GO:0008823 cupric reductase (NADH) activity: Mechanism, Genes and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0008823 (cupric reductase (NADH) activity) catalyzes the NADH-dependent reduction of two Cu2+ ions to two Cu+ ions, releasing one proton and NAD+.
• This activity is found in diverse organisms, from bacteria such as Escherichia coli and Thermotoga neapolitana to fungi like Candida albicans and Cryptococcus neoformans, and in mammals via Dcytb (Cybrd1).
• Cupric reductase (NADH) activity is distinct from ferric reductase activity, though some enzymes exhibit both activities.
• The reaction is important for copper homeostasis, iron uptake, and protection against copper toxicity.
• Dysregulation of copper reduction is linked to diseases including cancer and neurodegenerative disorders, though direct evidence for GO:0008823 in human disease is still emerging.
• Research tools include oxygen electrode assays, genetic knockouts, and heterologous expression for functional characterization.
Description
Cupric reductase (NADH) activity, defined by the Gene Ontology term GO:0008823, is a molecular function that catalyzes the reduction of cupric ions (Cu2+) to cuprous ions (Cu+) using NADH as the electron donor. This reaction is critical for copper homeostasis and for the acquisition of copper by cells, as Cu+ is often the preferred substrate for subsequent transport and incorporation into copper-dependent enzymes. The activity has been characterized in a wide range of organisms, including bacteria, fungi, algae, and mammals, highlighting its evolutionary conservation. Researchers study cupric reductase (NADH) activity to understand how organisms manage copper, a metal that is essential but toxic in excess, and to explore its roles in iron metabolism, oxidative stress, and host-pathogen interactions. The enzyme Dcytb (Cybrd1) in mammals exhibits both ferric and cupric reductase activities, linking copper and iron homeostasis. In pathogenic fungi such as Candida albicans and Cryptococcus neoformans, cupric reductase activity is regulated by copper levels and contributes to virulence. Thus, GO:0008823 represents a key biochemical function at the interface of metal metabolism and cellular physiology.
cupric reductase (NADH) activity At A Glance
| GO ID | GO:0008823 |
|---|---|
| GO term | cupric reductase (NADH) activity |
| Ontology | molecular_function |
| Synonym | none |
| Definition | Catalysis of the reaction: 2 Cu2+ + NADH = 2 Cu+ + H+ + NAD+. |
| Major function | Reduction of cupric ions to cuprous ions using NADH as electron donor |
| Organisms | Bacteria, fungi, algae, mammals |
| Cofactor | NADH (electron donor) |
| Subcellular location | Membrane-associated in many organisms |
What Is GO:0008823?
Cupric reductase (NADH) activity (GO:0008823) is defined as the catalysis of the reaction: 2 Cu2+ + NADH = 2 Cu+ + H+ + NAD+. In other words, it is an oxidoreductase that transfers electrons from NADH to cupric ions, converting them to cuprous ions while producing NAD+ and a proton. This activity is distinct from other cupric reductases that use different electron donors, such as NADPH.
Why Is cupric reductase (NADH) activity Important in Cell Biology?
Cupric reductase (NADH) activity is important because it controls the bioavailability of copper, a trace element essential for enzymes involved in respiration, iron metabolism, and antioxidant defense. By reducing Cu2+ to Cu+, it provides the substrate for high-affinity copper transporters and for incorporation into cuproproteins. In pathogens, this activity supports copper acquisition and resistance to copper toxicity, influencing virulence. In mammals, Dcytb (Cybrd1) contributes to both iron and copper reduction, linking the metabolism of these two metals. Dysregulation of copper reduction can lead to copper overload or deficiency, which are associated with diseases such as Wilson's disease, Menkes disease, and neurodegenerative disorders. Therefore, understanding GO:0008823 is crucial for metal homeostasis research and for developing therapies targeting copper metabolism.
• Essential for copper uptake and homeostasis in bacteria, fungi, and mammals.
• Provides Cu+ for copper-dependent enzymes and transporters.
• Contributes to iron metabolism via Dcytb (Cybrd1) in mammals.
• Supports virulence of pathogenic fungi by enabling copper acquisition.
• Protects cells from copper toxicity by regulating intracellular copper levels.
• Involved in host-pathogen interactions and immune defense.
