Viral parts: chemists convert virus into nanoscale tool. (This Week).

Unless they have a cold, most chemists give viruses little thought. That may change now that some researchers are decorating these microbes with a variety of molecules--making the germs into potential building blocks in electronic circuits and new materials, as well as tools in biomedical therapies.

In recent research, scientists used a virus with a diameter of 30 nanometers, an appropriate choice for eventually controlling the synthesis of materials on scales that have been difficult to master, says chemist M.G. Finn of the Scripps Research Institute in La Jolla, Calif. "We have to do some things to [the virus to] make it perform, but at least the starting point here is just the right size," says Finn.

In the Feb. 1 Angewandte Chemie International Edition, Finn, Scripps biologist John E. Johnson, and their colleagues report decorating a virus whose genetics and structure are well understood. Called cowpea mosaic virus, it attacks plants including many types of beans. The shell of each virus consists of a geometric tiling of 60 identical protein units.

First, the researchers found that the only sites where the natural virus reacts chemically are 60 sulfur-containing chemical groups--one buried within each of its shell-protein units, says Finn. Next, the team created a genetic mutant of the virus in which each unit also sported a sulfur-containing amino acid, cysteine, on its outside surface. Then, the researchers exposed the mutated virus to fluorescent-dye molecules that bonded to the new cysteines. The dye also attached, but less readily, to the buried reactive locations in the mutant virus' protein units.

In another test, the researchers exposed the mutant virus to phosphorus-containing gold clusters. Using a low-temperature version of electron microscopy, they confirmed that the clusters attached to the 60 external cysteine locations.

Finn and Johnson now aim to modify the cowpea mosaic virus by attaching metals and other molecules so it can serve as a building block for new types of materials. Or, with the reactive sites adorned with proteins or other biological molecules, the viruses might deliver drugs within the body or reveal basic interactions between molecules and cells, says Finn.

The work is "fabulous," comments Mark Young of Montana State University in Bozeman, who studies viruses for use in drug delivery and the synthesis of nanoscale materials. Says Young, "This really changes how people think about what a virus is and its utility."