Electron cryomicroscopy and bioinformatics suggest protein fold models forrice dwarf virus

The three-dimensional structure of rice dwarf virus was determined to 6.8 A ngstrom resolution by single particle electron cryomicroscopy. By integrati ng the structural analysis with bioinformatics, the folds of the proteins i n the double-shelled capsid were derived. In the outer shell protein, the u niquely orientated upper and lower domains are composed of similar secondar y structure elements but have different relative orientations from that of bluetongue virus in the same Reoviridae family. Differences in both sequenc e and structure between these proteins may be important in defining virus-h ost interactions. The inner shell protein adopts a conformation similar to other members of Reoviridae, suggesting a common ancestor that has evolved to infect hosts ranging from plants to animals. Symmetry mismatch between t he two shells results in nonequivalent, yet specific, interactions that con tribute to the stability of this large macromolecular machine.