Researchers Decipher Protective Shield

The stunning image could help scientists find better ways to both fight viral infections and design new gene therapies.

It reveals the structure of a type of protein coat shared by hundreds of known viruses containing double-stranded RNA genomes. The image was painstakingly created from hundreds of high-energy X-ray diffraction images and paints the clearest picture yet of the viruses' genome-encasing shell called a "capsid."

"When these viruses invade cells, the capsids get taken inside and never completely break apart," said lead researcher Jane Tao, assistant professor of biochemistry and cell biology at Rice.

Capsids come into play because viruses can reproduce themselves only by invading a host cell and highjacking its biochemical machinery. But when they invade, viruses need to seal off their genetic payload to prevent it from being destroyed by the cell's protective mechanisms.

Though there are more than 5,000 known viruses, including whole families that are marked by wide variations in genetic payload and other characteristics, most of them use either a helical or a spherical capsid.

In their attempt to map precisely the spherical variety, Tao and lead author Junhua Pan, a postdoctoral fellow at Rice, first had to create a crystalline form of the capsid that could be X-rayed. They chose the oft-studied Penicillium stoloniferum virus F, or PsV-F.

"Because many viruses use this type of capsid, understanding how it forms could lead to new approaches for antiviral therapies," Tao said. "It could also aid researchers who are trying to create designer viruses and other tools that can deliver therapeutic genes into cells."

The research team used X-ray crystallography to decipher the structure of the capsid. Pan first spent several months creating hundreds of crystal samples of PsV-F. He then collected hundreds of high-intensity, high-energy X-ray diffraction images at the Cornell High Energy Synchotron Source, or CHESS, in Ithaca, N.Y. By analyzing the way the X-rays scattered when they struck the crystals, Pan and the team created a precise three-dimensional image of the spherical capsid.; Source: Rice University