RESUMO
Picorna-like plant viruses are non-enveloped RNA spherical viruses of ~30 nm. Part of the survival of these viruses depends on their capsid being stable enough to harbour the viral genome and yet malleable enough to allow its release. However, molecular mechanisms remain obscure. Here, we report a structure of a picorna-like plant virus, apple latent spherical virus, at 2.87 Å resolution by single-particle cryo-electron microscopy (cryo-EM) with a cold-field emission beam. The cryo-EM map reveals a unique structure composed of three capsid proteins Vp25, Vp20, and Vp24. Strikingly Vp25 has a long N-terminal extension, which substantially stabilises the capsid frame of Vp25 and Vp20 subunits. Cryo-EM images also resolve RNA genome leaking from a pentameric protrusion of Vp24 subunits. The structures and observations suggest that genome release occurs through occasional opening of the Vp24 subunits, possibly suppressed to a low frequency by the rigid frame of the other subunits.
Assuntos
Capsídeo/metabolismo , Genoma Viral , Secoviridae/química , Secoviridae/genética , Capsídeo/ultraestrutura , Chenopodium/virologia , Microscopia Crioeletrônica , Ligação Proteica , Estrutura Secundária de Proteína , Subunidades Proteicas/metabolismo , Secoviridae/ultraestruturaRESUMO
The genus Nepovirus (family Comoviridae) was known both for a good level of homogeneity and for the presence of atypical members. In particular, the atypical members of the genus differed by the number of capsid protein (CP) subunits. While typical nepoviruses have a single CP subunit with three structural domains, atypical nepoviruses have either three small CP subunits, probably corresponding to the three individual domains, or a large and a small subunit, probably containing two and one structural domains, respectively. These differences are corroborated by hierarchical clustering based on sequences derived from both genomic RNAs. Therefore, these atypical viruses are now classified in two distinct genera, Cheravirus (three CP subunits; type species Cherry rasp leaf virus) and Sadwavirus (two CP subunits; type species Satsuma dwarf virus).
Assuntos
Genoma Viral/genética , Vírus de Plantas/genética , Vírus de RNA/classificação , Secoviridae/classificação , Nepovirus/classificação , Filogenia , Vírus de Plantas/isolamento & purificação , Vírus de RNA/genética , Secoviridae/química , Secoviridae/genéticaAssuntos
Secoviridae/ultraestrutura , Sequência de Aminoácidos , Capsídeo/química , Capsídeo/ultraestrutura , Comovirus/química , Comovirus/genética , Comovirus/ultraestrutura , Cristalografia por Raios X , Genoma Viral , Microscopia Eletrônica , Modelos Moleculares , Dados de Sequência Molecular , Nepovirus/química , Nepovirus/genética , Nepovirus/ultraestrutura , Conformação Proteica , Secoviridae/química , Secoviridae/classificação , Secoviridae/genética , Homologia de Sequência de Aminoácidos , Eletricidade EstáticaRESUMO
The nucleotide sequences of genomic RNA1 (6795 nt) and RNA2 (5345 nt) of satsuma dwarf virus (SDV), a tentative member of the genus Nepovirus, were determined. The deduced genome organization of SDV showed similarities to the organization in como-, faba- and nepoviruses. There is extensive amino acid sequence similarity in the N-terminal regions of the proteins encoded by RNA1 and RNA2, as reported previously only for tomato ringspot nepovirus. However, unlike definitive nepoviruses, which have a single coat protein, SDV has two coat proteins. SDV RNA2 does not contain the long (> 1300 nt) 3' non-coding region characteristic of some nepoviruses. Phylogenetic analysis of SDV RNA polymerase placed SDV apart from como-, faba- and nepoviruses. These unique features suggest that SDV is distinct from the Comovirus, Fabavirus and Nepovirus genera, and needs to be separated into a new genus, probably within the family Comoviridae.
