POSTTRANSLATIONAL REGULATION OF MEVALONATE KINASE BY INTERMEDIATES OFTHE CHOLESTEROL AND NONSTEROL ISOPRENE BIOSYNTHETIC PATHWAYS

To assess the potential for feedback inhibition by isoprene intermedia tes in the cholesterol and nonsterol isoprene biosynthetic pathway, we expressed human cDNAs encoding mevalonate kinase (MKase), phosphomeva lonate kinase (PMKase), and mevalonate diphosphate decarboxylase (MDDa se) as fusion proteins in Escherichia coli DH5 alpha, and purified the se proteins by affinity chromatography. Several phosphorylated and non -phosphorylated isoprenes were analyzed as inhibitors of the enzymes u sing a standard spectrophotometric assay. Of the three proteins, only MKase was inhibited through competitive interaction at the ATP-binding site. The intermediates studied (and their relative inhibitory capaci ty) were: geranylgeranyl-diphosphate (GGPP, C-20) > farnesyl-diphospha te (FPP, C-15) > geranyl-diphosphate (GPP, C-10) > isopentenyl-diphosp hate (IPP, C-5) greater than or equal to 3,3-dimethylallyl-diphosphate (DMAPP, C-5) > farnesol (C-15) > dolichol-phosphate (DP, CSO-100) Mev alonate-diphosphate, geraniol, and dolichol were nor inhibitors; Our d ata further define die spectrum of physiologic inhibitors of MKase, an d provide the first evidence for feedback inhibition of MKase by a non sterol isoprene produced by the branched pathway, dolichol-phosphate. These results provide additional evidence that MKase may occupy a cent ral regulatory role in the control of cholesterol and nonsterol isopre ne biosynthesis.