Three-dimensional structure and stoichiometry of Helmintosporium victoriae190S totivirus.
Most double-stranded RNA viruses have a characteristic capsid consisting of 60 asymmetric coat protein dimers in a so-called T = 2 organization, a feature probably related to their unique life cycle. These capsids organize the replicative complex(es) that is actively involved in genome transcription and replication. Available structural data indicate that their RNA-dependent RNA polymerase (RDRP) is packaged as an integral capsid component, either as a replicative complex at the pentameric vertex (as in reovirus capsids) or as a fusion protein with the coat protein (as in some totivirus). In contrast with members of the family Reoviridae, there are two well-established capsid arrangements for dsRNA fungal viruses, exemplified by the totiviruses L-A and UmV and the chrysovirus PcV. Whereas L-A and UmV have a canonical T = 2 capsid, the PcV capsid is based on a T = 1 lattice composed of 60 capsid proteins. We used cryo-electron microscopy combined with three-dimensional reconstruction techniques and hydrodynamic analysis to determine the structure at 13.8 A resolution of Helminthosporium victoriae 190S virus (Hv190SV), a totivirus isolated from a filamentous fungus. The Hv190SV capsid has a smooth surface and is based on a T = 2 lattice with 60 equivalent dimers. Unlike the RDRP of some other totiviruses, which are expressed as a capsid protein-RDRP fusion protein, the Hv190SV RDRP is incorporated into the capsid as a separate, nonfused protein, free or non-covalently associated to the capsid interior.
Castón
José R
JR
Department of Estructura de Macromoléculas, Centro Nacional de Biotecnología, CSIC, Campus Universidad Autónoma de Madrid, Darwin no 3, Cantoblanco, E-28049 Madrid, Spain. jcraston@cnb.uam.es
Luque
Daniel
D
Trus
Benes L
BL
Rivas
Germán
G
Alfonso
Carlos
C
González
José M
JM
Carrascosa
José L
JL
Annamalai
Padmanaban
P
Ghabrial
Said A
SA
D002213:Capsid / Q000737:chemistry* / Q000378:metabolism; D020285:Cryoelectron Microscopy; D006375:Helminthosporium / Q000821:virology*; D021621:Imaging, Three-Dimensional; D019197:Totivirus / Q000737:chemistry*; D014771:Virion / Q000737:chemistry* / Q000145:classification