PMID: 27013661

Authors:

Li H, Hwang Y, Perry K, Bushman F, Van Duyne GD

Title:

Structure and metal-binding properties of a poxvirus resolvase.

Journal:

J Biol Chem. 2016 Mar 24. pii: jbc.M115.709139.

Abstract:

Poxviruses replicate their linear genomes by forming concatemers that must be resolved into monomeric units in order to produce new virions. A viral resolvase cleaves DNA 4-way junctions extruded at the concatemer junctions to produce monomeric genomes. This cleavage reaction is required for viral replication, so the resolvase is an attractive target for small molecule inhibitors. To provide a platform for understanding resolvase mechanism and designing inhibitors, we have determined the crystal structure of the canarypox virus (CPV) resolvase. CPV resolvase is dimer of RNase H superfamily domains related to E. coli RuvC, with an active site lined by highly conserved, acidic residues that bind metal ions. There are several intriguing structural differences between resolvase and RuvC and a model of the CPV resolvase.HJ complex provides insights into the consequences of these differences, including a plausible explanation for the weak sequence specificity exhibited by the poxvirus enzymes. The model also explains why the poxvirus resolvases are more promiscuous than RuvC, cleaving a variety of branched, bulged, and flap containing substrates. Based on the unique active site structure observed for CPV resolvase, we have carried out a series of experiments to test divalent ion usage and preferences. We find that the two resolvase metal binding sites have different preferences for Mg2+vs. Mn2+ Optimal resolvase activity is maintained with 5 muM Mn2+and 100 muM Mg2+, concentrations that are well below those required for either metal alone. Together, our findings provide biochemical insights and structural models that will facilitate studying poxvirus replication and the search for efficient poxvirus inhibitors.