GO:0106277 biliverdin reductase (NADPH) activity: Mechanism, Genes and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0106277 defines the molecular function that catalyzes the NADPH-dependent reduction of biliverdin IXalpha to bilirubin IXalpha, the final step in heme catabolism.
• The reaction consumes NADPH and produces bilirubin, a potent antioxidant and signaling molecule.
• Biliverdin reductase (BVR) activity is widely distributed across species and tissues, with distinct isoforms in mammals.
• Enzyme activity is sensitive to inhibition by heavy metals such as mercuric chloride, indicating critical sulfhydryl groups.
• Structural studies reveal a stacked-substrate mechanism essential for catalysis in cyanobacterial BVR.
• Dysregulated BVR activity is implicated in human diseases including renal carcinoma and oxidative stress-related pathologies.
Description
Biliverdin reductase (NADPH) activity, encoded by GO:0106277, is a molecular function that catalyzes the conversion of biliverdin IXalpha to bilirubin IXalpha using NADPH as an electron donor. This reaction constitutes the terminal step of heme degradation and is essential for the generation of bilirubin, a molecule with antioxidant and signaling properties. The enzyme is conserved across evolution, from cyanobacteria to mammals, and its activity has been detected in multiple tissues including liver, kidney, and spleen. Researchers study this activity to understand heme catabolism, oxidative stress responses, and the pathophysiology of diseases such as cancer and jaundice. The reaction is also of interest because bilirubin, the product, has been linked to protection against cardiovascular disease and neurodegeneration. Given its central role in redox biology, precise measurement and manipulation of biliverdin reductase (NADPH) activity are critical for both basic and translational research.
biliverdin reductase (NADPH) activity At A Glance
| GO ID | GO:0106277 |
|---|---|
| GO term | biliverdin reductase (NADPH) activity |
| Ontology | molecular_function |
| Synonym | biliverdin reductase (NADP+) activity |
| Major function | Catalyzes the NADPH-dependent reduction of biliverdin IXalpha to bilirubin IXalpha |
| Reaction | bilirubin IXalpha + NADP+ = biliverdin IXalpha + NADPH + H+ |
| Cofactor | NADPH |
| Substrate | Biliverdin IXalpha |
| Product | Bilirubin IXalpha |
What Is GO:0106277?
GO:0106277, biliverdin reductase (NADPH) activity, is defined as the catalysis of the reaction: bilirubin IXalpha + NADP+ = biliverdin IXalpha + NADPH + H+. In other words, it is the enzyme activity that reduces biliverdin IXalpha to bilirubin IXalpha using NADPH as the reducing agent, releasing NADP+ and a proton. This activity is synonymous with biliverdin reductase (NADP+) activity and is a key component of heme catabolism.
Why Is biliverdin reductase (NADPH) activity Important in Cell Biology?
Biliverdin reductase (NADPH) activity is essential for heme catabolism and the production of bilirubin, a molecule with potent antioxidant and cytoprotective effects. Dysregulation of this activity has been observed in human renal carcinoma, where enzyme levels are induced, suggesting a role in tumor biology. Moreover, the enzyme is sensitive to inhibition by heavy metals, linking it to environmental toxicity and oxidative stress. Understanding this activity is therefore crucial for elucidating mechanisms of redox homeostasis, disease progression, and potential therapeutic interventions.
• Final step in heme degradation, producing the antioxidant bilirubin.
• Bilirubin has been associated with protection against cardiovascular and neurodegenerative diseases.
• Enzyme activity is induced in human renal carcinoma, indicating a role in cancer.
• Inhibited by mercuric chloride, highlighting sensitivity to heavy metal toxicity.
• Conserved across species, facilitating comparative studies.
• Structural insights from cyanobacterial BVR inform mechanism and drug design.
• Essential for maintaining redox balance and cellular protection.
• Potential biomarker for oxidative stress-related conditions.
• Target for modulating bilirubin levels in jaundice and other disorders.
• Provides a model for studying NADPH-dependent oxidoreductases.
What Happens During biliverdin reductase (NADPH) activity?
Substrate Binding and Recognition
In simple terms: The enzyme grabs biliverdin and holds it in place.
Biliverdin reductase binds its substrate, biliverdin IXalpha, in a specific pocket. Structural studies of cyanobacterial BVR have shown that two substrate molecules stack in the active site, which is critical for activity. This stacking arrangement positions the biliverdin for efficient reduction. The enzyme exhibits high specificity for biliverdin IXalpha over other isomers.
