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Category: Applied and Industrial Microbiology
Effects of Hydrostatic Pressure on Viruses, Page 1 of 2
< Previous page | Next page > /docserver/preview/fulltext/10.1128/9781555815646/9781555814236_Chap02-1.gif /docserver/preview/fulltext/10.1128/9781555815646/9781555814236_Chap02-2.gifAbstract:
In several animal viruses, hydrostatic pressure causes inactivation with maintenance of immunogenicity. This chapter describes in detail how high pressure has been used to tackle basic and applied problems in virus biology. The contribution of protein folding and protein-nucleic acid interactions to virus assembly has been evaluated in many bacterial, plant, and animal viruses. Upon interaction with host cells, the conformations of the coat proteins and envelope glycoproteins have to change, which on one hand leads to noninfectious particles and on the other may lead to the exposure of previously occult epitopes, important for vaccine development. These irreversible conformational changes evoked by high pressure that resemble the changes that occur in vivo are discussed in the chapter for most of the viruses. It has been found that high pressure inactivates the enveloped influenza and Sindbis viruses by trapping the particles in the fusion intermediate state. The high titers of the neutralizing antibodies elicited by pressure-inactivated viruses indicate that hydrostatic pressure can be used to prepare whole-virus immunogens. The substantial evidence that high pressure traps viruses in the fusion intermediate states (found with alphaviruses, influenza virus, retroviruses, etc.), not infectious but highly immunogenic, is very promising for vaccine development.
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Cavity increase occurring in the M88V mutant. Using the program VMD and a probe radius of 1.4 Å, we analyzed the pdb coordinates of WT bacteriophage and the M88V mutant for the existence of internal cavities in this region. Shown is the region on coat protein in the asymmetric unit of the capsid around residue 88. For the WT phage structure (A), a significant cavity was identified in the neighboring region of the Met88 residue (B). After the replacement of this residue with valine (C), the cavity volume increased to 43 Å3 (D), reflecting a reduction in the surface area of the residue (59 Å2) and in the interactions occurring there (from reference 24 ).
Proposed model for the disassembly of picornaviruses by denaturing high concentrations of urea (A) or by pressure and low temperature (B). In panel A, a high urea concentration elicits complete dissociation and denaturation, with separation of the RNA from the coat protein (urea-unfolded subunits are represented as elongated random coils). In panel B, in contrast, pressure plus low temperature disrupts the icosahedral structure, but the capsid proteins (VP1, VP2, and VP3) still remain bound to the RNA. This particle loses infectivity upon returning to atmospheric pressure and room temperature. This infectivity loss may be due to release of VP4 and the pocket factor (from reference 29 ).
Pressure sensitivity of WT and cleavage-defective FHV VLPs. The pressure stability of FHV WT (circles) and D75N mutant (triangles) VLPs was analyzed by the shift of intrinsic fluorescence spectra (the spectral center of mass [A]) and particle average-size analysis (light scattering [B]). To better appreciate the effect of pressure, the reaction was poised by adding 1 M urea, a subdissociating concentration. Reassembly was evaluated by size exclusion high-performance liquid chromatography for WT FHV (C) and the mutant after decompression (D) (from reference 28 ). One bar is equal to 105 Pa.
Disassembly/denaturation of FHV by chemical and physical treatments. Shown is the proposed model for the reversible disassembly of FHV by pressure (a) and complete dissociation by high denaturing concentrations of urea (b). (c) Dissociation effect of high pressure and subdenaturing urea concentrations. (d and e) Effect of high temperature without and with subdenaturing (2 M) urea concentration, respectively. The high-temperature treatment induced aggregation of protein subunits. In panels b, c, and e, the treatments led to complete dissociation and denaturation with separation of the RNA from the capsid proteins, whereas high pressure induced disassembly of the particle, with the coat proteins remaining bound to the RNA (from reference 35 ).
pg 28 Gibbs free-energy and volume diagrams for enveloped viruses. Free-energy (A) and volume (B) diagrams showing the conversion between native nonfusogenic state (N) and fusogenic state (FG). The transition intermediate state (T) is also shown (from reference 16 ).
Pressure-induced fusogenic state of Sindbis virus. (A) Schematic representation of pressure-induced membrane fusion activation of Sindbis virus with ghosts. (B) Fusion assay of Sindbis virus with ghosts as measured by means of pyrene excimer/monomer fluorescence ratio intensity. Fusion was measured over a period of 1 h following addition of ghost vesicles to a final concentration of 0.5 mg/ml. □, native virus in the absence of ghosts at pH 7.5; 0, native virus in the presence of ghosts at pH 7.5;■, pressurized virus in the absence of ghosts at pH 7.5;▲, pressurized virus in the presence of ghosts at pH 7.5;●, virus in the presence of ghosts at pH 6.0. (C) Average values : standard deviations (error bars) after three 1-h experiments for all conditions described for panel (B). Column 1, native virus in the absence of ghosts at pH 7.5; column 2, native virus in the presence of ghosts at pH 7.5; column 3, pressurized virus in the absence of ghosts at pH 7.5; column 4, pressurized virus in the presence of ghosts at pH 7.5; column 5, virus in the presence of ghosts at pH 6.0. The pyrene-labeled lipids in the virus were excited at 330 nm, and the spectra were recorded at wavelengths from 360 to 530 nm. The fluorescence intensities of excimer and monomer emissions were determined at 470 and 389 nm, respectively. The virus concentration was 100 μg/ml (from reference 16 ).