GO:0004420 hydroxymethylglutaryl-CoA reductase (NADPH) activity: Mechanism, Genes and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0004420 describes the enzyme activity that catalyzes the reversible conversion of (S)-3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) to (R)-mevalonate, using NADPH as the electron donor.
• This activity is the rate-limiting step of the mevalonate pathway, which produces cholesterol, isoprenoids, dolichols, ubiquinone, and heme A.
• HMGCR is the pharmacological target of statins, which lower cholesterol and reduce cardiovascular events.
• The enzyme is regulated by transcriptional, translational, and post-translational mechanisms, including AMP-activated kinase and HMG-CoA reductase kinase.
• Dysregulation of HMGCR activity is linked to hypercholesterolemia, cardiovascular disease, and cancer.
• Researchers study this activity using spectrophotometric, radiometric, HPLC, and yeast-based assays.
Description
Hydroxymethylglutaryl-CoA reductase (NADPH) activity (GO:0004420) is a molecular function that catalyzes the committed step of the mevalonate pathway: the NADPH-dependent reduction of (S)-3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) to (R)-mevalonate. This reaction is the rate-limiting step for the biosynthesis of cholesterol and non-sterol isoprenoids, making it a central node in lipid metabolism and a major target for therapeutic intervention. The enzyme responsible, HMG-CoA reductase (HMGCR), is an integral membrane protein of the endoplasmic reticulum and is highly conserved from plants to humans. Because of its pivotal role, HMGCR activity is tightly regulated at multiple levels, and its dysregulation contributes to diseases such as hypercholesterolemia, atherosclerosis, and cancer. Understanding GO:0004420 is therefore essential for researchers in metabolism, cardiovascular biology, and drug discovery.
hydroxymethylglutaryl-CoA reductase (NADPH) activity At A Glance
| GO ID | GO:0004420 |
|---|---|
| GO term | hydroxymethylglutaryl-CoA reductase (NADPH) activity |
| Ontology | molecular_function |
| Synonym | HMG-CoA reductase activity; 3-hydroxy-3-methylglutaryl-coenzyme A reductase activity; hydroxymethylglutaryl-CoA reductase activity |
| Major function | Catalyzes the NADPH-dependent reduction of HMG-CoA to mevalonate, the rate-limiting step in cholesterol and isoprenoid biosynthesis |
| Reaction direction | Reversible; in vivo favors mevalonate formation |
| Cofactor | NADPH (two molecules per reaction) |
| Subcellular location | Endoplasmic reticulum membrane (in eukaryotes) |
| Pathway | Mevalonate pathway / cholesterol biosynthesis |
What Is GO:0004420?
GO:0004420 is defined as the catalysis of the reaction: (R)-mevalonate + CoA + 2 NADP+ = (S)-3-hydroxy-3-methylglutaryl-CoA + 2 H+ + 2 NADPH. In other words, it is the enzyme activity that interconverts HMG-CoA and mevalonate using NADPH as a cofactor. This activity is synonymous with HMG-CoA reductase activity and is the rate-limiting step in the mevalonate pathway.
Why Is hydroxymethylglutaryl-CoA reductase (NADPH) activity Important in Cell Biology?
GO:0004420 is critically important because it controls the flux through the mevalonate pathway, which supplies cholesterol and essential non-sterol isoprenoids such as farnesyl pyrophosphate, geranylgeranyl pyrophosphate, dolichol, ubiquinone, and heme A. These molecules are required for membrane integrity, protein prenylation, cell signaling, and mitochondrial function. Consequently, HMGCR activity is a major determinant of cardiovascular health, and its inhibition by statins is a cornerstone of cholesterol-lowering therapy. Moreover, altered HMGCR activity has been implicated in cancer, where mevalonate pathway intermediates support cell proliferation and survival.
• Rate-limiting enzyme of the mevalonate pathway, controlling cholesterol synthesis.
• Target of statins, the most widely prescribed cholesterol-lowering drugs.