NADPH Binding and Hydride Transfer
In simple terms: NADPH delivers a hydride to convert biliverdin to bilirubin.
The enzyme utilizes NADPH as a cofactor, which binds in a Rossmann-fold domain. The hydride from NADPH is transferred to the biliverdin substrate, reducing the central methine bridge. This step is essential for catalysis and is dependent on the presence of specific amino acid residues, as identified by chemical modification studies. The reaction produces bilirubin IXalpha, NADP+, and a proton.
Product Release and Enzyme Turnover
In simple terms: The enzyme releases bilirubin and resets for another cycle.
After reduction, bilirubin IXalpha is released from the active site. The enzyme then undergoes conformational changes to reset for another catalytic cycle. The activity can be measured using spectrophotometric assays that monitor the decrease in biliverdin absorbance or the increase in bilirubin. Turnover is influenced by pH and cofactor availability, as shown in studies of human renal carcinoma.
Regulation by Cellular Redox State
In simple terms: The cell's redox balance controls how active the enzyme is.
Biliverdin reductase activity is modulated by the cellular redox environment. The enzyme contains critical cysteine residues that are sensitive to oxidation and heavy metals such as mercuric chloride, which inhibits activity. This redox sensitivity suggests that the enzyme acts as a redox sensor, linking heme catabolism to oxidative stress responses.
Key Genes Involved in GO:0106277 biliverdin reductase (NADPH) activity
The following genes and proteins are directly involved in or regulate biliverdin reductase (NADPH) activity.
| Gene | Major Role | Research Relevance |
|---|---|---|
| BLVRA | Encodes biliverdin reductase A, the main enzyme for biliverdin IXalpha reduction | Target for studying heme catabolism and antioxidant defense |
| BLVRB | Encodes biliverdin reductase B, which reduces biliverdin IXbeta | Distinct substrate specificity; potential role in erythropoiesis |
| HMOX1 | Heme oxygenase 1, produces biliverdin from heme | Upstream regulator; often co-studied with BLVRA |
| HMOX2 | Heme oxygenase 2, constitutive isoform | Provides biliverdin for BVR under basal conditions |
| NADPH | Cofactor for the reduction reaction | Essential for enzyme activity; levels affect reaction rate |
| Biliverdin IXalpha | Substrate for the enzyme | Directly measures enzyme activity when monitored |
| Bilirubin IXalpha | Product of the reaction | Antioxidant and signaling molecule; readout of activity |
| Cysteine residues | Critical for catalytic activity and metal sensitivity | Site-directed mutagenesis targets |
| Serine residues | Active site serine in BVR-B maintains activity | Structural and functional studies |
| Mercuric chloride | Inhibitor of BVR activity | Used to probe active site cysteines |
| NADP+ | Product of the reaction | Can be used to monitor reverse reaction |
| BVR-A | Protein product of BLVRA | Major isoform in mammals; studied in cancer |
| BVR-B | Protein product of BLVRB | Isoform with distinct substrate preference |
| Cyanobacterial BVR | Model for structural studies | Revealed stacked substrate mechanism |
| Rat kidney BVR | Characterized enzyme source | Used for inhibition studies |
| Bovine BVR | Purified enzyme for kinetics | Comparative biochemistry |
| Human liver BVR | Purified isoforms for characterization | Clinical relevance |
How Is biliverdin reductase (NADPH) activity Regulated?
Biliverdin reductase (NADPH) activity is regulated at multiple levels. Enzyme abundance can be induced under conditions of oxidative stress, as seen in human renal carcinoma where activity is increased. The activity is also sensitive to inhibition by heavy metals such as mercuric chloride, which modifies critical cysteine residues. Additionally, the redox state of the cell influences the enzyme's catalytic efficiency, and cofactor availability (NADPH/NADP+ ratio) directly affects reaction rate. Structural studies suggest that substrate stacking and active site residues, including a serine in BVR-B, are important for maintaining activity.
