Bacopa monniera recombinant mevalonate diphosphate decarboxylase: Biochemical characterization

Mevalonate diphosphate decarboxylase (MDD; EC 4.1.1.33) is an important enzyme in the mevalonic acid pathway catalyzing the Mg²⁺-ATP dependant decarboxylation of mevalonate 5-diphosphate (MVAPP) to isopentenyl diphosphate (IPP). Bacopa monniera recombinant MDD (BmMDD) protein was overexpressed in Escherichia coli BL21 (DE3) strain and purified to apparent homogeneity. K_m and V_max for MVAPP were 144μM and 52Umg^-1 respectively. The values of turnover (k_cat) and k_cat/K_m for mevalonate 5-diphosphate were determined to be 40s^-1 and 2.77×10⁵M^-1s^-1 and k_cat and k_cat/K_m values for ATP were found to be 30s^-1 and 2.20×10⁴M^-1s^-1, respectively. pH activity profile indicated the involvement of carboxylate ion, lysine and arginine for the activity of enzyme. The apparent activation energy for the BmMDD catalyzed reaction was 12.7kJmol^-1. Optimum pH and temperature for the forward reaction was found to be 8.0 and 45°C. The enzyme was most stable at pH 7 at 20°C with the deactivation rate constant (K_d^*) of 1.69×10^-4 and half life (t_1/2) of 68h. The cation studies suggested that BmMDD is a cation dependant enzyme and optimum activity was achieved in the presence of Mg²⁺.