Do All Spherical Viruses Have Icosahedral Symmetry?

TL;DR

This paper examines the symmetry of spherical viruses, suggesting that not all have icosahedral symmetry, especially for larger T-number viruses, and predicts specific deviations in their capsid structures.

Contribution

It challenges the assumption that all spherical viruses possess icosahedral symmetry, proposing alternative symmetries based on energy considerations and assembly principles.

Findings

High-resolution data may reveal non-icosahedral symmetry in T4 capsids.

Energy strain analysis suggests icosahedral symmetry becomes unlikely for larger T-number viruses.

Theoretical predictions indicate a need to reconsider virus capsid symmetry assumptions.

Abstract

Recent high resolution structures for viral capsids with 12, 32 and 72 subunits ($T1$, $T3$ and $T7$ viruses) have confirmed theoretical predictions of an icosadeltahedral structure with 12 subunits having five nearest neighbors (pentamers) and $(10T+2)-12$ subunits having six nearest neighbor subunits (hexamers). Here we note that theoretical considerations of energy strain for $T4$, $T9$ $T16$ and $T25$ viruses by aligned pentamers and energy strain along with the sheer number of possible arrangement of pentamers as the number of subunits grows, and simulations for such numbers of subunits make an icosadeltahedral configuration either miraculously unlikely or indicate that there must be a principle of capsid assembly of unprecedented fidelity in Nature. We predict, for example, that high resolution data will show $T4$ capsids to have $D_{5h}$ not icosahedral symmetry.