biliverdin reductase (NADPH) activity and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| BLVRA | Renal carcinoma | Knockout of BLVRA in renal cell lines to assess proliferation and oxidative stress |
| BLVRA | Oxidative stress-related diseases | Overexpression of BLVRA in neuronal cells to test protection against ROS |
| BLVRB | Erythropoiesis and biliverdin IXbeta metabolism | Point mutations in active site serine to study substrate specificity |
| HMOX1 | Jaundice and hemolytic disorders | Co-knockout of HMOX1 and BLVRA to model bilirubin production |
| BVR (bacterial) | Structural mechanism | Crystallography of cyanobacterial BVR with substrate analogs |
Renal Carcinoma
Biliverdin reductase activity is induced in human renal carcinoma, with a pH and cofactor-specific increase in activity. This upregulation may reflect a cellular response to oxidative stress and could contribute to tumor antioxidant defenses. The enzyme's product, bilirubin, has been proposed to protect cancer cells from oxidative damage, suggesting a potential role in tumor progression.
Oxidative Stress and Neurodegeneration
Bilirubin, the product of biliverdin reductase, is a potent antioxidant that scavenges reactive oxygen species. Reduced BVR activity could lead to decreased bilirubin production and increased oxidative stress, which is implicated in neurodegenerative diseases. However, direct evidence linking BVR activity to neurodegeneration requires further investigation.
Heavy Metal Toxicity
Mercuric chloride inhibits biliverdin reductase activity by targeting critical cysteine residues. This inhibition may contribute to heavy metal-induced oxidative damage and toxicity. Understanding this interaction is important for assessing environmental health risks.
From biliverdin reductase (NADPH) activity-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| Does BLVRA knockout affect cellular antioxidant capacity? | BLVRA knockout cell line (e.g., HEK293) |
| What is the effect of a point mutation in the active site cysteine? | Point mutation knock-in of BLVRA Cys->Ser |
| Can tagged BLVRA be used to track subcellular localization? | Knock-in of FLAG-tagged BLVRA |
| Does overexpression of BLVRA protect against oxidative stress? | Overexpression of BLVRA in neuronal cells |
| What is the role of BLVRB in erythropoiesis? | Knockout of BLVRB in erythroid progenitor cells |
| How does mercuric chloride inhibit BVR activity? | In vitro enzyme assay with purified BVR and HgCl2 |
How to Study the biliverdin reductase (NADPH) activity Process
| Method | What It Measures | Typical Application |
|---|---|---|
| Spectrophotometric assay | Change in absorbance of biliverdin or bilirubin | Quantification of enzyme activity in cell lysates |
| X-ray crystallography | Three-dimensional structure of enzyme-substrate complex | Mechanistic studies and drug design |
| Site-directed mutagenesis | Effect of specific amino acid substitutions on activity | Identification of catalytic residues |
| Kinetic analysis | Km, Vmax, kcat | Characterization of enzyme efficiency |
| Western blot | Protein expression levels | Detection of BVR isoforms in tissues |
| Immunohistochemistry | Tissue distribution of BVR | Localization in normal and diseased tissues |
| qRT-PCR | mRNA expression of BLVRA/B | Transcriptional regulation studies |
| CRISPR knockout | Loss-of-function phenotype | Determining cellular roles of BVR |
Enzymatic Activity Assays
Biliverdin reductase activity is typically measured spectrophotometrically by monitoring the decrease in biliverdin absorbance at 670 nm or the increase in bilirubin absorbance at 450 nm. These assays require NADPH as a cofactor and can be performed with purified enzyme or cell lysates. The method is sensitive and can be adapted for high-throughput screening.
Structural Biology
X-ray crystallography and NMR spectroscopy have been used to determine the structure of biliverdin reductase, revealing a stacked substrate mechanism. These techniques provide atomic-level insights into substrate binding and catalysis, guiding mutagenesis studies.
Mutagenesis and Kinetic Analysis
Site-directed mutagenesis is employed to identify essential amino acid residues for activity. Kinetic parameters (Km, Vmax) are determined using purified mutant enzymes, revealing the roles of specific residues in catalysis and cofactor binding.
Expression and Purification
Recombinant biliverdin reductase can be expressed in E. coli or mammalian cells and purified using affinity chromatography. Purification allows for detailed biochemical characterization, including determination of molecular weight, isoelectric point, and cofactor specificity.
How CRISPR Can Be Used to Study GO:0106277 biliverdin reductase (NADPH) activity
Knockout
CRISPR-Cas9 knockout of BLVRA or BLVRB can be used to eliminate biliverdin reductase activity, enabling studies of its role in heme catabolism, oxidative stress, and cell survival. Knockout cell lines are valuable for assessing compensatory mechanisms and for validating inhibitor specificity.
