Viruses are the most abundant biological entity in the biosphere and are known to infect hosts from all domains of life. The aim of my work is to identify conserved and non-conserved features among the capsid structures of related and divergent icosahedral viruses via cryogenic electron microscopy, sequence analysis, molecular modeling, and other techniques. Bird polyomaviruses often cause severe disease in their hosts whereas mammalian polyomaviruses generally do not. Avian polyomavirus is a type of bird polyomavirus with an unusually broad host range compared to the restricted tropism of other polyomaviruses. Although most polyomaviruses have a conserved, rigid capsid protein structure, avian polyomavirus has a flexible capsid shell and a non-conserved C-terminus in its major capsid protein. A β-hairpin motif appears to stabilize other polyomaviruses but is missing in avian polyomavirus. The lack of this structure in avian polyomavirus may account for its capsid flexibility and broad host range. A minor capsid protein unique to bird polyomaviruses may be located on the inner capsid surface. This protein may have a role in the acute disease caused by bird polyomaviruses. The solution-state capsid structure of satellite tobacco mosaic virus was unexpectedly different than the previously solved crystalline structure. The conformational differences were accounted for by a shift of the capsid protein about the icosahedral fivefold axis. Conversely, the RNA core was consistent between solution and crystalline structures. The stable RNA core supports previous observations that the viral genome stabilizes the flexible capsid. Halophage CW02 infects Salinivibrio bacteria in the Great Salt Lake. The three-dimensional structure of CW02 revealed a conserved HK97-like fold that is found in all tailed, double-stranded DNA viruses. The capsid sequence of CW02 shares less than 20% identity with HK97-like viruses, demonstrating that structure is more conserved than sequence. A conserved module of genes places CW02 in the viral T7 supergroup, members of which are found in diverse aquatic environments. No tail structure was observed in reconstructions of CW02, but turret-like densities were found on each icosahedral vertex, which may represent unique adaptations similar to those seen in other extremophilic viruses.



College and Department

Physical and Mathematical Sciences; Chemistry and Biochemistry



Date Submitted


Document Type





cryogenic electron microscopy, halophage, icosahedral virus, polyomavirus, satellite tobacco mosaic virus, single-particle reconstruction, structural evolution