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Bovine Papillomavirus CryoEM Image Data
Subunit interactions in bovine papillomavirus.
Papillomaviruses, members of a group of dsDNA viruses associated with epithelial growths and tumors, have compact capsids assembled from 72 pentamers of the protein L1. We have determined the structure of bovine papillomavirus by electron cryomicrosopy (cryoEM), at ∼3.6 Å resolution. The density map, obtained from single-particle analysis of ∼4,000 particle images, shows the trace of the L1 polypeptide chain and reveals how the N- and C-terminal “arms” of a subunit (extensions from its β-jelly-roll core) associate with a neighboring pentamer. Critical contacts come from the C-terminal arm, which loops out from the core of the subunit, forms contacts (including a disulfide) with two subunits in a neighboring pentamer, and reinserts into the pentamer from which it emanates. This trace corrects one feature of an earlier model. We discuss implications of the structure for virion assembly and for pathways of infectious viral entry. We suggest that it should be possible to obtain image reconstructions of comparable resolution from cryoEM images of asymmetric particles. From the work on papillomavirus described here, we estimate that such a reconstruction will require about 1.5 million images to achieve the same number of averaged asymmetric units; structural variability will increase this number substantially.
Linked at right is a stack (16 GB) of 5,546 images (MRC/CCP4 format) of bovine papillomavirus (BPV ) collected at 300 kV and a calibrated magnification of 56,588, giving a pixel size on the specimen of 1.237 Å. Alignment parameters determined by Frealign for each particle in the stack can also be found below, as well as a reconstruction of BPV (also MRC/CCP4 format). Ewald sphere and beamtilt correction were performed. The atomic coordinates contain the coordinates from one subunit (3IYJ.pdb) and the five surrounding subunits to enable exploration of inter-subunit contacts.