Structures of minute virus of mice replication initiator protein N-terminal domain: Insights into DNA nicking and origin binding

- The structure of a parvovirus replication initiator protein has been determined;
- The structure sheds light on mechanisms of ssDNA binding and cleavage;
- The nickase active site is preconfigured for versatile metal ligand binding;
- The binding site for the double-stranded replication origin DNA is identified;
- A single domain integrates multiple functions in virus replication.

Members of the Parvoviridae family all encode a non-structural protein 1 (NS1) that directs replication of single-stranded viral DNA, packages viral DNA into capsid, and serves as a potent transcriptional activator. Here we report the X-ray structure of the minute virus of mice (MVM) NS1 N-terminal domain at 1.45 Å resolution, showing that sites for dsDNA binding, ssDNA binding and cleavage, nuclear localization, and other functions are integrated on a canonical fold of the histidine-hydrophobic-histidine superfamily of nucleases, including elements specific for this Protoparvovirus but distinct from its Bocaparvovirus or Dependoparvovirus orthologs. High resolution structural analysis reveals a nickase active site with an architecture that allows highly versatile metal ligand binding. The structures support a unified mechanism of replication origin recognition for homotelomeric and heterotelomeric parvoviruses, mediated by a basic-residue-rich hairpin and an adjacent helix in the initiator proteins and by tandem tetranucleotide motifs in the replication origins.

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