Polio invader caught on camera

January 28, 2000

Like a closed-circuit television picture of burglars breaking into a home, scientists have caught a polio virus in the process of entering a host cell for the first time.

The three-dimensional images reveal the remarkable way in which the virus is able to spread inside the body and begin to wreak havoc.

Although vaccination programmes have eradicated polio from the West and are poised to do the same in the developing world, little is known about how the virus invades the cells of the intestines and progresses into the nervous system.

James Hogle and colleagues at the Harvard Medical School and the National Institutes of Health in the United States used a combination of cryoelectron microscopy and X-ray crystallography to capture images of the virus as it begins its assault. It is thought many other disease-causing viruses may act in a similar fashion.

"Understanding these viruses gives you a route to potentially making drugs to thwart them," said Dr Hogle, professor of biological chemistry and molecular pharmacology.

The structural details, to be published in the forthcoming issue of the Journal of Virology, illustrate an astonishing sophistication of the most simple form of life yet discovered.

From the moment the polio virus attaches itself to its host - a healthy cell in the intestine - it starts a series of chemical transformations to evade the body's defences.

It makes tiny adjustments to the protein shell that protects its genetic material so that it can tighten its grip on one of the cell's receptors. Temporary openings are then created in the shell through which tiny protein threads are thrown out, embedding themselves in the host cell membrane like boarding ropes thrown onto a ship by pirates.

Not only do these threads bind the virus tighter still to the shell but they might also create pores for the virus's genetic material to get into the cell.

The virus then disgorges its RNA core into the invaded cell, leaving the protein shell behind. The RNA then reprogrammes the cell's DNA to produce more copies of the virus. Links from stories in this section and more funding opportunities are available to subscribers on our research microsite at

www.thesis.co.uk Steve Farrar

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