Viral Map

In their frustratingly slow effort to conquer the common cold, medical scientists decades ago learned that the world's most prevalent disorder is usually caused by any of a hundred or so different kinds of viruses. Under an electron microscope, they all look like simple fuzzy balls, but the precise architecture of these so-called rhinoviruses has remained obscure. Last week teams of scientists from Purdue and the University of Wisconsin, Madison, reported in the journal Nature that they had mapped in exquisite atomic detail the structure of a human cold virus called HRV14. Their achievement marked the first time that the shape of an animal virus had been so precisely determined, and raised hopes that a cure for the common cold might be possible after all.

HRV14 is marvelously complex; its genetic material is surrounded by a 20- sided outer shell that vaguely resembles a soccer ball. The sides consist of three identical triangles each containing three proteins on its irregular surface, and one below it. On the surface proteins, the researchers discovered, features that resemble mountaintops are actually antigens, structures that antibodies seek out and attach themselves to when attacking the virus. A "canyon" snakes between these mountaintops and is believed by scientists to be shaped specifically to fit over projections, or receptors, on the surface of human cells. The virus may use this canyon to attach itself to a receptor, like a keyhole receiving a key, before attacking the cell.

Armed with this knowledge of the viral topography, scientists, at least in theory, can begin closing in on a cure for the common cold. For example, a lab-made antibody designed to slide into the canyon and block it would prevent the virus from attaching to a cell. One problem with that approach, researchers say: antibodies are too large to enter the canyons. But another approach is possible, involving the key (the receptor) instead of the lock (the canyon). By developing a drug that somehow coats the receptors, scientists may prevent the virus from joining the cell.

In fathoming the shape of HRV14, the Purdue and Wisconsin teams depended heavily on high technology. Using X rays produced by Cornell University's High Energy Synchrotron Source, they passed a beam through crystallized samples of the virus. Data derived from the interactions between the X rays and the viral atomic structure were then fed into Purdue's Cyber 205 supercomputer, which enabled the researchers to produce a detailed three-dimensional picture of the virus. In fact, the supercomputer was the hero of the project. "The final set of calculations were made in a month," says Michael Rossmann, who headed the Purdue team. Without the Cyber, "they might have taken ten years."