• Provides isoprenoid precursors for protein prenylation, cell signaling, and mitochondrial electron transport.
• Dysregulation leads to hypercholesterolemia, atherosclerosis, and cardiovascular disease.
• Implicated in cancer cell proliferation and survival through mevalonate pathway intermediates.
• Essential in plants for synthesis of sterols, brassinosteroids, and other isoprenoids.
• Regulated by feedback mechanisms, hormones, and energy status.
• Studied as a model for enzyme kinetics and regulation of membrane-bound enzymes.
• Potential target for antiparasitic drugs in organisms like Hymenolepis diminuta.
• Used in metabolic engineering to boost squalene and other isoprenoid production in yeast.
What Happens During hydroxymethylglutaryl-CoA reductase (NADPH) activity?
Substrate Binding and Orientation
In simple terms: The enzyme grabs HMG-CoA and NADPH and positions them for reaction.
HMG-CoA reductase binds its substrate (S)-3-hydroxy-3-methylglutaryl-CoA and the cofactor NADPH in a defined active site. The enzyme is an integral membrane protein of the endoplasmic reticulum, and its catalytic domain faces the cytosol. Structural and kinetic studies indicate that the enzyme undergoes conformational changes upon substrate binding to facilitate hydride transfer from NADPH to the thioester carbonyl of HMG-CoA.
Catalytic Reduction and Mevalonate Formation
In simple terms: The enzyme uses NADPH to chemically convert HMG-CoA into mevalonate.
The catalytic mechanism involves the transfer of a hydride ion from NADPH to the thioester carbon of HMG-CoA, followed by the cleavage of the CoA thioester and the formation of mevalonate. Two molecules of NADPH are oxidized to NADP+ per molecule of mevalonate formed. This reaction is reversible in vitro, but in vivo the equilibrium favors mevalonate synthesis.
Regulation by Phosphorylation and Energy Status
In simple terms: The enzyme can be turned off by a chemical tag when energy is low.
HMG-CoA reductase activity is regulated by phosphorylation. AMP-activated protein kinase (AMPK) and a specific HMG-CoA reductase kinase phosphorylate the enzyme, reducing its activity. This provides a link between cellular energy status and cholesterol synthesis. Allosteric activation of the reductase kinase by nucleoside phosphates has been demonstrated in rat liver microsomes.
Feedback Control by Sterols and Isoprenoids
In simple terms: When cholesterol or related molecules are plentiful, the enzyme is slowed down.
The activity of HMG-CoA reductase is subject to feedback inhibition by sterols and non-sterol isoprenoids. Elevated levels of cholesterol or mevalonate-derived metabolites reduce enzyme activity through transcriptional and post-translational mechanisms. This ensures that the mevalonate pathway is not overactive when downstream products are abundant.
Key Genes Involved in GO:0004420 hydroxymethylglutaryl-CoA reductase (NADPH) activity
The following genes and proteins are directly or indirectly involved in hydroxymethylglutaryl-CoA reductase (NADPH) activity and its regulation.
