Rotavirus nonstructural protein NSP2 self-assembles into octamers that undergo ligand-induced conformational changes

The nonstructural protein NSP2 is a component of the rotavirus replication machinery and binds single-stranded RNA cooperatively, with high affinity, and independent of sequence, Recently, NSP2 has been shown to form multimer s and to possess an NTPase activity, but its precise function remains uncle ar. In the present study, we have characterized the solution structure of r ecombinant NSPS by velocity and equilibrium ultracentrifugation, dynamic li ght scattering, and circular dichroism spectroscopy. We found that NSP2 exi sts as an octamer, which is functional in the binding of RNA and ADP, In th e presence of magnesium, a partial dissociation of the octamer into smaller oligomers was observed, This was reversed by binding of ADP and RNA. We ob served an increased sedimentation rate in the presence of ADP and a nonhydr olyzable ATP analogue, which suggests a change toward a significantly more compact octameric conformation, The secondary structure of NSP2 showed a hi gh fraction of P-sheet, with small changes induced by magnesium that were r eversed in the presence of RNA. That NSP2 can exist in different conformati ons lends support to the previously proposed hypothesis (Taraporewala, Z,, Chen, D,, and Patton, J, T, (1999) J, Virol, 73, 9934-9943) of its function as a molecular motor involved in the packaging of viral mRNA.