• Potential target for antimicrobial and anticancer therapies.
• Links copper and iron homeostasis, impacting anemia and iron overload disorders.
• Studied in extremophiles like Thermotoga neapolitana for biotechnological applications.
• Serves as a model for understanding metalloreductase mechanisms.
Mechanism, Genes and Research Methods of cupric reductase (NADH) activity
Substrate Binding and Electron Transfer
In simple terms: The enzyme grabs NADH and cupric ions, then passes electrons from NADH to the copper.
The catalytic mechanism of cupric reductase (NADH) activity involves the binding of NADH and two Cu2+ ions. NADH serves as the electron donor, and electrons are transferred to Cu2+, reducing it to Cu+. This process likely involves a flavin or heme cofactor in some enzymes, as seen in Escherichia coli where the activity is linked to the respiratory chain. In Thermotoga neapolitana, membrane-associated redox activities suggest a similar electron transfer chain. The reaction produces NAD+ and a proton, and the resulting Cu+ can be used by copper chaperones or transporters.
Enzyme Diversity and Localization
In simple terms: Different organisms have different proteins that do this job, often located in the cell membrane.
Cupric reductase (NADH) activity is associated with various membrane-bound enzymes. In Candida albicans, the activity is cell-associated and regulated by iron and copper levels. In Cryptococcus neoformans, constitutive mutants show altered ferric/cupric reductase activities. The mammalian enzyme Dcytb (Cybrd1) is a membrane protein that functions as both ferric and cupric reductase in vitro. In the green alga Chlorella kessleri, iron-limited cells exhibit cupric reductase activity quantified via oxygen electrode. These enzymes are typically integral membrane proteins with extracellular or periplasmic active sites.
Regulation by Metal Availability
In simple terms: The amount of copper or iron around the cell controls whether the enzyme is active.
Cupric reductase (NADH) activity is regulated in response to metal levels. In Candida albicans, the activity is induced under iron limitation and repressed by copper, mediated by the transcription factor Mac1p. Similarly, in Cryptococcus neoformans, mutants with constitutive activity suggest a regulatory network responsive to copper and iron. In Chlorella kessleri, iron deficiency triggers cupric reductase activity, likely to enhance copper uptake for iron acquisition. This regulation ensures that cells acquire sufficient copper without accumulating toxic levels.
Physiological Roles in Copper and Iron Homeostasis
In simple terms: This enzyme helps cells get copper and iron, which are needed for many functions.
The primary physiological role of cupric reductase (NADH) activity is to reduce Cu2+ to Cu+, which is the substrate for high-affinity copper transporters like Ctr1. In mammals, Dcytb (Cybrd1) reduces both iron and copper, contributing to intestinal absorption. In pathogenic fungi, this activity is essential for copper acquisition during infection, as copper is a cofactor for superoxide dismutase and other virulence factors. In bacteria, the activity may be part of respiratory chains, influencing energy metabolism. Thus, GO:0008823 is central to metal homeostasis across kingdoms.
Key Genes Involved in GO:0008823 cupric reductase (NADH) activity
The following genes and proteins are directly associated with cupric reductase (NADH) activity or its regulation, as supported by published literature.
| Gene | Major Role | Research Relevance |
|---|---|---|
| Cybrd1 (Dcytb) | Ferric and cupric reductase in mammals | Links iron and copper metabolism; studied in intestinal absorption |
| Mac1p | Transcriptional regulator of copper-responsive genes in Candida albicans | Regulates cupric reductase activity in response to copper |
| RclA | Hypothiocyanite reductase in E. coli, may have cupric reductase activity | Potential overlap with cupric reduction; studied for redox functions |
| Ctr1 | High-affinity copper transporter | Uses Cu+ produced by cupric reductases for copper uptake |
| SOD1 | Copper-zinc superoxide dismutase | Requires copper; linked to cupric reductase for copper delivery |
| Cox1 | Cytochrome c oxidase subunit | Copper-dependent enzyme; cupric reductase supplies copper |
| Fet3 | Ferroxidase in yeast, coupled with iron reduction | Model for metal reduction and uptake |
| Fre1 | Ferric/cupric reductase in yeast | Homolog of cupric reductases; studied in iron uptake |
| NDH-1 | NADH dehydrogenase in respiratory chain | Linked to cupric reductase activity in E. coli |
| NDH-2 | Type II NADH dehydrogenase | May contribute to cupric reduction in bacteria |
| Cyc2 | Outer membrane cytochrome in acidophiles | Involved in extracellular electron transfer, potential cupric reduction |
| Mco1 | Multicopper oxidase in fungi | Works with reductases for copper homeostasis |
| Ctr4 | Copper transporter in Cryptococcus | Couples with cupric reductase for copper uptake |
| Cup1 | Copper-binding metallothionein | Protects against copper toxicity; regulated with reductases |
| Atox1 | Copper chaperone | Delivers Cu+ from reductases to ATP7A/B |
| ATP7A | Copper-transporting ATPase | Mutations cause Menkes disease; linked to copper reduction |
| ATP7B | Copper-transporting ATPase | Mutations cause Wilson's disease; copper homeostasis |
| Steap3 | Metalloreductase | Reduces iron and copper; potential cupric reductase |
How Is cupric reductase (NADH) activity Regulated?
