Analysis of assembly mechanism of spherical virus based on its high resolution three-dimensional structure

Tobacco necrosis virus (TNV) is a spherical virus that contains ss-RNA (1.3x10 D16 d Da) as agenome. TNV causes such plants as C. quinoa and tulip necrotic lesions. TNV coat protein has 276amino acid residues；the amino acid sequence was determined by a combination of peptide and DNA sequencing. 180 copies ofthe protein assemble to form T=3 icosahedral shell. Thus，the virus shell has three stereochemically independent subunits (A，B and C) with identical primary structure.TNV crystallized in space group P4 D22 D232，with a=336.4 a . Unit cell contains two TNV particles. Diffraction data of TNV crystals were collectedto 2.25 A resolution using synchotron radiation and Weissenberg camera for macromolecules at BL6A，photon工厂情结(factory,Tsukuba. The structure was solved by averaging The electron density of非crystallographic unitsand refined by XPLOR to R=25.3%.The subunits have a fold of jelly roll β-barrel. Respectiven-terminal 86,87 and 56 residues of A，B和C subunits are disordered. The segment ordered only in C subunit （arm）产品diversity of the subunit interactions；A subunits form pentermers at five-fold axis，当B和C subunits form hexamers at icosahedral three-fold axis，where three arms of C-subunits form a β-annulus. Five calcium ion per icosahedral asymmetric unitwere identified. These are located at the subunit interfaces

Tobacco necrosis virus (TNV) is a spherical virus that contains ss-RNA (1.3x10ィイD16ィエD1 Da) as a genome. TNV causes such plants as C. quinoa and tulip necrotic lesions. TNV coat protein has 276 amino acid residues; the amino acid sequence was determined by a combination of peptide and DNA sequencing. 180 copies of the protein assemble to form T=3 icosahedral shell. Thus, the virus shell has three stereochemically independent subunits (A, B and C) with identical primary structure.TNV crystallized in space group P4ィイD22ィエD232, with a=336.4Å. Unit cell contains two TNV particles. Diffraction data of TNV crystals were collected to 2.25Å resolution using synchotron radiation and Weissenberg camera for macromolecules at BL6A, Photon Factory, Tsukuba. The structure was solved by averaging the electron density of non-crystallographic units and refined by XPLOR to R=25.3%.The subunits have a fold of jelly roll β-barrel. Respective N-terminal 86, 87 and 56 residues of A,B and C subunits are disordered. The segment ordered only in C subunit (arm) produces diversity of the subunit interactions; A subunits form pentermers at five-fold axis, whereas B and C subunits form hexamers at icosahedral three-fold axis, where three arms of C-subunits form a β-annulus. Five calcium ion per icosahedral asymmetric unit were identified. These are located at the subunit interfaces.