Image of Viral Coat

Posted on March 23, 2009  Comments (0)

image of exterior of virus - made up of 5 million atomsHigh-energy X-ray diffraction was used to pinpoint some 5 million atoms in the protective protein coat of the PsV-F virus. The coat’s symmetrical features are shared by hundreds of viruses. The red and yellow sections illustrate how building blocks of four proteins come together to form the spherical shell.

The image 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.”

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.

“Spherical viruses like this have symmetry like a soccer ball or geodesic dome,” Pan said. “The whole capsid contains exactly 120 copies of a single protein.” Previous studies had shown that spherical capsids contain dozens of copies of the capsid protein, or CP, in an interlocking arrangement. The new research identified the sphere’s basic building block, a four-piece arrangement of CP molecules called a tetramer, which could also be building blocks for other viruses’ protein coats.

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