Noncovalent interactions in viruses: Characterization of their role in the pH and thermally induced conformational changes in bromegrass mosaic virus
1973; Elsevier BV; Volume: 53; Issue: 1 Linguagem: Inglês
10.1016/0042-6822(73)90479-0
ISSN1096-0341
AutoresNino L. Incardona, Susan A. McKee, James B. Flanegan,
Tópico(s)Plant and Fungal Interactions Research
ResumoA study of the effect of temperature on the pH-induced structural transition in bromegrass mosaic virus revealed a thermal contribution to the process. Below pH 6.3 in 0.2 M KCl the S20,w is essentially constant over the range of 0–40 C. However, at pH 6.5 there is a dramatic change in both the S20,w and intrinsic viscosity with a Tm of about 35 C. This thermal portion is independent of the pH induced transition since it is irreversible while the latter is reversible. Moreover, in the presence of 0.005 M MgCl2 only the thermal portion is eliminated. When the same analysis is performed on reassembled BMV capsid, dissociation occurs as a function of pH at 5 C in both 0.20 M KCl and 0.067 M MgCl2. The midpoint of this dissociation is at a pH of approximately 5.7 in both solvents. No effect of temperature is observed on the hydrodynamic properties of the reassembled capsid. These results suggest that the pH-induced swelling of the virus is due to the titration of an abnormal carboxyl group which is involved in the protein-protein interactions between the subunits of the virus. The thermal contribution is postulated to be a result of a change in conformation of the viral RNA. A study of the ultraviolet and circular dichroism spectra as a function of temperature at pH 6.5 and 6.7 is consistent with this interpretation. In 0.20 M KCl the hyperchromism at 260 nm is at most 1% while there is a 7% decrease in ellipticity of the 265 nm positive dichroic band. This decrease is less in the presence of 0.005 M MgCl2. Thus, the change in the RNA conformation during the thermal swelling of the virus involves very little change in base stacking.
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