Cupric reductase (NADH) activity is regulated primarily at the transcriptional level in response to metal availability. In Candida albicans, the copper-sensing transcription factor Mac1p activates genes involved in copper acquisition, including cupric reductases, under copper limitation. In Cryptococcus neoformans, constitutive mutants indicate a regulatory pathway that represses activity when copper is sufficient. Iron limitation also induces cupric reductase activity in Chlorella kessleri and Candida albicans, likely through iron-responsive transcription factors. Post-translational regulation may occur via redox state, as the activity depends on NADH availability and membrane integrity. In mammals, Dcytb (Cybrd1) expression is regulated by iron status and hypoxia, linking copper and iron homeostasis.
cupric reductase (NADH) activity and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| ATP7B | Wilson's disease (copper overload) | Hepatocyte KO or point mutation models |
| ATP7A | Menkes disease (copper deficiency) | Intestinal epithelial KO models |
| Cybrd1 (Dcytb) | Iron/copper metabolism disorders | Knockout mice or intestinal organoids |
| Mac1p | Fungal virulence (Candida albicans) | C. albicans mac1 deletion strains |
| STEAP3 | Cancer (overexpression in tumors) | Cancer cell lines with STEAP3 KO |
Copper Metabolism Disorders
Disorders of copper metabolism, such as Wilson's disease and Menkes disease, arise from mutations in copper-transporting ATPases ATP7B and ATP7A, respectively. Cupric reductase (NADH) activity, by producing Cu+ for these transporters, is indirectly involved in these diseases. Dcytb (Cybrd1) contributes to copper absorption, and its dysfunction may exacerbate copper imbalance. However, direct mutations in cupric reductase genes have not been definitively linked to these disorders, and further research is needed.
Cancer
Copper is required for angiogenesis and tumor growth, and copper chelators are being explored as anticancer agents. Cupric reductase (NADH) activity may influence copper availability in tumor cells, though direct evidence is limited. Some studies suggest that STEAP3, a metalloreductase, is overexpressed in certain cancers and may contribute to copper reduction. Targeting cupric reductases could disrupt copper homeostasis and inhibit tumor progression, but this remains speculative.
Neurodegeneration
Copper dyshomeostasis is implicated in neurodegenerative diseases such as Alzheimer's and Parkinson's, where copper interacts with amyloid-beta and alpha-synuclein. Cupric reductase (NADH) activity could modulate copper redox state, influencing oxidative stress. Dcytb (Cybrd1) is expressed in the brain, but its role in neurodegeneration is unclear. Further studies are needed to establish a direct link between GO:0008823 and these diseases.
Infectious Diseases
Pathogenic fungi like Candida albicans and Cryptococcus neoformans rely on cupric reductase (NADH) activity for copper acquisition and virulence. Inhibiting this activity could reduce fungal pathogenicity, making it a potential antifungal target. In bacteria, cupric reductases may contribute to survival in host environments, though specific roles are less defined.
