Rotaviruses are nonenveloped icosahedral viruses with 11 double-stranded RNA gene segments inside a 70-nm triple-layered particle (TLP). Four capsid proteins, VP2, VP6, VP7, and VP4, are present in infectious TLPs. VP7 is the major structural protein on the surface of TLPs, while dimeric VP4 spikes project from the rotavirus surface. VP7 is the viral glycoprotein, while VP4 lacks signal sequences and posttranslational modifications. VP4 and VP7 are targets of neutralizing antibodies to rotaviruses, and immune responses to these proteins protect animals from disease.
Protease treatment of rotaviruses is required for viral infectivity. On the virion, trypsin cleaves VP4 (86 kDa) into the VP8^* (28 kDa) and VP5^* (60 kDa) proteins, activating the virus for infection. The VP4 and VP8^* proteins of some rotaviruses are capable of hemagglutination through viral attachment to sialic acid-containing cell surface components.