| Gene | Major Role | Research Relevance |
|---|---|---|
| HMGCR | Encodes the rate-limiting enzyme of the mevalonate pathway; catalyzes HMG-CoA reduction | Target of statins; studied in cardiovascular disease and cancer |
| INSIG1 | Endoplasmic reticulum protein that binds HMGCR and promotes its degradation in response to sterols | Regulates HMGCR stability and cholesterol synthesis |
| INSIG2 | Similar to INSIG1; mediates sterol-dependent degradation of HMGCR | Modulates HMGCR activity and lipid homeostasis |
| SCAP | SREBP cleavage-activating protein; senses sterols and regulates SREBP processing | Controls transcription of HMGCR and other lipogenic genes |
| SREBF2 | Transcription factor that activates HMGCR and other cholesterol biosynthetic genes | Master regulator of cholesterol homeostasis |
| AMPK | Phosphorylates and inhibits HMGCR in response to low energy | Links energy status to cholesterol synthesis |
| HMGCS1 | Synthesizes HMG-CoA, the substrate for HMGCR | Upstream enzyme in mevalonate pathway |
| MVK | Mevalonate kinase; phosphorylates mevalonate downstream of HMGCR | Defects cause mevalonate kinase deficiency |
| PMVK | Phosphomevalonate kinase; converts mevalonate-5-phosphate to mevalonate-5-diphosphate | Part of mevalonate pathway |
| MVD | Mevalonate diphosphate decarboxylase; produces isopentenyl pyrophosphate | Downstream of HMGCR in isoprenoid synthesis |
| FDPS | Farnesyl diphosphate synthase; generates farnesyl pyrophosphate for sterols and prenylation | Uses isoprenoid products of mevalonate pathway |
| GGPS1 | Geranylgeranyl diphosphate synthase; produces geranylgeranyl pyrophosphate | Supports protein prenylation |
| SQLE | Squalene epoxidase; catalyzes a step in cholesterol biosynthesis | Downstream of HMGCR; target of terbinafine |
| LSS | Lanosterol synthase; cyclizes squalene to lanosterol | Cholesterol biosynthesis enzyme |
| CYP51A1 | Lanosterol 14-alpha demethylase; involved in sterol biosynthesis | Target of azole antifungals |
| DHCR7 | 7-dehydrocholesterol reductase; final step in cholesterol synthesis | Defects cause Smith-Lemli-Opitz syndrome |
| DHCR24 | 24-dehydrocholesterol reductase; involved in cholesterol synthesis | Associated with desmosterolosis |
| EBP | Emopamil binding protein; sterol isomerase in cholesterol biosynthesis | Mutations cause X-linked chondrodysplasia punctata |
How Is hydroxymethylglutaryl-CoA reductase (NADPH) activity Regulated?
HMG-CoA reductase (NADPH) activity is regulated at multiple levels. Transcriptionally, the SREBP-2 pathway activates HMGCR expression in response to sterol depletion. Post-translationally, the enzyme is phosphorylated and inhibited by AMP-activated protein kinase (AMPK) and a specific HMG-CoA reductase kinase, linking its activity to cellular energy status. Sterols and non-sterol isoprenoids feedback-inhibit the enzyme, and the ER proteins INSIG1 and INSIG2 mediate sterol-accelerated degradation of HMGCR. Additionally, allosteric activation of the reductase kinase by nucleoside phosphates has been reported.
hydroxymethylglutaryl-CoA reductase (NADPH) activity and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| HMGCR | Hypercholesterolemia, cardiovascular disease | Hmgcr knockout or point-mutation cell lines; statin response assays |
| HMGCR | Cancer cell proliferation | Cancer cell lines with HMGCR overexpression or knockout |
| HMGCR | Parasitic infection (Hymenolepis diminuta) | Parasite enzyme assays and inhibitor screening |
| INSIG1/2 | Dyslipidemia | Knockout cell models to study HMGCR degradation |
| SREBF2 | Cholesterol homeostasis disorders | Knockout or overexpression models to study HMGCR transcription |
Cardiovascular Disease and Hypercholesterolemia
HMGCR activity is the rate-limiting step in cholesterol synthesis, and its overactivity contributes to elevated LDL cholesterol and atherosclerosis. Statins, which competitively inhibit HMGCR, are widely used to lower cholesterol and reduce cardiovascular events. Studies in myocardial hypertrophy suggest that statins may also have pleiotropic effects beyond cholesterol lowering.
Cancer and Metabolic Reprogramming
Many cancer cells upregulate the mevalonate pathway to support rapid proliferation. HMGCR activity provides isoprenoid intermediates for protein prenylation and membrane synthesis, and its inhibition can reduce tumor growth in preclinical models. The enzyme is therefore considered a potential target for anticancer therapy.
Parasitic Infections
HMG-CoA reductase activity has been characterized in the tapeworm Hymenolepis diminuta, suggesting that the mevalonate pathway is essential for parasite survival and could be a target for antiparasitic drugs.
