"To do these experiments, we need large amounts of undamaged virus, and the flaviviruses are difficult to culture," he says.
In addition, the flaviviruses can pose serious health risks to scientists who study them. Few scientific laboratories work with viruses from this family, and those that do either use a vaccine strain or an attenuated strain, modified to reduce the virulence of the virus. These precautions eliminate much of the risk, Rossmann says.
In their studies at Purdue, researchers used a dengue strain originally sequenced by scientists at the California Institute of Technology. Under the guidance of James Strauss, who is the Ethel Wilson and Robert Bowles Professor of Biology at Caltech, the group developed a strain of the virus that could be manipulated safely.
Studies of the dengue structure were done using the techniques of cryo-electron microscopy and three-dimensional image reconstruction. These techniques which use hundreds of highly detailed, two-dimensional images and powerful computer programs developed by Tim Baker at Purdue allowed the group to develop a three-dimensional view of the virus. A program developed by Rossmann was then used to interpret the three-dimensional images in terms of the viral molecular components.
The image shows how the major protein called "E" for envelope protein organizes itself to form a protective shell around the virus. The protein shell is made up of 60 subunits to form a 20-sided sphere. The shell serves as a cage for the genetic material inside, sheltering it from harm until it is released inside a host cell. While simple viruses consist of only a protein shell and genetic information, more complex viruses, such as flaviviruses, also contain a lipid bilayer that sits between the protein shell and viral genome.
Kuhn says the three-dimensional reconstruction reveals several unexpected features in the dengue virus architecture.
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Contact: Susan Gaidos
sgaidos@purdue.edu
765-494-2081
Purdue University
7-Mar-2002