Biophysical Characterization of a Novel Phosphopentomutase from the Hyperthermophilic Archaeon .

Phosphopentomutases catalyze the isomerization of ribose 1-phosphate and ribose 5-phosphate. , a hyperthermophilic archaeon, harbors a novel enzyme (PPM) that exhibits high homology with phosphohexomutases but has no significant phosphohexomutase activity. Instead, PPM catalyzes the interconversion of ribose 1-phosphate and ribose 5-phosphate. Here, we report biophysical analysis, crystallization, and three-dimensional structure determination of PPM by X-ray diffraction at 2.39 Å resolution. The solved structure revealed a novel catalytic motif, unique to PPM, which makes this enzyme distinct from the homologous counterparts. We postulate that this novel catalytic motif may enable PPM to isomerize phosphopentose instead of phosphohexose. To the best of our knowledge, this is the first biophysical and structural analysis of a phosphopentomutase from hyperthermophilic archaea.