Phys. Rev. Appl. 7, 014005 (2017)

Credit: LAGUNA DESIGN/SCIENCE PHOTO LIBRARY

The genetic material of a virus is wrapped in a so-called capsid — a protective shell built from polypeptide chains. For half of the known viruses, the capsid's polypeptides are arranged into a structure with icosahedral symmetry, which is stabilized by the interplay between attractive and repulsive interactions in polypeptide subunits. Detailed knowledge of the parameters that govern these interactions enables an understanding not only of capsid formation, but also of their disassembly — important for devising strategies to prevent viral infection.

By mapping icosahedral capsid structures onto two-dimensional lattices, Guillaume Tresset and colleagues have found a way to describe the thermal dissociation of viral particles as a first-order phase transition. Monte Carlo simulations and a mean-field theory for capsid assembly led the authors to an analytical formula for the transition temperature as a function of the short-range attractive energy between subunits, their effective charge and the Debye screening length for the electrostatic interactions. Experiments with cowpea chlorotic mottle virus capsids (pictured), both empty and filled with RNA, corroborated the theoretical description — providing a promising starting point for developing viral disassembly inhibitors.