Selection and characterization of a reovirus mutant with increased thermostability.

The environment represents a significant barrier to infection. Physical stressors (heat) or chemical agents (ethanol) can render virions noninfectious. As such, discrete proteins are necessary to stabilize the dual-layered structure of mammalian orthoreovirus (reovirus). The outer capsid participates in cell entry: (i) sigma 3 is degraded to generate the infectious subviral particle, and (ii) mu(1) facilitates membrane penetration and subsequent core delivery. mu(1)-sigma(3) interactions also prevent inactivation; however, this activity is not fully characterized. Using forward and reverse genetic approaches, we identified two mutations (mu(1) M258I and sigma 3 S344P) within heat- resistant strains. sigma 3 S344P was sufficient to enhance capsid integrity and to reduce protease sensitivity. Moreover, these changes impaired replicative fitness in a reassortant background. This work reveals new details regarding the determinants of reovirus stability. IMPORTANCE Nonenveloped viruses rely on protein- protein interactions to shield their genomes from the environment. The capsid, or protective shell, must also disassemble during cell entry. In this work, we identified a determinant within mammalian orthoreovirus that regulates heat resistance, disassembly kinetics, and replicative fitness. Together, these findings show capsid function is balanced for optimal replication and for spread to a new host.