Point Mutation
Point mutations in BLVRA, such as substitution of critical cysteine residues, can be introduced using CRISPR base editing or homology-directed repair to dissect the catalytic mechanism and metal sensitivity. These models help determine the contribution of specific residues to enzyme activity.
Knock-in
Knock-in of epitope tags (e.g., FLAG, HA) into the endogenous BLVRA locus allows for tracking of protein localization and interaction partners without overexpression artifacts. This approach preserves native regulation and stoichiometry.
Overexpression
CRISPR activation (CRISPRa) or lentiviral overexpression of BLVRA can be used to study the effects of increased biliverdin reductase activity on cellular antioxidant capacity and disease phenotypes. Overexpression models are useful for gain-of-function studies.
How EDITGENE Supports biliverdin reductase (NADPH) activity Research
Researchers studying biliverdin reductase (NADPH) activity-related genes often need to determine whether a candidate gene is causally involved in heme catabolism, oxidative stress, or disease. EDITGENE provides comprehensive CRISPR-based services to create precisely engineered cell models for such investigations.
Contact EDITGENE today to design your custom CRISPR model for biliverdin reductase (NADPH) activity research.
Frequently Asked Questions About biliverdin reductase (NADPH) activity
What is biliverdin reductase (NADPH) activity?
It is the enzyme activity that catalyzes the NADPH-dependent reduction of biliverdin IXalpha to bilirubin IXalpha, the final step in heme catabolism.
What genes are involved in biliverdin reductase (NADPH) activity?
The main genes are BLVRA (biliverdin reductase A) and BLVRB (biliverdin reductase B), which encode enzymes with distinct substrate specificities.
What is the reaction catalyzed by biliverdin reductase?
The reaction is: bilirubin IXalpha + NADP+ = biliverdin IXalpha + NADPH + H+.
How is biliverdin reductase activity measured?
It is typically measured spectrophotometrically by monitoring the decrease in biliverdin absorbance at 670 nm or the increase in bilirubin absorbance at 450 nm.
What diseases are associated with biliverdin reductase activity?
Altered activity has been observed in renal carcinoma and is implicated in oxidative stress-related diseases.
Is biliverdin reductase inhibited by heavy metals?
Yes, mercuric chloride inhibits biliverdin reductase activity by targeting critical cysteine residues.
What is the structure of biliverdin reductase?
Structural studies of cyanobacterial BVR revealed a stacked substrate mechanism essential for activity.
What is the difference between BLVRA and BLVRB?
BLVRA primarily reduces biliverdin IXalpha, while BLVRB reduces biliverdin IXbeta and has a distinct active site serine.
Can CRISPR be used to study biliverdin reductase?
Yes, CRISPR knockout, point mutation, knock-in, and overexpression models are powerful tools to study its function.
What is the role of bilirubin produced by this enzyme?
Bilirubin is a potent antioxidant and signaling molecule that may protect against cardiovascular and neurodegenerative diseases.
Conclusion
Biliverdin reductase (NADPH) activity (GO:0106277) is a critical molecular function in heme catabolism, responsible for producing bilirubin, a molecule with significant antioxidant and signaling roles. Its regulation and dysregulation are linked to cancer, oxidative stress, and heavy metal toxicity. Understanding this activity through biochemical, structural, and CRISPR-based approaches offers insights into redox biology and potential therapeutic targets. EDITGENE provides comprehensive CRISPR services to facilitate research on biliverdin reductase and its associated pathways.
References
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- 3. Takao H et al.. 2017. A substrate-bound structure of cyanobacterial biliverdin reductase identifies stacked substrates as critical for activity.. Nat Commun 8:14397 PMID: 28169272
- 4. Maines MD et al.. 1999. The oxidoreductase, biliverdin reductase, is induced in human renal carcinoma--pH and cofactor-specific increase in activity.. J Urol 162(4):1467-72 PMID: 10492239
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- 7. Chu WT et al.. 2017. Enzymatic Activity and Thermodynamic Stability of Biliverdin IXβ Reductase Are Maintained by an Active Site Serine.. Chemistry 23(8):1891-1900 PMID: 27897348
- 8. Yamaguchi T et al.. 1994. Biliverdin-IX alpha reductase and biliverdin-IX beta reductase from human liver. Purification and characterization.. J Biol Chem 269(39):24343-8 PMID: 7929092
