The reovirus σ1 attachment protein influences the stability of its entry intermediate

Abstract

Structural metastability of viral capsids is pivotal for viruses to survive in harsh environments and to undergo timely conformational changes required for cell entry. Mammalian orthoreovirus (reovirus) is a model to study capsid metastability. Following initial disassembly of the reovirus particle mediated by proteases, a metastable intermediate called the infectious subvirion particle (ISVP) is generated. Using a {sigma}1 monoreassortant virus, we recently showed that {sigma}1 properties affect its encapsidation on particles and the metastability of ISVPs. How metastability is impacted by {sigma}1 and whether the lower encapsidation level of {sigma}1 is connected to this property is unknown. To define a correlation between encapsidation of {sigma}1 and ISVP stability, we generated mutant viruses with single amino acid polymorphisms in {sigma}1 or those that contain chimeric {sigma}1 molecules composed of {sigma}1 portions from Type 1 and Type 3 reovirus strains. We found that under most conditions where {sigma}1 encapsidation on the particle was lower, ISVPs displayed lower stability. By separating wild-type particles based on the level of encapsidated {sigma}1, we also found that lower {sigma}1 encapsidation leads to lower ISVP stability. Characterization of mutant viruses selected for enhanced stability via a forward genetic approach also revealed that in some cases, {sigma}1 properties influence stability without influencing {sigma}1 encapsidation. These data indicate that {sigma}1 can also influence ISVP stability independent of its level of incorporation. Together, our work reveals an underappreciated effect of the {sigma}1 attachment protein on the properties of the reovirus capsid.