Biologically Relevant, Cationic Residues in Human Rhinovirus Stabilize Capsid-Bound RNA Duplexes, and Restrict Capsid Flexibility.

Abstract

Human rhinoviruses (RV) cause severe socioeconomic problems and are also associated to, or exacerbate, severe respiratory diseases, but no anti-RV drugs are available so far. Understanding the functional role(s) of capsid-RNA interactions in the RV virion may contribute to antiviral drug development. Our previous studies showed that the genome inside the RV-B14 virion is organized as a capsid-bound RNA dodecahedral cage formed by 30 intrachain RNA duplexes; and that positively charged capsid residues close to each RNA duplex, including K4058 and K2052, are involved in viral infection by promoting virion assembly and controlling genome uncoating. In this study, cryogenic electron microscopy was used to investigate the structural basis that underlies the functional roles of those positively charged residues in the RV virion. The atomic structure and equilibrium conformation dynamics of mutant virions carrying either K4058A or K2052A substitutions were compared with those of the parental RV-B14 virion under identical conditions. The results showed that both K4058 and K2052 residues stabilize the RNA duplex structure, and modulate capsid conformation and equilibrium dynamics. Notably, the partially disorganized RNA elements in the K4058A mutant virion strongly resemble those previously found by other researchers in an alternative wild-type RV-B14 structure. Comparison of the two alternative wild-type virion structures and the mutant virion structures supports the existence of two conformational states of the RV virion in the absence of cell receptor: a basal state with well-structured RNA duplexes, and an activated, RNA release-prone state in which the RNA duplexes are partially disorganized.