Researchers at the Francis Crick Institute have used cutting-edge imaging techniques to gain new insights into how cells detect and defend themselves against viruses. The study, published in Nature, reveals a detailed molecular map of how the protein complex, known as the cGAS-STING pathway, assembles and activates to trigger an immune response. This work provides a better understanding of cellular defence mechanisms and potential targets for antiviral therapies.

Viruses are intracellular parasites that rely on host cells to replicate and survive. To combat viral infections, cells have evolved various defence mechanisms, including the cGAS-STING pathway. This pathway plays a crucial role in sensing DNA released from invading viruses and activating the immune system to clear the infection.

The cGAS-STING pathway is initiated when the protein cGAS binds to double-stranded DNA (dsDNA). Upon DNA binding, cGAS undergoes a conformational change and synthesises a signalling molecule called cyclic GMP-AMP (cGAMP). cGAMP then binds to and activates the STING protein, leading to the production of immune molecules that help eliminate the virus.

Using high-resolution imaging techniques, the researchers were able to visualise the assembly and activation of the cGAS-STING pathway at unprecedented detail. They observed how cGAS changes its structure upon dsDNA binding and forms filaments that extend and connect with other cGAS molecules. These filaments then interact with STING, triggering its activation.

The study also revealed the molecular mechanisms by which the cGAS-STING pathway is regulated. They found that a protein called USP18 can remove the cGAMP molecule from STING, effectively turning off the pathway and preventing excessive inflammation. This negative regulation ensures a balanced immune response to viral infections.

Understanding the molecular details of the cGAS-STING pathway is crucial for developing new antiviral therapies. By targeting specific steps in this pathway, scientists may be able to enhance the immune system's ability to detect and eliminate viruses, leading to more effective treatments for viral infections.