Enterococcus faecalis Acetoacetyl-Coenzyme A Thiolase/3-Hydroxy-3-Methylglutaryl-Coenzyme A Reductase, a Dual-Function Protein of Isopentenyl Diphosphate Biosynthesis†

AUTOR(ES)

Hedl, Matija

FONTE

American Society for Microbiology

RESUMO

Many bacteria employ the nonmevalonate pathway for synthesis of isopentenyl diphosphate, the monomer unit for isoprenoid biosynthesis. However, gram-positive cocci exclusively use the mevalonate pathway, which is essential for their growth (E. I. Wilding et al., J. Bacteriol. 182:4319-4327, 2000). Enzymes of the mevalonate pathway are thus potential targets for drug intervention. Uniquely, the enterococci possess a single open reading frame, mvaE, that appears to encode two enzymes of the mevalonate pathway, acetoacetyl-coenzyme A thiolase and 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase. Western blotting revealed that the mvaE gene product is a single polypeptide in Enterococcus faecalis, Enterococcus faecium, and Enterococcus hirae. The mvaE gene was cloned from E. faecalis and was expressed with an N-terminal His tag in Escherichia coli. The gene product was then purified by nickel affinity chromatography. As predicted, the 86.5-kDa mvaE gene product catalyzed both the acetoacetyl-CoA thiolase and HMG-CoA reductase reactions. Temperature optima, ΔHa and Km values, and pH optima were determined for both activities. Kinetic studies of acetoacetyl-CoA thiolase implicated a ping-pong mechanism. CoA acted as an inhibitor competitive with acetyl-CoA. A millimolar Ki for a statin drug confirmed that E. faecalis HMG-CoA reductase is a class II enzyme. The oxidoreductant was NADP(H). A role for an active-site histidine during the first redox step of the HMG-CoA, reductase reaction was suggested by the ability of diethylpyrocarbonate to block formation of mevalonate from HMG-CoA, but not from mevaldehyde. Sequence comparisons with other HMG-CoA reductases suggest that the essential active-site histidine is His756. The mvaE gene product represents the first example of an HMG-CoA reductase fused to another enzyme.

Documentos Relacionados

• Enterococcus faecalis 3-Hydroxy-3-Methylglutaryl Coenzyme A Synthase, an Enzyme of Isopentenyl Diphosphate Biosynthesis†
• Defect in biosynthesis of mitochondrial acetoacetyl-coenzyme A thiolase in cultured fibroblasts from a boy with 3-ketothiolase deficiency.
• Biogenesis of 3-hydroxy-3-methylglutaryl-coenzyme A reductase, an integral glycoprotein of the endoplasmic reticulum.
• Cholesterol-lowering effect of mevinolin, an inhibitor of 3-hydroxy-3-methylglutaryl-coenzyme a reductase, in healthy volunteers.
• In vivo modulation of rat liver 3-hydroxy-3-methylglutaryl-coenzyme A reductase, reductase kinase, and reductase kinase kinase by mevalonolactone.