Fig. 4.

The spike. a–d show four views. One horn is shown with the raw density (yellow), whilst the other is clothed by eight VP3 pearl-like domains, where the density shown is averaged across all the pearls and the contour level is set to give the correct volume for a protein the size of VP3 (for details see text and Methods). Note that the pearl orientations present a common face to the concave inner surface of the horns, presumed to be the receptor-binding face. The contour level of the map raw density is set at a higher level, to make structural features clearer