Catalyzes the ATP dependent decarboxylation of (R)-5-diphosphomevalonate to form isopentenyl diphosphate (IPP). Functions in the mevalonate (MVA) pathway leading to isopentenyl diphosphate (IPP), a key precursor for the biosynthesis of isoprenoids and sterol synthesis. (R)-5-diphosphomevalonate + ATP = ADP + CO2 + isopentenyl diphosphate + phosphate Steroid biosynthesis; cholesterol biosynthesis. Homodimer. Belongs to the diphosphomevalonate decarboxylase family. Was originally thought to be located in the peroxisome. However, was later shown to be cytosolic.