Osmotic shock and the strength of viral capsids

Abstract

Osmotic shock is a familiar means for rupturing viral capsids and exposing their genomes intact. The necessary conditions for providing this shock involve incubation in high-concentration salt solutions, and lower permeability of the capsids to salt ions than to water molecules. We discuss here how values of the capsid strength can be inferred from calculations of the osmotic pressure differences associated with measured values of the critical concentration of incubation solution.

FIGURE 1

Osmotic equilibrium as a function of the presence and configuration of confined polyelectrolyte. (a) Inside and outside salt concentrations are the same when the permeable capsid is empty. (b) Confined fixed charge leads to higher counterion density inside, due to Donnan equilibrium effects. (c) These effects are amplified by further confinement of a stiff chain, by avoidance of strong bending.

FIGURE 2

Cell model depiction of fixed and mobile ion densities, inside and outside the hexagonally packed capsid (see text).