Atomic structure reveals the unique capsid organization of a dsRNA virus

Abstract

For most dsRNA viruses, the genome-enclosing capsid comprises 120 copies of a single capsid protein (CP) organized into 60 icosahedrally equivalent dimers, generally identified as 2 nonsymmetrically interacting CP molecules with extensive lateral contacts. The crystal structure of a partitivirus, Penicillium stoloniferum virus F (PsV-F), reveals a different organization, in which the CP dimer is related by almost-perfect local 2-fold symmetry, forms prominent surface arches, and includes extensive structure swapping between the 2 subunits. An electron cryomicroscopy map of PsV-F shows that the disordered N terminus of each CP molecule interacts with the dsRNA genome and probably participates in its packaging or transcription. Intact PsV-F particles mediate semiconservative transcription, and transcripts are likely to exit through negatively charged channels at the icosahedral 5-fold axes. Other findings suggest that the PsV-F capsid is assembled from dimers of CP dimers, with an arrangement similar to flavivirus E glycoproteins.capsid assembly ͉ mycovirus ͉ Partitiviridae ͉ partitivirus

The T=1 Capsid Protein of Penicillium chrysogenum Virus Is Formed by a Repeated Helix-Rich Core Indicative of Gene Duplication

“…These two well-established tendencies among dsRNA virus CPs, based on their 3D atomic structures, have major consequences for the virus assembly pathway. Viruses of the first group (reo-, toti-, and chrysoviruses) are thought to be nucleated by pentamers of dimers, whereas partiti-and picobirnavirus capsids are probably assembled from dimers of CP dimers as intermediates (49). Strikingly, the capsid protein P1 of the dsRNA bacteriophage 8, a cystovirus, is found as a soluble tetramer (33) in an in vitro assembly system.…”

“…Partitiviruses and picobirnaviruses have a different quaternary organization, as the CP dimer has almost-perfect local 2-fold symmetry (18,49). These two well-established tendencies among dsRNA virus CPs, based on their 3D atomic structures, have major consequences for the virus assembly pathway.…”

“…1): the VP3 cores of the orbivirus bluetongue virus (BTV) (23), 1 cores of the reovirus in the genus Orthoreovirus (54), P3 of the rice dwarf virus (RDV) (46), the capsid shell protein (CPS) of the cytoplasmic polyhedrosis virus (CPV) (69), VP2 inner capsid of rotavirus (44) (all five Reoviridae), the CP of Penicillium stoloniferum virus F (PsV-F, of the family Partitiviridae) (49), the CP of picobirnavirus (PBV) (18), and Gag of the yeast L-A virus (45) (of the family Totiviridae). Sequence similarities among these viruses are negligible, and comparative analyses are inconclusive.…”

Structure of the hepatitis E virus-like particle suggests mechanisms for virus assembly and receptor binding

“…N562 is exposed to solvent at the very top of the surface spike and could potentially be subjected to glycosylation in the ER. The inner surface of the capsid shell is covered with a large number of basic amino acid side chains (R128, R133, R186, R189, R193, and R195, 6 from each subunit), remarkably different from dsRNA viruses in which a large number of negatively charged residues on the inner surface are used to facilitate the movement of dsRNA genome during particle-associated transcription [for an example, see (28)]. These arginine side chains from HEV-CP presumably help to neutralize the negative charges of the genomic RNA.…”

Structure of faustovirus, a large dsDNA virus

“…Multiple capsid layers can be found in the much smaller dsRNA T = 13 laevo rotaviruses (24,25) and in phi6 (26). A comparison between the spiky virus reconstruction and the reconstruction of the smooth inner capsid shows that the structure of the inner shell does not change significantly upon addition of the outer capsid layer.…”