STRUCTURE OF NORWALK VIRUS

Norwalk virus is the major cause of epidemic viral gastroenteritis of humans. Attempts to grow this virus in laboratory cell lines have been unsuccessful. However, the Norwalk virus capsid protein, when express ed in insect cells infected with a recombinant baculovirus, spontaneou sly assembles into virus-like particles. We have determined the 3-dime nsional structure of baculovirus-expressed Norwalk virus using electro n cryomicroscopy and computer image reconstruction to a resolution of similar to 22 Angstrom . These particles, having a diameter of 380 Ang strom, exhibit T=3 icosahedral symmetry. The 3-dimensional structure i s composed of 90 dimers of the 58000 molecular weight (58 K) capsid pr otein, each of which forms an arch-like capsomere. The structure of th e protein subunit is modular with three distinct domains. The distal g lobular domain that appears bilobed is connected to the lower shell do main by a central stem-like domain. We also have been able to grow cry stals of the baculovirus-expressed Norwalk virus particles suitable fo r high resolution X-ray crystallography.