Figure 1.

Effective potential energy (E; y axis) curves in the process of capsid swelling. In cases in which no conformational transition takes place, the energy increases continuously with the (relative) increase of capsid radius, ΔR/R (x axis). This is depicted by the full line. In cases in which protein conformational transitions occur, the energy switches from the dependence illustrated by the full line to the one illustrated by the dashed line at the point of the transition (CT). The conformational change illustrated in the figure induces a softening of the capsid. In both regimes, before and after the transition, Hookean elasticity is assumed to describe the swelling of the protein shell, as can be judged from the indicated parabolic dependence of energy on ΔR/R.