Quasi-Equilibrium Self-Assembly of Small RNA Viruses

TL;DR

This paper models the quasi-equilibrium self-assembly process of small ssRNA viruses, highlighting the interplay of electrostatic, hydrophobic, and tail-mediated interactions, and showing that traditional empty capsid theories are insufficient.

Contribution

It introduces a new theoretical framework for RNA virus assembly that accounts for RNA condensation and flexible tail interactions, extending beyond existing empty capsid models.

Findings

Assembly involves coupled phase transitions of capsid formation and RNA condensation.

Electrostatic, hydrophobic, and tail interactions determine assembly conditions.

Traditional empty capsid theories do not fully explain RNA-encapsidating virion assembly.

Abstract

We propose a description for the quasi-equilibrium self-assembly of small, single-stranded (ss) RNA viruses whose capsid proteins (CPs) have flexible, positively charged, disordered tails that associate with the negatively charged RNA genome molecules. We describe the assembly of such viruses as the interplay between two coupled phase-transition like events: the formation of the protein shell (the capsid) by CPs and the condensation of a large ss viral RNA molecule. Electrostatic repulsion between the CPs competes with attractive hydrophobic interactions and attractive interaction between neutralized RNA segments mediated by the tail-groups. An assembly diagram is derived in terms of the strength of attractive interactions between CPs and between CPs and the RNA molecules. It is compared with the results of recent studies of viral assembly. We demonstrate that the conventional theory of self-assembly, which does describe the assembly of \textit{empty} capsids, is in general not applicable to the self-assembly of RNA-encapsidating virions.