Identification of H. volcanii Phosphomevalonate Decarboxylase and Isopentenyl Phosphate Kinase as Catalysts of the Terminal Enzymatic Reactions in an Archaeal Alternate Mevalonate Pathway (LB139)

Abstract

To identify the enzymes responsible for metabolism of mevalonate 5‐phosphate to isopentenyl diphosphate in H. volcanii, two open reading frames (HVO_2762; HVO_1412) were selected for expression and characterization. Characterization of these proteins indicates that one enzyme is an isopentenyl phosphate kinase that forms isopentenyl diphosphate. The second enzyme exhibits a decarboxylase activity that has never been directly attributed to this protein or any homologous protein. It catalyzes the synthesis of isopentenyl phosphate from mevalonate 5‐phosphate, a reaction proposed but never demonstrated by direct experimental proof. This enzyme, phosphomevalonate decarboxylase (PMD), exhibits strong inhibition by 6‐fluoromevalonate monophosphate but negligible inhibition by 6‐fluoromevalonate diphosphate (a potent inhibitor of the classical mevalonate pathway), reinforcing its selectivity for monophosphorylated ligands. Inhibition by the fluorinated analog also suggests that the PMD utilizes a reaction mechanism similar to that demonstrated for the classical MVA pathway decarboxylase. These observations represent the first experimental demonstration in H. volcanii of both the phosphomevalonate decarboxylase and isopentenyl phosphate kinase reactions that are required for an alternate mevalonate pathway in an archaeon. These results also represent, to the best of our knowledge, the first identification and characterization of an archaeal phosphomevalonate decarboxylase.