From hydroxymethylglutaryl-CoA reductase (NADPH) activity-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| Does loss of HMGCR affect cholesterol synthesis? | HMGCR knockout cell line (e.g., HepG2, HEK293) |
| How do point mutations in HMGCR affect statin sensitivity? | Point-mutation knock-in cell lines |
| Can HMGCR be tagged for live-cell imaging? | Knock-in of fluorescent tag (e.g., GFP) at HMGCR locus |
| Does HMGCR overexpression drive cancer cell proliferation? | HMGCR overexpression stable cell lines |
| What genes regulate HMGCR activity? | CRISPR library screening for modifiers of HMGCR activity |
| How does HMGCR activity affect isoprenoid production? | Yeast or mammalian cells with engineered mevalonate pathway |
How to Study the hydroxymethylglutaryl-CoA reductase (NADPH) activity Process
| Method | What It Measures | Typical Application |
|---|---|---|
| Spectrophotometric NADPH oxidation | Decrease in NADPH absorbance at 340 nm | Kinetic assays and inhibitor screening |
| Radiometric assay with 14C-HMG-CoA | Formation of 14C-mevalonate | Enzyme activity in tissues and cells |
| Reverse-phase HPLC | Mevalonate or HMG-CoA concentration | Direct quantification of enzyme activity |
| LC-MS/MS | Mevalonate and isoprenoid intermediates | Metabolic flux analysis |
| Western blot | HMGCR protein levels | Expression and degradation studies |
| qRT-PCR | HMGCR mRNA levels | Transcriptional regulation studies |
| Yeast growth complementation | Functional rescue of HMGCR deletion | Gene function validation |
Spectrophotometric Assays
HMG-CoA reductase activity can be measured spectrophotometrically by monitoring the oxidation of NADPH at 340 nm. This method is rapid and suitable for kinetic studies and inhibitor screening.
Radiometric Assays
Radiometric assays using labeled HMG-CoA (e.g., 14C-HMG-CoA) provide high sensitivity for measuring enzyme activity in tissue extracts and cell lysates.
HPLC-Based Assays
Reverse-phase HPLC can separate and quantify mevalonate or HMG-CoA, offering a direct and specific measurement of HMGCR activity.
Yeast Complementation and Metabolic Engineering
Yeast models expressing HMGCR can be used to study enzyme function and to engineer increased squalene or isoprenoid production.
How CRISPR Can Be Used to Study GO:0004420 hydroxymethylglutaryl-CoA reductase (NADPH) activity
Knockout
CRISPR knockout of HMGCR can be used to eliminate enzyme activity and study its role in cholesterol synthesis, cell proliferation, and isoprenoid production. HMGCR knockout cells may require exogenous mevalonate or cholesterol for survival, making them useful for studying pathway dependencies.
Point Mutation
Point mutations in HMGCR can be introduced to mimic naturally occurring variants or to alter catalytic residues, allowing researchers to dissect the enzyme's mechanism and statin sensitivity. For example, mutations in the catalytic domain can abolish activity, while mutations in the sterol-sensing domain can affect regulation.
Knock-in
Knock-in of tags (e.g., GFP, HA) or reporter genes at the HMGCR locus enables live-cell imaging, protein interaction studies, and monitoring of enzyme localization and turnover. Knock-in of disease-associated mutations can create isogenic models for drug testing.
Overexpression
CRISPR activation (CRISPRa) or stable overexpression of HMGCR can increase mevalonate pathway flux, leading to elevated cholesterol and isoprenoid production. This is useful for metabolic engineering and for studying the consequences of HMGCR overactivity in cancer and cardiovascular disease.
How EDITGENE Supports hydroxymethylglutaryl-CoA reductase (NADPH) activity Research
Researchers studying hydroxymethylglutaryl-CoA reductase (NADPH) activity-related genes often need to determine whether a candidate gene is causally involved in enzyme regulation, cholesterol synthesis, or disease. EDITGENE provides a comprehensive suite of CRISPR-based services to accelerate this research.
