Role of hydrogen and disulfide bonds in polyoma capsid structure

Abstract

The relationship between polyoma virus (Py) structure and function was studied. It was found that the virus was relatively stable under conditions which disrupt hydrogen and/or hydrophobic bonds, i.e., intermediate levels of concentrated urea, high pH, and heat. However, addition of the disulfide bond breaking reagents 2-mercaptoethanol or dithiothreitol (DTT), significantly potentiated the destructive effect of hydrogen bond disruption. Furthermore, it was found that the reaction with DTT was rate-limiting in the presence of urea but not at a pH of 10.5. This finding suggested that a barrier to the diffusion of DTT existed which was altered by alkaline treatment. Organic and inorganic mercurials were found not to influence viral function suggesting that free SH bonds were not structurally significant. Electron microscopy demonstrated that treatment at pH 10.5 followed by heating at 37° for 60 minutes, 56° for 30 minutes or with DTT caused the dissociation of virus particles into poorly resolved subunit material without recognizable capsomer structure. Following such extensive disaggregation, viral proteins no longer formed precipitin bands with anti-whole virus antiserum. A small plaque strain of Py was more susceptible than a large plaque strain to inactivation at pH 10.5 in the presence of DTT. These findings suggest that relatively inaccessible disulfide bridges contribute to the structural integrity of the virus particle and its immunochemically reactive antigenic determinants. Furthermore, differences between plaque size variants may be related in part to disulfide bond position or number.