Do All Spherical Viruses Have Icosahedral Symmetry?

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.