Contact EDITGENE today to design your custom CRISPR model for hydroxymethylglutaryl-CoA reductase (NADPH) activity research.
Frequently Asked Questions About hydroxymethylglutaryl-CoA reductase (NADPH) activity
What is hydroxymethylglutaryl-CoA reductase (NADPH) activity?
It is the enzyme activity that catalyzes the NADPH-dependent conversion of HMG-CoA to mevalonate, the rate-limiting step in cholesterol synthesis.
What genes are involved in hydroxymethylglutaryl-CoA reductase (NADPH) activity?
The primary gene is HMGCR, which encodes the enzyme. Other genes such as INSIG1, INSIG2, SREBF2, and AMPK regulate its expression and activity.
What is the GO ID for HMG-CoA reductase activity?
The Gene Ontology ID is GO:0004420.
How is HMG-CoA reductase activity measured?
Common methods include spectrophotometric NADPH oxidation, radiometric assays with 14C-HMG-CoA, and reverse-phase HPLC.
What diseases are associated with HMG-CoA reductase activity?
Hypercholesterolemia, cardiovascular disease, and cancer are linked to dysregulated HMGCR activity.
How do statins affect HMG-CoA reductase activity?
Statins competitively inhibit HMGCR, reducing cholesterol synthesis and lowering LDL cholesterol.
Is HMG-CoA reductase activity regulated by phosphorylation?
Yes, AMP-activated protein kinase and HMG-CoA reductase kinase phosphorylate and inhibit the enzyme.
Can CRISPR be used to study HMG-CoA reductase activity?
Yes, CRISPR knockout, point mutation, knock-in, and overexpression models are widely used to study HMGCR function and regulation.
What is the role of HMG-CoA reductase in plants?
In plants, HMGCR activity is essential for the synthesis of sterols, brassinosteroids, and other isoprenoids.
How does HMG-CoA reductase activity affect cancer?
Upregulated HMGCR activity supports cancer cell proliferation by providing isoprenoids for protein prenylation and membrane synthesis.
Conclusion
Hydroxymethylglutaryl-CoA reductase (NADPH) activity (GO:0004420) is a fundamental molecular function that controls the mevalonate pathway and thus cholesterol and isoprenoid biosynthesis. Its central role in cardiovascular disease and cancer makes it a prime target for therapeutic intervention and a focus of intense research. Understanding its mechanism, regulation, and disease connections requires robust experimental models, and CRISPR-based approaches offer powerful tools to dissect its function.
References
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- 3. Paramasivan K et al.. 2017. Regeneration of NADPH Coupled with HMG-CoA Reductase Activity Increases Squalene Synthesis in Saccharomyces cerevisiae.. J Agric Food Chem 65(37):8162-8170 PMID: 28845666
- 4. Nakagami H et al.. 2004. Statins and myocardial hypertrophy.. Coron Artery Dis 15(5):247-50 PMID: 15238820
- 5. Rao AV et al.. 1975. Indirect assessment of hydroxymethylglutaryl-CoA reductase (NADPH) activity in liver tissue.. Clin Chem 21(10):1523-5 PMID: 1157326
- 6. Fioravanti CF et al.. 1989. Hydroxymethylglutaryl coenzyme A reductase activity of adult Hymenolepis diminuta.. J Parasitol 75(5):653-7 PMID: 2795368
- 7. Mozzicafreddo M et al.. 2010. Rapid reverse phase-HPLC assay of HMG-CoA reductase activity.. J Lipid Res 51(8):2460-3 PMID: 20418539
- 8. Ferrer A et al.. 1987. Allosteric activation of rat liver microsomal [hydroxymethylglutaryl-CoA reductase (NADPH)]kinase by nucleoside phosphates.. Biol Chem Hoppe Seyler 368(3):249-57 PMID: 3689494
