Mn2+ modulates the kinetic properties of an archaeal member of the PLL family

Recently we reported on the characterization of an archaeal member of the amidohydrolase superfamily, namely Sulfolobus acidocaldarius lactonase, showing low but significant and extremely thermostable paraoxonase activity. This enzyme, that we have named SacPox, is a member of the new described family of phosphotriesterase-like lactonases (PLLs). In this family the binuclear metal centre, which is involved in the catalytic machinery, has been poorly studied up to now. In this work we describe the expression of the protein in presence of different metals showing Mn2+ to support the higher activity. The enzyme has been over-expressed, purified and characterized as a Mn2+-containing enzyme by inductive plasma coupled mass spectrometry (ICP-MS), showing also surprising kinetic differences in comparison with the cadmium-containing enzyme. The Mn2+ containing enzyme was about 30-fold more efficient with paraoxon as substrate and more stable than the Cd2+ counterpart, even though the Mn2+ affinity for the binuclear metal centre is apparently lower. These results increase our knowledge of the biochemical characteristics of SacPox mainly with regard to the metal-ions modulation of function.

► Mn2+ ions are more effective than Cd2+ in sustaining promiscuous paraoxonase efficiency in SacPox. ► Mn2+ ions are more effective than Cd2+ ions in sustaining the stability of the active site. ► Mn2+ ions have lower affinity than Cd2+ for the metal centre as determined by ICP-MS and kinetic data.