RESUMO
TheL-A virus (LAV) particle is a specialized compartment for the transcription and replication of double-stranded RNA. It is 390 A in diameter and infects yeast. The particle is formed by a capsid containing 120 copies of a 680-residue gene product arranged with T = 1 icosahedral symmetry, approximately two copies of an RNA-directed RNA polymerase, and a 4.6-kb linear, duplex RNA. LAV crystals diffracting to at least 4.5-A resolution were grown in a combination of polyethylene glycol 8000, ethylene glycol, and lithium chloride. Following crystallization the reservoir solution was replaced by a 2x concentrated reservoir solution in order for ethylene glycol to function as a cryoprotectant even though initial crystals would not grow at sufficiently high concentrations of ethylene glycol for cryoprotection. A complete data set was collected to 6-A resolution from a frozen crystal obtained with this procedure. The crystals belong to space group P2(1). The unit cell dimensions are a = 406.7 A, b = 403.3 A, c = 572.5 A, beta = 90.3 degrees with two virus particles in the unit cell. The particle orientation was determined with the rotation function and the particle center was estimated on the basis of packing considerations.
Assuntos
RNA de Cadeia Dupla/genética , Saccharomyces cerevisiae/virologia , Totivirus/química , Vírion/química , Vírion/isolamento & purificação , Capsídeo/química , Cristalização , Dosagem de Genes , Produtos do Gene gag/genética , Produtos do Gene pol/genética , Peso Molecular , RNA Polimerase Dependente de RNA/genética , Difração de Raios X/métodosRESUMO
The extracellular bacteriolytic enzyme produced by Streptomyces globisporus shows a beta-1,4-N,6-O-diacetylmuramidase activity as well as a beta-1,4-N-acetylmuramidase activity. Crystals of this enzyme have been obtained by the hanging-drop vapour-diffusion method using polyethylene glycol as a precipitant. They belong to the tetragonal space group P4(1)2(1)2, with unit-cell parameters a = 63.11 (4), c = 121.1 (1) A, diffract to at least 2.0 A resolution and are suitable for high-resolution structure analysis. The crystal structure was solved by molecular replacement using lysozyme produced by S. erythraeus as a search model. The structure refinement is now in progress.
Assuntos
Muramidase/química , Streptococcus/enzimologia , Cristalização , Cristalografia por Raios X , Conformação ProteicaRESUMO
The crystal structure of tobacco necrosis virus (TNV) has been determined by real-space averaging with 5-fold non-crystallographic symmetry, and refined to R=25.3 % for diffraction data to 2.25 A resolution. A total of 180 subunits form a T=3 virus shell with a diameter of about 280 A and a small protrusion at the 5-fold axis. In 276 amino acid residues, the respective amino terminal 86, 87 and 56 residues of the A, B and C subunits are disordered. No density for the RNA was found. The subunits have a "jelly roll" beta-barrel structure, as have the structures of the subunits of other spherical viruses. The tertiary and quaternary structures of TNV are, in particular, similar to those of southern bean mosaic virus, although they are classified in different groups. Invisible residues 1 to 56 with a high level of basic residues are considered to be located inside the particle. Sequence comparison of the coat proteins of several TNV strains showed that the sequences of the disordered segment diverge considerably as compared with those of the ordered segment, consistent with a small tertiary structural constraint being imposed on the N-terminal segment. Basic residues are localized on the subunit interfaces or inner surface of the capsid. Positive charges of the basic residues facing the interior, as well as those of the N-terminal segment, may neutralize the negative charge of the RNA inside. Five calcium ions per icosahedral asymmetric unit are located at the subunit interfaces; three are close to the exterior surface, the other two away from it. The environments of the first three are similar, and those of the other two sites are similar. These calcium ions are assumed to be responsible for the stabilization/transition of the quaternary structure of the shell. Three peptide segments ordered only in the C subunits are clustered around each 3-fold (quasi-6-fold) axis forming a beta-annulus, and may lead to quasi-equivalent interactions for the organization of the T=3 shell.
Assuntos
Capsídeo/química , Capsídeo/metabolismo , Nicotiana/virologia , Vírus de Plantas/química , Plantas Tóxicas , Sequência de Aminoácidos , Sítios de Ligação , Cálcio/metabolismo , Cristalografia por Raios X , Modelos Moleculares , Dados de Sequência Molecular , Vírus de Plantas/genética , Estrutura Quaternária de Proteína , Estrutura Terciária de Proteína , Vírus de RNA/química , Vírus de RNA/genética , Alinhamento de Sequência , Montagem de Vírus , Água/metabolismoRESUMO
Rice dwarf virus crystals belong to space group I222 with cell parameters a = 770 (2), b = 795 (5), c = 814 (5) A and alpha = beta = gamma = 90 degrees. The unit cell of the crystal contains two viruses at the origin and body-centred positions. Using data synthesized from a rice dwarf virus model crystal in the space group I222, the possibility of ab initio phasing was thoroughly examined. The centric nature of the initial phases was unexpectedly broken by extensive iteration of the non-crystallographic symmetry averaging. The structure of rice dwarf virus was then solved with ab initio phasing up to 20 A resolution. The triangulation number determined by the present study is T = 13, which is different from the triangulation number, T = 9, previously determined by electron microscopy [Uyeda & Shikata (1982). Ann. Phytopathol. Soc. Jpn, 48, 295-300].