Polymer packaging and ejection in viral capsids: shape matters

TL;DR

This study uses mesoscale simulations to investigate how capsid shape influences polymer packaging and ejection, revealing that spherical shapes facilitate faster processes, especially for DNA-like semiflexible polymers, with implications for viral evolution.

Contribution

It provides new insights into how capsid geometry affects polymer dynamics, highlighting the evolutionary advantage of spherical shapes for viruses.

Findings

Flexible polymers eject more slowly from spheres than ellipsoids.

Semiflexible polymers, like DNA, are packaged and ejected more easily from spherical capsids.

Spherical capsids may have evolved to optimize genome ejection speed.

Abstract

We use a mesoscale simulation approach to explore the impact of different capsid geometries on the packaging and ejection dynamics of polymers of different flexibility. We find that both packing and ejection times are faster for flexible polymers. For such polymers a sphere packs more quickly and ejects more slowly than an ellipsoid. For semiflexible polymers, however, the case relevant to DNA, a sphere both packs and ejects more easily. We interpret our results by considering both the thermodynamics and the relaxational dynamics of the polymers. The predictions could be tested with bio-mimetic experiments with synthetic polymers inside artificial vesicles. Our results suggest that phages may have evolved to be roughly spherical in shape to optimise the speed of genome ejection, which is the first stage in infection.