The structure of His-tagged Geobacillus stearothermophilus purine nucleoside phosphorylase reveals a `spanner in the works'.

The 1.72 Å resolution structure of purine nucleoside phosphorylase from Geobacillus stearothermophilus, a thermostable protein of potential interest for the biocatalytic synthesis of antiviral nucleoside compounds, is reported. The structure of the N-terminally His-tagged enzyme is a hexamer, as is typical of bacterial homologues, with a trimer-of-dimers arrangement.