Structure and Function of the Rotavirus NSP2 Octamer, An Essential Component of the Viroplasm
Zenobia F. Taraporewala, Mukesh Kumar, B.V. Venkataram Prasad and John T. Patton
from: Segmented Double-stranded RNA Viruses: Structure and Molecular Biology (Edited by: John T. Patton). Caister Academic Press, U.K. (2008)
Viruses in the family Reoviridae produce cytoplasmic inclusion bodies (viroplasms) that serve as sites of genome packaging, replication and early stages of virion assembly. To support the complex events that occur in the viroplasm, the resident viral proteins must be dynamic and capable of multiple protein-protein and protein-RNA interactions. In rotavirus-infected cells, nucleation of viroplasms involves two nonstructural proteins, NSP2 and NSP5. NSP2 is a single-stranded (ss) RNA-binding protein with helix-destablizing, NTPase and RTPase activities. The protein self-assembles into doughnut-shaped octamers made up of two stacked tetramers. Electropositive grooves that span the surface of the octamer competitively bind two ligands, ssRNA and NSP5, providing a mechanism of modulating the activity of NSP2 between two functions. The NSP2 monomer contains a histidine-triad (HIT)-like fold that is shared by a large ubiquitous class of cellular nucleotide-binding proteins, one not previously seen in a viral protein. The HIT-like motif of the monomer is contained within a deep cleft that functions as the catalytic site for the hydrolytic activities of the protein. In this chapter, we review the current information on the structure of the NSP2 octamer, its catalytic activities, and the nature of its interactions with NTPs, ssRNA and other viral proteins. Based on these properties, we discuss potential roles for NSP2 in virus replication. Finally, the features of NSP2 are contrasted with the inclusion-forming proteins of other members of the Reoviridae read more ...