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2D phase transitions infect viruses


Researchers from the Laboratoire de Physique des Solides, the Institut de Chimie des Substances Naturelles and the Université François Rabelais have found a way to describe the thermal disassembly of viral particles as a first-order phase transition. By mapping the icosahedral capsid structure onto a two-dimensional lattice, the researchers have established an expression of the melting temperature as a function of the interaction parameters between subunits. Fluorescence experiments performed with a plant virus have validated the theoretical description.

The genetic material of a virus is packaged into a protective shell made up of polypeptide chains and called the capsid. For half of the known viruses, the polypeptides are arranged into a structure with an icosahedral symmetry stabilized by a delicate balance between attractive and repulsive interactions between the polypeptide subunits.

Crystal structure of the cowpea chlorotic mottle virus capsid (left) and two-dimensional lattice (right) used to reproduce thermal disassembly in Monte Carlo simulations.

Grand canonical Monte Carlo simulations and a mean-field theory have allowed the researchers to obtain an analytical expression for the melting temperature of a viral capsid as a funcion of the short-range attractive energy between subunits, their effective charge and the Debye screening length characteristic of the electrostatic interactions. Fluorescence experiments carried out with a plant virus – the cowpea chlorotic mottle virus (CCMV) – have corroborated the model and enabled the measurement of the interaction parameters between subunits, with both empty and genomic RNA-filled capsids. An accurate knowledge of the disassembly phenomena and of the interaction energies that come into play should prove itself essential in the development of disassembly inhibitors for therapeutic purpose.

Reference

Two-Dimensional Phase Transition of Viral Capsid Gives Insights into Subunit Interactions
Guillaume Tresset, Jingzhi Chen, Maelenn Chevreuil, Naïma Nhiri, Eric Jacquet, and Yves Lansac
Physical Review Applied 7, 014005 (2017)
doi:10.1103/PhysRevApplied.7.014005

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Guillaume Tresset