Rotavirus protein involved in genome replication and packaging exhibits a HIT-like fold

Rotavirus, the major cause of life-threatening infantile gastroenteritis, is a member of the Reoviridae1. Although the structures of rotavirus2 and other members of the Reoviridae3,4 have been extensively studied, little is known about the structures of virus-encoded non-structural proteins that are essential for genome replication and packaging. The non-structural protein NSP2 of rotavirus, which exhibits nucleoside triphosphatase, single-stranded RNA binding5, and nucleic-acid helix-destabilizing6 activities, is a major component of viral replicase complexes7,8. We present here the X-ray structure of the functional octamer9 of NSP2 determined to a resolution of 2.6 Å. The NSP2 monomer has two distinct domains. The amino-terminal domain has a new fold. The carboxy-terminal domain resembles the ubiquitous cellular histidine triad (HIT) group of nucleotidyl hydrolases10. This structural similarity suggests that the nucleotide-binding site is located inside the cleft between the two domains. Prominent grooves that run diagonally across the doughnut-shaped octamer are probable locations for RNA binding. Several RNA binding sites, resulting from the quaternary organization of NSP2 monomers, may be required for the helix destabilizing activity of NSP2 and its function during genome replication and packaging.