Abstract
Although the nucleocytoplasmic large DNA viruses (NCLDVs) are one of the largest group of viruses that infect many eukaryotic hosts, the near-atomic resolution structures of these viruses have remained unknown. Here we describe a 3.5 Å resolution icosahedrally averaged capsid structure of Paramecium bursaria chlorella virus 1 (PBCV-1). This structure consists of 5040 copies of the major capsid protein, 60 copies of the penton protein and 1800 minor capsid proteins of which there are 13 different types. The minor capsid proteins form a hexagonal network below the outer capsid shell, stabilizing the capsid by binding neighboring capsomers together. The size of the viral capsid is determined by a tape-measure, minor capsid protein of which there are 60 copies in the virion. Homologs of the tape-measure protein and some of the other minor capsid proteins exist in other NCLDVs. Thus, a similar capsid assembly pathway might be used by other NCLDVs.
Highlights
The nucleocytoplasmic large DNA viruses (NCLDVs) are one of the largest group of viruses that infect many eukaryotic hosts, the near-atomic resolution structures of these viruses have remained unknown
These significant improvements in resolution of the Paramecium bursaria chlorella virus 1 (PBCV-1) cryo-EM map made it possible to model the viral capsid at near-atomic resolution (Supplementary Fig. 2)
Like the zip protein (P11) of PBCV-1, a previous cryo-EM study showed that the zip protein of Chilo irridescent virus (CIV) locates under the boundaries between neighboring symmetrons[7], presumably for gluing neighboring symmetrons together
Summary
The nucleocytoplasmic large DNA viruses (NCLDVs) are one of the largest group of viruses that infect many eukaryotic hosts, the near-atomic resolution structures of these viruses have remained unknown. Reported cryo-EM reconstructions of these approximately icosahedral NCLDVs are Paramecium bursaria chlorella virus 1 (PBCV-1)[4,5,6], Chilo irridescent virus (CIV)[4,7], Phaeocystis pouchetti virus (PpV01)[8], Melbourne virus[9], Cafeteria roenbergensis virus (CroV)[10], Acanthamoeba polyphaga mimivirus (APMV)[11], faustovirus[12], and pacmanvirus[13]. These cryo-EM reconstructions showed that these viruses have some common structural features. PBCV-1, a member in the chlorovirus genus of the family
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