Near-atomic structure of a giant virus

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.

Chloroviruses

“…Recently, a 3.5 Å near-atomic resolution structure of PBCV-1 by cryoEM was reported [64]. This resolution was accomplished by correcting for the Ewald sphere effect in single cryoEM reconstructions [65].…”

“…The size of the viral capsid is predicted to be determined by a "tape measure" minor capsid protein (protein P2 (A342L) in Figure 4D) [64]. Currently, research efforts are focusing on identifying the proteins associated with the spike structure as well as the proteins involved in forming the fibers.…”

“…Each protein is shown in a different color as indicated on the right. Figures A and B are from Cherrier et al [61], Figure C is from Van Etten et al [27], and Figure D is from Fang et al [64]. All figures are published with permission.…”

The cryo-EM structure of African swine fever virus unravels a unique architecture comprising two icosahedral protein capsids and two lipoprotein membranes

“…underlying lipoprotein membrane that encloses the genomecontaining core (25,27,38,43). An exception to this overall structure is represented by Faustovirus, the closest relative of ASFV (7).…”

“…Many of the NCLDVs, including the phycodnavirus Paramecium bursaria Chlorella virus (PBCV-1) (25), the iridovirus Chilo iridescent virus (CIV) (26), the mimivirus Cafeteria roenbergensis virus (CroV) (27), or the giant amoeba-infecting Faustovirus (28), Pacmanvirus (11), and Medusavirus (29), present large icosahedral capsids composed of trimers of a MCP that displays a double jelly-roll fold. Each jelly-roll structure consists of eight anti-parallel ␤-strands arranged in two four-stranded sheets (30); the trimeric capsomer thus displays a pseudo-hexameric morphology.…”