journal Nucleic Acid Research.

Some bacteria have developed CRISPR genetic scissors in response to attacks by so-called phages. This bacterial immune system recognizes the phage’s genetic material, destroys it and thus protects against viral attacks.

Upon detection of phages, type III variants of these immune systems produce messenger substances containing cyclic oligoadenylates (cOA), with which the bacteria trigger a complex emergency plan. This makes it possible to optimally combat a virus on a broad front.

The research team, led by Dr. Gregor Hagelueken from the Institute of Structural Biology at UKB, which is a member of the Transdisciplinary Research Area (TRA) Life and Health and the ImmunoSensation2 Cluster of Excellence at the University of Bonn, discovered that the messenger substance cA₄ The protein produced by the gene scissors binds to a protein called CalpL. The protein scissors thus activated trigger a signaling cascade that helps the cell survive the viral attack.

The Bonn researchers have thus discovered a completely new aspect of CRISPR systems, which can be easily reprogrammed for biotechnological and medical purposes. “These CRISPR-activated protein scissors that we have discovered are a completely new tool in the toolbox of molecular biology,” says Niels Schneberger, a doctoral student at the Institute of Structural Biology at the University of Bonn’s UKB, who played a key role in the discovery of the CalpL protein.

Cellular recovery by limiting the antiviral response

“After a viral attack, however, it is crucial to remove the remaining cyclic oligoadenylates in order to terminate the antiviral reaction and return the cell to its normal state,” says Sophie Binder, who shares first authorship of the study with Schneberger and is also a doctoral student at the Institute of Structural Biology at the University of Bonn at UKB.

In cooperation with researchers from the Institut Pasteur in Paris and the Kekulé Institute of Organic Chemistry and Biochemistry at the University of Bonn, the Bonn researchers have now been able to show that the SAVED domain of the protease CalpL has a ring nuclease activity that cleaves cA₄.

“The protein therefore contains a kind of molecular timer that deactivates the immune response. By breaking down the cA₄ “In linear fragments, the duration of the immune response is regulated, allowing a controlled return of the cell to normal conditions,” explains Binder.

A switchable protease like CalpL is also of great interest for biotechnological applications. For example, it could be used as a molecular sensor. “The recently discovered ring nuclease activity is actually a disadvantage for such purposes,” says Dr. Hagelueken, PD. “However, in our study we were also able to show how the ring nuclease activity can be inhibited in a targeted manner so that the sensor does not deactivate.”