Cryomicroscopy icosahedral structures

DETERMINATION OF ICOSAHEDRAL VIRUS STRUCTURES BY ELECTRON CRYOMICROSCOPY AT SUBNANOMETER RESOLUTION... 

Fig. 28-3. Structure of an alphavirus. Shown is the three-dimensional reconstruction of Sindbis virus at 28 A resolution from computer-processed images taken by electron cryomicroscopy, (a) The original electron micrograph shows virus particles in vitreous ice. (b) The surface view of the virus shows details of the 80 trimeric spikes, which are arranged in a T=4 icosahedron. Each spike protrudes 50 A from the virion surface and is believed to be composed of three E1-E2 glycoprotein heterodimers, (c) The cross-sectional view shows the outer surface spikes (yellow) and the internal nucleocapsid (blue), composed of the capsid and viral RNA. The space between the spikes and the nucleocapsid would be occupied by the lipid envelope. The green arrows mark visible points of interaction between the nucleocapsid and trans-membranal tails of the glycoprotein spikes, (d) The reconstructed capsid also exhibits a T=4 icosahedral symmetry. Computer models Courtesy of Angel M. Paredes, Cell Research Institute and Department of Microbiology, The University of Texas at Austin, Austin, Tex. Similar but not identical versions of these computer models were published in Paredes AM, Brown DT, Rothnagel R, et al. Three-dimensional structure of a membrane-containing virus. Proc Natl Acad Sci USA. 1993 90 9095-9099.

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