Proteomic and structural analysis of Tupanvirus deep ocean, a hairy monster from the deep

Giant viruses are the size of small bacteria and have double-stranded DNA genomes that are as long as the genomes of some small bacteria. Tupanvirus deep ocean (TVdo), a giant virus discovered in deep sea sediment, has a >1.4 Mbp genome that contains many genes associated with translation, a function that all viruses need their host to perform. Electron microscopic analyses of the virus extracted from infected Acanthamoeba castellanii show an icosahedral head with an approximate diameter of 400 nm and a wide (~300 nm diameter) cylindrical tail, both covered by thin fibrils radiating from the surface. Proteomic analysis of purified virions identified >220 viral proteins, including double jelly-roll capsid proteins similar to the adenovirus hexon, several proteins associated with transcription, and many uncharacterized proteins. These results suggest that TVdo enters its amoeba host ready to transcribe its genes. We identified two candidate fibril proteins from the large list of uncharacterized structural proteins based on their predicted structures from AlphaFold3. Infectivity assays, the insertion of a GFP transgene into the TVdo genome, and fluorescence microscopy will allow for future characterization of the viral infection cycle.