The refined structure of Nudaurelia capensis ω Virus reveals control elements for a T = 4 capsid maturation

AbstractLarge-scale reorganization of protein interactions characterizes many biological processes, yet few systems are accessible to biophysical studies that display this property. The capsid protein of Nudaurelia capensis ω Virus (NωV) has previously been characterized in two dramatically different T = 4 quasi-equivalent assembly states when expressed as virus-like particles (VLPs) in a baculovirus system. The procapsid (pH 7), is round, porous, and approximately 450 Å in diameter. It converts, in vitro, to the capsid form at pH 5 and the capsid is sealed shut, shaped like an icosahedron, has a maximum diameter of 410 Å and undergoes an autocatalytic cleavage at residue 570. Residues 571–644, the γ peptide, remain associated with the particle and are partially ordered. The interconversion of these states has been previously studied by solution X-ray scattering, electron cryo microscopy (CryoEM), and site-directed mutagenesis. The particle structures appear equivalent in authentic virions and the low pH form of the expressed and assembled protein. Previously, and before the discovery of the multiple morphological forms of the VLPs, we reported the X-ray structure of authentic NωV at 2.8 Å resolution. These coordinates defined the fold of the protein but were not refined at the time because of technical issues associated with the approximately 2.5 million reflection data set. We now report the refined, authentic virus structure that has added 29 residues to the original model and allows the description of the chemistry of molecular switching for T = 4 capsid formation and the multiple morphological forms. The amino and carboxy termini are internal, predominantly helical, and disordered to different degrees in the four structurally independent subunits; however, the refined structure shows significantly more ordered residues in this region, particularly at the amino end of the B subunit that is now seen to invade space occupied by the A subunits. These additional residues revealed a previously unnoticed strong interaction between the pentameric, γ peptide helices of the A and B subunits that are largely proximal to the quasi-6-fold axes. One C-terminal helix is ordered in the C and D subunits and stabilizes a flat interaction in two interfaces between the protein monomers while the other, quasi-equivalent, interactions are bent. As this helix is arginine rich, the comparable, disordered region in the A and B subunits probably interacts with RNA. One of the subunit–subunit interfaces has an unusual arrangement of carboxylate side chains. Based on this observation, we propose a mechanism for the control of the pH-dependent transitions of the virus particle

The epinet data of four Indian hospitals on incidence of exposure of healthcare workers to blood and body fluid: A multicentric prospective analysis

Background : Sharps injury (SI) and blood and body fluid exposure are occupational hazards to healthcare workers (HCWs). Although data from the developed countries have shown the enormity of the problem, data from developing countries, such as India, are lacking. Purpose : The purpose of this study was to cumulate data from fourmajor hospitals in India and analyze the incidence of SI and blood and body fluid exposure in HCWs. Materials and Methods : Four Indian hospitals (hospital A, B, C and D) from major cities of India participated in this multicentric study. Data ranging from 6 to 26 months were collected from these hospitals using Exposure Prevention Information network (EPINet) which is the database created by International Healthcare Worker Safety Research and Resource Center, University of Virginia. Results : Two hundred and forty-three sharp injuries and 22 incidents of blood or body fluid exposure were encountered in the cumulated 50 months of our study. The incidence of SIs was the highest among nurses (55%) of allthe HCWs, akin to the global data. An injury rate of nearly 20% among housekeeping staff seems to be specific to the Indian data. Patient′s room followed by operation theater appeared to be common locations of injury in our study. The source of the injury was identified in majority (64%) of the injuries. A major part of the group was not the primary users of the sharp (38%). Disposable needles caused nearly half of the injuries. Suture needles contributed to a reasonable number of injuries in one of the hospitals. Conclusions : The incidence of SI is the highest among nurses and the housekeeping staff (>30% each). A substantial number of injuries are avoidable

Symmetry of belladonna mottle virus: rotation function studies

Belladonna mottle virus, a spherical plant virus belonging to the tymovirus group, was crystallized by precipitation with polyethylene glycol 6000 in sodium citrate buffer (pH 5.6). The crystals belong to rhombohedral space group R3 (a \simeq 300 A, \alpha \simeq 60 °) with one molecule in the unit cell, and diffract X-rays to 3.5/~ resolution. Owing to the special interaxial angle of \simeq 60°, the lattice can also be described in terms of a pseudo-face-centred cubic cell. The face-centring vectors of the pseudo cell form the cell edges of the rhombohedral cell. The three-dimensional X-ray diffraction data on these crystals were collected using screenless oscillation photography to a resolution of 6 A. 37 842 independent reflections with {I/ \sigma (I) \geq 2-0} were measured on 51 filn ^pairs. The cell parameters were refined to a = 295.4A and \alpha = 59.86 ° by a postrefinement procedure. A rotation function was calculated using data between 11 and 13 A resolution. The function unambiguously reveals the particle icosahedral symmetry and orientation in the unit cell. The body diagonals of the pseudo-cubic cell are nearly tetrahedral. The icosahedral particle also has a set of tetrahedrally related threefold axes. The particle orientation is such that these two sets can be made coincident by a rotation of \simeq 180 ° about the rhombohedral [111] direction

Stability of belladonna mottle virus particles: the role of polyamines and calcium

The stability of belladonna mottle virus (BDMV) has been studied with respect to elevated pH and to freezing and thawing. BDMV, purified by a modified procedure, was stable at alkaline pH, in contradiction to earlier reports. This difference in the stability could be attributed to the presence of 90 to 140 molecules of spermidine, 20 to 50 molecules of putrescine and 500 to 900 calcium ions in each virus particle. The polyamines could be easily exchanged with other cations such as potassium or caesium and this resulted in a loss of particle stability. These cations may therefore play a role in maintaining the integrity of particle structure. The formation of empty protein shells as a result of freezing and thawing BDMV particles parallels earlier observations on turnip yellow mosaic virus particles