New insight into the life cycle of the deadly Ebola virus could help the search for a cure. Researchers in France have worked out the structure of 'VP40', a clam-shaped protein less than five billionths of a metre long that forms the shell or 'matrix' of the Ebola virus.

"This will allow us to understand at last what makes this virus so devastating to humans," says Catherine Laughlin, at the US National Institutes of Health (NIH) in Bethesda, Maryland. "A drug directed at this target [VP40] should inhibit viral replication."

Six Ebola epidemics in Africa have been reported. When the Ebola virus infects cells it replicates in them and bursts out of them at a terrifying rate. This causes severe fever, pain, organ failure and bleeding -- victims have even been known to cry blood. The disease is untreatable and highly contagious once symptoms have developed, but how epidemics start is still unclear.

Yet, despite this potency, the Ebola virus has only seven genes -- compared to the thousands in a bacterium, or hundreds of thousands in a human. Understanding how such a simple organism can cause such catastrophic infection is the key to finding a cure.

Two weeks ago, NIH researchers reported that one of Ebola's genes makes infected cells produce a substance called 'glycoprotein'1. This protein destroys the walls of some cells, such as those that line blood vessels, and is apparently responsible for the bleeding associated with Ebola infection.

VP40 appears to be glycoprotein's partner in crime, Winfried Weissenhorn and colleagues at the European Molecular Biology Laboratory, Grenoble, France, now announce. VP40 may interact with glycoprotein in cell walls and assemble itself into new virus particles. There are then hundreds of new viruses just inside the cell, which are released as glycoprotein breaks it open.

Weissenhorn's team put the gene_ VP40_, that codes for the VP40 protein, into bacteria. These bacteria produced large amounts of the VP40 protein as they multiplied.

Then, by shining X-rays through crystals of purified VP40, Weissenhorn's group determined the exact atom-by-atom structure of the protein. X-rays bounce off atoms in the crystals, just as light glints off the faces of a diamond. The shape of a protein can then be inferred from the patterns made by this reflected and refracted light.

VP40 looks a bit like the two shells of a clam, the group explain in the EMBO Journal2. When a symmetrical VP40 protein binds to the wall of a cell, it opens up and forms links with six other nearby VP40s. These VP40 'hexamers' may be the building blocks for the shells of new viruses.

"We can now understand how other Ebola proteins interact with VP40 in the assembly of new viruses," says Yoshihiro Kawaoka of the School of Veterinary Medicine, Wisconsin, who stresses that this is one of the first matrix protein structures to be worked out. So, the shape of VP40 could also shed light on how other viruses grow.