Modeling Microvirus Capsid Protein Evolution Utilizing Metagenomic Sequence Data

The Microviridae are increasingly becoming recognized as one of the most globally ubiquitous and highly diverse virus families, and as such, provide an advantageous model for studying virus evolution and adaptation. Here, we utilize microvirus sequences from diverse physiochemical environments, including novel sequences from a high-temperature acidic lake, to chart the outcome of natural selection in the main structural protein of the virus. Each icosahedral microvirus virion is composed of sixty identical capsid proteins that interact along twofold, threefold and fivefold symmetry axis interfaces to encapsidate a small, circular, single-stranded DNA genome. Viable assembly of the virus is guided by scaffolding proteins, which coordinate inter-subunit contacts between the capsid proteins. Structure-based analysis indicates that amino acid sequence conservation is predominantly localized to the twofold axis interface. While preservation of this quaternary interface appears to be essential, tertiary and secondary structural features of the capsid protein are permissive to considerable sequence variation.