From cupric reductase (NADH) activity-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| Does gene X encode a cupric reductase (NADH)? | Knockout cell line (e.g., HEK293) with activity assay |
| What is the subcellular localization of the enzyme? | Tagged knock-in (e.g., GFP) in mammalian cells |
| How does a point mutation affect catalytic activity? | Point mutation knock-in via CRISPR |
| Is the enzyme regulated by copper levels? | Overexpression and reporter assays in fungal models |
| Can the enzyme complement a yeast reductase mutant? | Heterologous expression in S. cerevisiae |
| What is the role of the enzyme in virulence? | Knockout in Candida albicans or Cryptococcus neoformans |
How to Study the cupric reductase (NADH) activity Process
| Method | What It Measures | Typical Application |
|---|---|---|
| BCA assay | Cu+ production from Cu2+ | Quantifying cupric reductase activity in cell lysates |
| Oxygen electrode | Oxygen consumption linked to NADH oxidation | Measuring activity in algae and bacteria |
| NADH oxidation assay | Decrease in NADH absorbance at 340 nm | Kinetic analysis of purified enzymes |
| RNA-seq | Transcript levels of copper-responsive genes | Studying regulation by Mac1p |
| CRISPR knockout | Loss of gene function | Confirming gene involvement in cupric reduction |
| Heterologous expression | Functional complementation | Testing candidate genes in yeast or E. coli |
| Fluorescence microscopy | Protein localization | Determining membrane association of reductases |
| ICP-MS | Intracellular copper content | Assessing copper uptake after reductase manipulation |
Enzymatic Activity Assays
Cupric reductase (NADH) activity is typically measured by monitoring the reduction of Cu2+ to Cu+ using a colorimetric reagent such as bicinchoninic acid (BCA) or by oxygen electrode. The assay requires NADH as electron donor and can be performed with cell lysates or membrane fractions. For example, Rapisarda et al. characterized the activity in E. coli respiratory chain using NADH oxidation. Weger et al. quantified cupric reductase activity in Chlorella kessleri via oxygen electrode.
Genetic Approaches
Genetic knockout or knockdown of candidate genes is used to confirm their role in cupric reductase activity. In Cryptococcus neoformans, constitutive mutants were isolated to study regulation. In Candida albicans, deletion of MAC1 altered cupric reductase activity. Heterologous expression in E. coli or yeast can be used to test if a gene encodes a functional cupric reductase.
Transcriptional and Proteomic Analysis
RNA-seq and qPCR can measure expression of genes involved in copper homeostasis under different metal conditions. Proteomics can identify membrane proteins associated with the activity. For instance, Woodacre et al. used transcriptional profiling to study Mac1p regulation. Meredith et al. used biochemical and genetic methods to characterize RclA in E. coli.
Imaging and Localization
Fluorescence microscopy with tagged proteins (e.g., GFP) can determine subcellular localization of cupric reductases. In mammalian cells, Dcytb (Cybrd1) was localized to the plasma membrane. Copper-sensitive fluorescent probes can also monitor intracellular copper levels in live cells.
How CRISPR Can Be Used to Study GO:0008823 cupric reductase (NADH) activity
Knockout
CRISPR knockout of candidate cupric reductase genes (e.g., CYBRD1, STEAP3) in human cell lines can abolish or reduce cupric reductase (NADH) activity, confirming their role. For example, knocking out CYBRD1 in intestinal cells would test its contribution to copper reduction. In fungal pathogens, knockout of MAC1 or reductase genes can attenuate virulence.
Point Mutation
Point mutations can be introduced to study catalytic residues or regulatory sites. For instance, mutating conserved histidines or cysteines in Dcytb (Cybrd1) may impair electron transfer. Such models help dissect the mechanism of GO:0008823.
Knock-in
Knock-in of tagged versions (e.g., GFP, HA) allows visualization and immunoprecipitation of cupric reductases. This is useful for localization studies and interactome analysis. For example, a GFP knock-in of CYBRD1 can reveal its trafficking in response to copper.
Overexpression
Overexpression of candidate genes in mammalian or microbial cells can increase cupric reductase activity, facilitating biochemical purification and kinetic studies. Overexpression of Dcytb (Cybrd1) in HEK293 cells enhanced both ferric and cupric reductase activities. In fungi, overexpression of MAC1 leads to upregulation of reductases.
How EDITGENE Supports cupric reductase (NADH) activity Research
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Frequently Asked Questions About cupric reductase (NADH) activity
What is cupric reductase (NADH) activity?
