title: Interactions between the inner and outer capsids of bluetongue virus.
abstract: Bluetongue virus is a large and structurally complex virus composed of three concentric capsid layers that surround 10 segments of a double-stranded RNA genome. X-ray crystallographic analysis of the particles without the outer capsid layer has provided atomic structural details of VP3 and VP7, which form the inner two layers. However, limited structural information is available on the other five proteins in the virion-two of which are important for receptor recognition, hemagglutination, and membrane interaction-are in the outer layer, and the others, important for endogenous transcriptase activity are internal. Here we report the electron cryomicroscopy (cryo-EM) reconstruction of the mature particle, which shows that the outer layer has a unique non-T = 13 icosahedral organization consisting of two distinct triskelion and globular motifs interacting extensively with the underlying T = 13 layer. Comparative cryo-EM analysis of the recombinant corelike particles has shown that VP1 (viral polymerase) and VP4 (capping enzyme) together form a flower-shaped structure attached to the underside of VP3, directly beneath the fivefold axis. The structural data have been substantiated by biochemical studies demonstrating the interactions between the individual outer and inner capsid proteins.
authors.affiliation: Verna and Marrs McLean Department of Biochemistry and Molecular Biochemistry, Baylor College of Medicine, Houston, Texas 77030, USA.
authors.forename: Emma L
authors.initials: EL
authors.lastname: Nason
authors.forename: Rosalba
authors.initials: R
authors.lastname: Rothagel
authors.forename: Sharmila K
authors.initials: SK
authors.lastname: Mukherjee
authors.forename: Alak Kanti
authors.initials: AK
authors.lastname: Kar
authors.forename: Mario
authors.initials: M
authors.lastname: Forzan
authors.forename: B V Venkataram
authors.initials: BV
authors.lastname: Prasad
authors.forename: Polly
authors.initials: P
authors.lastname: Roy
mesh_terms: D001820:Bluetongue virus / Q000737:chemistry*; D002213:Capsid / Q000737:chemistry*; D036022:Capsid Proteins / Q000737:chemistry; D018360:Crystallography, X-Ray; D007091:Image Processing, Computer-Assisted; D008854:Microscopy, Electron; D014158:Transcription, Genetic; D014758:Viral Core Proteins / Q000737:chemistry
chemical_list: D036022:Capsid Proteins; C074954:VP3 protein, Bluetongue virus; D014758:Viral Core Proteins; C066862:VP7 protein, orbivirus