Mevalonate pathway

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The mevalonate pathway or HMG-CoA reductase pathway or mevalonate-dependent (MAD) route, is an important cellular metabolic pathway present in all higher eukaryotes and many bacteria. It is important for the production of dimethylallyl pyrophosphate (DMAPP) and isopentenyl pyrophosphate (IPP) that serve as the basis for the biosynthesis of molecules used in processes as diverse as protein prenylation, cell membrane maintenance, hormones, protein anchoring and N-glycosylation.

Contents 1 Regulation and feedback 2 Pharmacology 3 Alternative 4 Reactions 5 References

[edit] Regulation and feedback

Several key enzymes can be activated through DNA transcriptional regulation on activation of SREBP (Sterol Regulatory Element-Binding Protein-1 and -2). This intracellular sensor detects low cholesterol levels and stimulates endogenous production by the HMG-CoA reductase pathway, as well as increasing lipoprotein uptake by up-regulating the LDL receptor. Regulation of this pathway is also achieved by controlling the rate of translation of the mRNA, degradation of reductase and phosphorylation.

For more information on regulation, see HMG-CoA reductase

[edit] Pharmacology

A number of drugs target the mevalonate pathway:

• Statins (used for elevated cholesterol levels);

[edit] Alternative

Plants and apicomplexan protozoa such as malaria parasites have the ability to produce their isoprenoids (terpenoids) using an additional alternative pathway called the methylerythritol phosphate (MEP) or non-mevalonate pathway which takes place in their plastids. In addition, most eubacteria including important pathogens such as Mycobacterium tuberculosis synthesize IPP and DMAPP via the non-mevalonate pathway instead.

[edit] Reactions

• Acetyl-CoA (citric acid cycle) is converted to acetoacetyl-CoA by the enzyme thiolase:

• Acetyl-CoA condenses with acetoacetyl-CoA to form 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA). This reaction is catalyzed by the enzyme HMG-CoA synthase.

• HMG-CoA is reduced to mevalonate by NADPH. This reaction occurs in the cytosol. It is the committed step in cholesterol synthesis, which is why the enzyme catalyzing the reaction, HMG-CoA reductase, is a target of statins.

• Mevalonate to 5-phosphomevalonate, catalyzed by the enzyme mevalonate kinase:

• 5-phosphomevalonate to 5-pyrophosphomevalonate, catalyzed by the enzyme phosphomevalonate kinase:

• Mevalonate-5-pyrophosphate to 3-isopentenyl pyrophosphate (IPP), catalyzed by the enzyme mevalonate-5-pyrophosphate decarboxylase (see also HIDS):

• 3-Isopentenyl pyrophosphate is isomerized to dimethylallyl pyrophosphate, catalyzed by the enzyme isopentenyl pyrophosphate isomerase:

[edit] References

1. Berg JM, Tymoczko JL, Stryer L. Biochemistry. 5th ed. New York: W.H. Freeman. xxxviii, 974, [976] (various pagings). ISBN 0-7167-4684-0.
2. Swanson KM, Hohl RJ. Anti-cancer therapy: targeting the mevalonate pathway. Curr Cancer Drug Targets 2006;6:15-37. PMID 16475974.