Immune System Enzymes Sense Viral RNA

Experts from Penn State and the University of Connecticut, in the US, and the University of Beijing, in China, have recently discovered the fact that a certain enzyme inside the human immune system is able to detect certain pairs of viral RNA belonging to infecting pathogens. The enzyme, known as protein kinase R (PKR), is regulated differently by common RNA inside the body and the RNA in pathogens, and its changes provide a basis for biologists to assess what kind of infection it might be.

“PKR plays an important role in the human immune system. It is activated by long stretches of double-stranded RNA. As a part of our built-in immune response, PKR can recognize viral double-stranded RNAs and inhibit their production,” the first author of the new study, chemistry graduate student Laurie Heinicke, from the Pennsylvania State University (Penn State), explains. “Once activated by certain RNAs, PKR stops protein synthesis in the infected cell and ultimately causes cell death,” she adds, quoted by e! Science News.

When infecting a host, viruses are in the nasty habit of injecting their own genetic material inside cells, forcing them to essentially produce more generations of viruses, rather than their usual chemicals. In order for this to happen, viral RNA is released inside the cell. If PKR detects it, it binds to specific locations on its surface, and renders it useless. “We showed that a small region of the HIV-1 genome termed TAR can regulate PKR. The caveat, however, is that this RNA must form a dimer [or linked pair] in order to be an activator,” the expert adds.

“The length needed for one PKR to bind to RNA is fifteen base pairs. To get two PKRs to bind and dimerize, you need an RNA strand that is twice as long,” Penn State Professor of Chemistry Philip Bevilacqua, who has also worked on the project with colleague James Cole, an associate professor at the University of Connecticut, shares. Details of the new work appear in the latest issue of the Journal of Molecular Biology.

Creating RNA molecules that remove TAR defects “helps us find what the actual molecular structure is that activates PKR. It is still basic research for now, but finding the cause for this may ultimately lead to understanding disease,” Bevilacqua concludes.