title: Structures of T=1 and T=3 particles of cucumber necrosis virus: evidence of internal scaffolding.
abstract: Cucumber necrosis virus (CNV) is a member of the genus Tombusvirus, of which tomato bushy stunt virus (TBSV) is the type member. The capsid protein for this group of viruses is composed of three major domains: the R domain, which interacts with the RNA genome: the S domain, which forms the tight capsid shell: and the protruding P domain, which extends approximately 40 Angstrom from the surface. Here, we present the cryo-transmission electron microscopy structures of both the T=1 and T=3 capsids to a resolution of approximately 12 Angstrom. The T=3 capsid is essentially identical with that of TBSV, and the T=1 particles are well described by the A subunit pentons from TBSV. Perhaps most notable is the fact that the T=3 particles have an articulated internal structure with two major internal shells, while the internal core of the T=1 particle is essentially disordered. These internal shells of the T=3 capsid agree extremely well in both dimension and character with published neutron-scattering results. This structure, combined with mutagenesis results in the accompanying article, suggests that the R domain forms an internal icosahedral scaffold that may play a role in T=3 capsid assembly. In addition, the N-terminal region has been shown to be involved in chloroplast targeting. Therefore, this region apparently has remarkably diverse functions that may be distributed unevenly among the quasi-equivalent A, B, and C subunits.
authors.affiliation: Donald Danforth Plant Science Center, 975 North Warson Road, St. Louis, MO 63132, USA.
authors.forename: Umesh
authors.initials: U
authors.lastname: Katpally
authors.forename: Kishore
authors.initials: K
authors.lastname: Kakani
authors.forename: Ron
authors.initials: R
authors.lastname: Reade
authors.forename: Kelly
authors.initials: K
authors.lastname: Dryden
authors.forename: D'Ann
authors.initials: D
authors.lastname: Rochon
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Smith
mesh_terms: D000595:Amino Acid Sequence; D036022:Capsid Proteins / Q000737:chemistry*; D018553:Cucumis sativus / Q000821:virology*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D017434:Protein Structure, Tertiary; D012367:RNA, Viral / Q000737:chemistry*; D017864:Tombusvirus / Q000737:chemistry*; D014771:Virion / Q000737:chemistry*
chemical_list: D036022:Capsid Proteins; D012367:RNA, Viral