4rpt

Publication Abstract from PubMed

Synthesis of 2' -5' -oligoadenylates (2-5A) by oligoadenylate synthetase (OAS) is an important innate cellular response that limits viral replication by activating the latent cellular ribonuclease, RNase L, to degrade single-stranded RNA. Some rotaviruses and coronaviruses antagonize the OAS/RNase L pathway through the activity of an encoded 2H phosphoesterase domain that cleaves 2-5A. These viral 2H phosphoesterases are phylogenetically related to the cellular A-kinase anchoring protein 7 (AKAP7) and share a core structure and an active site that contains two well-defined HPhi(S/T)Phi motifs, but their mechanism of substrate binding is unknown. Here we report the structures of a viral 2H phosphoesterase, the C-terminal domain (CTD) of the group A rotavirus VP3 protein, both alone and in complex with 2-5A. The domain forms a compact fold, with a concave beta-sheet that contains the catalytic cleft, but it lacks two alpha-helical regions and two beta-strands observed in AKAP7 and other 2H phosphoesterases. The co-crystal structure shows significant conformational changes in the "R-loop" upon ligand binding. Bioinformatics and biochemical analyses reveal that conserved residues and residues required for catalytic activity and substrate binding comprise the catalytic motifs and a region on one side of the binding cleft. We demonstrate that the VP3 CTD of group B rotavirus, but not that of group G, cleaves 2-5A. These findings suggest that the VP3 CTD is a streamlined version of a 2H phosphoesterase with a ligand-binding mechanism that is shared among 2H phosphodiesterases that cleave 2-5A. IMPORTANCE: The C-terminal domain (CTD) of rotavirus VP3 is a 2H phosphoesterase that cleaves 2' -5' -oligoadenylates (2-5A), potent activators of an important innate cellular antiviral pathway. 2H phosphoesterase superfamily proteins contain two conserved catalytic motifs and a proposed core structure. Here, we present structures of a viral 2H phosphoesterase, the rotavirus VP3 CTD, alone and in complex with its substrate, 2-5A. The domain lacks two alpha-helical regions and beta-strands present in other 2H phosphoesterases. A loop of the protein undergoes significant structural changes upon substrate binding. Together with our bioinformatics and biochemical findings, the crystal structures suggest that the RVA VP3 CTD domain is a streamlined version of a cellular enzyme that shares a ligand-binding mechanism with other 2H phosphodiesterases that cleave 2-5A, but differs from those of 2H phosphodiesterases that cleave other substrates. These findings may aid in the future design of antivirals targeting viral phosphodiesterases with cleavage specificity for 2-5A.

Structural basis for 2' -5' -oligoadenylate binding and enzyme activity of a viral RNase L antagonist.,Ogden KM, Hu L, Jha BK, Sankaran B, Weiss SR, Silverman RH, Patton JT, Prasad BV J Virol. 2015 Apr 15. pii: JVI.00701-15. PMID:25878106^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.