MEVALONATE KINASE IS PREDOMINANTLY LOCALIZED IN PEROXISOMES AND IS DEFECTIVE IN PATIENTS WITH PEROXISOME DEFICIENCY DISORDERS

We reported recently that mevalonate kinase (EC 2.7.1.36; ATP:mevalona te 5-phosphotransferase) that was isolated from rat liver and believed to be a cytosolic protein was localized in rat liver peroxisomes. In addition, we found that the mevalonate kinase monoclonal antibody used in the study also reacted with several other proteins present in the mitochondrial and cytosolic fractions. These findings raised the prosp ect of the presence of several isoenzymes of mevalonate kinase localiz ed in different compartments of the cell. In the current study we prod uced four new polyclonal antibodies against different epitopes of meva lonate kinase to investigate the subcellular localization of the prote in by several different approaches: (i) by analytical subcellular frac tionation and immunoblotting of mevalonate kinase in the isolated subc ellular fractions with the monospecific antibodies; (ii) by immunocryo electron microscopy techniques; and (iii) by expressing the CDNA encod ing mevalonate kinase in maMmalian cells. The data obtained demonstrat e that there is only one mevalonate kinase protein that is predominate ly localized in peroxisomes. We also illustrate that the protein is ta rgeted to and imported into peroxisomes. In addition, we show that in cells and tissues obtained from patients with peroxisomal deficiency d iseases mevalonate kinase protein and its activity are severely reduce d.