Determinants of Strain-Specific Differences in Efficiency of Reovirus Entry

Cell entry of reovirus requires a series of ordered steps, which include conformational changes in outer capsid protein mu 1 and its autocleavage. The mu 1N fragment released as a consequence of these events interacts with host cell membranes and mediates their disruption, leading to delivery of the viral core into the cytoplasm. The prototype reovirus strains T1L and T3D exhibit differences in the efficiency of autocleavage, in the propensity to undergo conformational changes required for membrane penetration, and in the capacity for penetrating host cell membranes. To better understand how polymorphic differences in mu 1 influence reovirus entry events, we generated recombinant viruses that express chimeric T1L-T3D mu 1 proteins and characterized them for the capacity to efficiently complete each step required for membrane penetration. Our studies revealed two important functions for the central delta region of mu 1. First, we found that mu 1 autocleavage is regulated by the N-terminal portion of delta, which forms an alpha-helical pedestal structure. Second, we observed that the C-terminal portion of delta, which forms a jelly-roll beta barrel structure, regulates membrane penetration by influencing the efficiency of ISVP* formation. Thus, our studies highlight the molecular basis for differences in the membrane penetration efficiency displayed by prototype reovirus strains and suggest that distinct portions of the reovirus delta domain influence different steps during entry.