With no approved vaccine and limited treatment for RSV, doctors prescribe the antiviral drug ribavirin only in the most severe cases because it is expensive and not very effective. Thus, most people with RSV receive only supportive care to make them more comfortable while their bodies fight off the virus. People with weakened immune systems face a tough fight with RSV. The researchers say that solving the structure of this elusive protein will enable them to see what the protein looks like and help them define what it does and how it does it. Ultimately, this capability and finding could lead to new targets for vaccine or drug development.
Scientists have long known that a nonstructural RSV protein (known as NS1) is key to the virus’s ability to evade the body’s immune response. However, its structure was unknown, so scientists were unable to determine exactly how the enigmatic NS1 interfered with the immune system. Using X-ray crystallography, the scientists determined the three-dimensional (3D) structure of NS1, and, in a detailed analysis of the structure, they identified a piece of the protein known as the alpha 3 helix, possibly critical for suppressing the immune response.
The researchers created different versions of this NS1 protein, with some having an intact and some with a mutated alpha 3 helix region. They tested the functional impact of helix 3 and created a set of viruses containing either the original or the mutant NS1 genes, measuring the effect on the immune response when they infected cells with these viruses. They found that viruses with the mutated helix region did not suppress the immune response, while the ones with the intact helix region did, globally modulating the immune response.
The findings also showed that the protein’s alpha 3 helix region was necessary for the virus to dial down the body’s immune response, giving the virus a better chance of surviving and multiplying—in other words, causing disease. Thus, a vaccine or treatment that targets the alpha 3 helix may supply what is needed to prevent immune suppression.
Chatterjee, S., et al. “Structural Basis for Human Respiratory Syncytial Virus NS1-Mediated Modulation of Host Responses.” Nat. Microbiol. 2, Article 17101 (2017). [DOI:10.1038/nmicrobiol.2017.101].
Instruments and Facilities Used: X-ray crystallography at the Advanced Photon Source at Argonne National Laboratory.