Cupric reductase (NADH) activity (GO:0008823) is a molecular function that catalyzes the reduction of two Cu2+ ions to two Cu+ ions using NADH as the electron donor, producing NAD+ and a proton.
What genes are involved in cupric reductase (NADH) activity?
Genes include CYBRD1 (Dcytb) in mammals, MAC1 in Candida albicans, and various bacterial and fungal reductases such as those in E. coli and Cryptococcus neoformans.
How is cupric reductase (NADH) activity measured?
It is measured by monitoring Cu+ production using colorimetric assays like BCA or by oxygen electrode, or by NADH oxidation at 340 nm.
What is the difference between cupric reductase and ferric reductase?
Cupric reductase reduces Cu2+ to Cu+, while ferric reductase reduces Fe3+ to Fe2+. Some enzymes, like Dcytb (Cybrd1), exhibit both activities.
Which organisms have cupric reductase (NADH) activity?
It is found in bacteria (E. coli, Thermotoga neapolitana), fungi (Candida albicans, Cryptococcus neoformans), algae (Chlorella kessleri), and mammals (Dcytb).
How is cupric reductase (NADH) activity regulated?
It is regulated transcriptionally by metal-responsive factors such as Mac1p in Candida albicans, and by iron and copper availability.
What diseases are associated with cupric reductase (NADH) activity?
Disorders of copper metabolism like Wilson's and Menkes diseases, as well as cancer and neurodegenerative diseases, may involve altered copper reduction, though direct links are still being investigated.
Can CRISPR be used to study cupric reductase (NADH) activity?
Yes, CRISPR knockout, point mutation, knock-in, and overexpression models can be used to study gene function and regulation of this activity.
What is the role of Dcytb (Cybrd1) in copper reduction?
Dcytb (Cybrd1) functions as both a ferric and cupric reductase in vitro, contributing to iron and copper absorption in mammals.
Why is cupric reductase (NADH) activity important for pathogens?
In pathogenic fungi, it enables copper acquisition for virulence factors and helps resist copper toxicity, making it a potential antifungal target.
Conclusion
Cupric reductase (NADH) activity (GO:0008823) is a fundamental biochemical function that reduces Cu2+ to Cu+, playing critical roles in copper homeostasis, iron metabolism, and host-pathogen interactions. Its presence across bacteria, fungi, algae, and mammals underscores its evolutionary importance. While direct links to human disease are still emerging, the activity is essential for normal physiology and represents a promising target for antimicrobial and anticancer strategies. Continued research using CRISPR models and biochemical assays will further elucidate its mechanisms and therapeutic potential.
References
- 1. Rapisarda VA et al.. 1999. Characterization of an NADH-linked cupric reductase activity from the Escherichia coli respiratory chain.. Arch Biochem Biophys 370(2):143-50 PMID: 10510271
- 2. Morrissey JA et al.. 1996. Candida albicans has a cell-associated ferric-reductase activity which is regulated in response to levels of iron and copper.. Microbiology (Reading) 142 ( Pt 3):485-492 PMID: 8868423
- 3. Weger HG et al.. 2007. Ferric and cupric reductase activities by iron-limited cells of the green alga Chlorella kessleri: quantification via oxygen electrode.. Physiol Plant 131(2):322-31 PMID: 18251903
- 4. Meredith JD et al.. 2022. Escherichia coli RclA is a highly active hypothiocyanite reductase.. Proc Natl Acad Sci U S A 119(30):e2119368119 PMID: 35867824
- 5. Käslin SA et al.. 1998. Membrane-associated redox activities in Thermotoga neapolitana.. Arch Microbiol 170(4):297-303 PMID: 9732444
- 6. Nyhus KJ et al.. 1999. Genetic and physiologic characterization of ferric/cupric reductase constitutive mutants of Cryptococcus neoformans.. Infect Immun 67(5):2357-65 PMID: 10225895
- 7. Wyman S et al.. 2008. Dcytb (Cybrd1) functions as both a ferric and a cupric reductase in vitro.. FEBS Lett 582(13):1901-6 PMID: 18498772
- 8. Woodacre A et al.. 2008. Copper-dependent transcriptional regulation by Candida albicans Mac1p.. Microbiology (Reading) 154(Pt 5):1502-1512 PMID: 18451059
