GO:0141118 nitric oxide dioxygenase activity, heme protein as donor: Mechanism, Genes and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0141118 describes a molecular function in which a heme b-containing protein converts nitric oxide (NO) and oxygen into nitrate, thereby detoxifying NO.
• The reaction consumes Fe(II)-heme b and produces Fe(III)-heme b, linking NO detoxification to cellular redox and iron metabolism.
• Flavohemoglobins are the best-characterized enzymes with this activity, and they are widely used to study NO resistance in bacteria and fungi.
• Type I flavohemoglobin from Mycobacterium smegmatis is a functional nitric oxide dioxygenase, while type II flavohemoglobin has different electron-transfer properties.
• A novel hemoglobin in Acinetobacter baumannii confers resistance to host-derived NO, highlighting the role of this activity in pathogen survival.
• Studying GO:0141118 helps researchers understand microbial pathogenesis, host-pathogen interactions, and potential drug targets.
Description
Nitric oxide (NO) is a reactive free radical that serves as a signaling molecule in mammals but is also a key weapon used by the immune system to kill pathogens. To survive, many microorganisms express enzymes that detoxify NO. One such enzyme activity is nitric oxide dioxygenase activity, heme protein as donor, formally annotated as GO:0141118. This activity catalyzes the conversion of NO and oxygen to nitrate using a heme b cofactor, thereby protecting cells from nitrosative stress. The reaction is remarkable because it couples NO oxidation to the redox state of the heme iron, cycling between Fe(II) and Fe(III). Understanding this activity is important for researchers studying bacterial pathogenesis, host defense, and the evolution of globin proteins. Moreover, because NO is involved in diverse physiological processes, including vasodilation and neurotransmission, enzymes with this activity can influence host-microbe interactions and disease outcomes. This article provides a comprehensive overview of GO:0141118, covering its definition, mechanism, key genes, disease relevance, and experimental approaches.
nitric oxide dioxygenase activity, heme protein as donor At A Glance
| GO ID | GO:0141118 |
|---|---|
| GO term | nitric oxide dioxygenase activity, heme protein as donor |
| Ontology | molecular_function |
| Synonym | none |
| Major function | Catalysis of the reaction: Fe(II)-heme b-[protein] + nitric oxide + O2 = Fe(III)-heme b-[protein] + nitrate |
| Reaction direction | Forward reaction consumes NO and O2, produces nitrate |
| Cofactor | Heme b (iron-protoporphyrin IX) |
| Subcellular location | Cytosol (for many flavohemoglobins) |
| Representative enzymes | Flavohemoglobins (e.g., Hmp, Fhb) |
What Is GO:0141118?
GO:0141118, nitric oxide dioxygenase activity, heme protein as donor, is a molecular function defined by the reaction: Fe(II)-heme b-[protein] + nitric oxide + O2 = Fe(III)-heme b-[protein] + nitrate. In other words, a protein-bound heme iron in the ferrous state (Fe(II)) reacts with nitric oxide and molecular oxygen to produce nitrate, while the heme iron becomes oxidized to the ferric state (Fe(III)). This activity is a type of dioxygenase because both atoms of molecular oxygen are incorporated into the product, nitrate. The term is specific to heme proteins that act as the electron donor, distinguishing it from other NO-metabolizing enzymes.
Why Is nitric oxide dioxygenase activity, heme protein as donor Important in Cell Biology?
GO:0141118 is important because it represents a primary mechanism by which microorganisms defend themselves against nitric oxide, a central component of innate immunity. By detoxifying NO to nitrate, pathogens such as Mycobacterium smegmatis and Acinetobacter baumannii can survive within host macrophages and cause disease. This activity also plays a role in global nitrogen cycling and in the response to nitrosative stress. For researchers, understanding this activity provides insights into microbial pathogenesis, host-pathogen interactions, and potential targets for antimicrobial therapy.
• Enables pathogens to resist host-derived nitric oxide, a key antimicrobial weapon.
• Contributes to bacterial survival within macrophages and other host niches.
• Represents a validated drug target for overcoming NO resistance in pathogens.
• Links NO detoxification to cellular redox homeostasis and iron metabolism.
• Provides a model system for studying heme-based catalysis and electron transfer.
• Involved in the response to nitrosative stress in bacteria and fungi.
• Highlights the evolutionary diversity of globin proteins and their functions.
• Potential applications in biotechnology for NO sensing and removal.
What Happens During nitric oxide dioxygenase activity, heme protein as donor?
Substrate Binding and Heme Reduction
In simple terms: The enzyme first binds nitric oxide and oxygen, and its heme iron must be in the reduced Fe(II) state to start the reaction.
The catalytic cycle begins with the heme b cofactor in the ferrous (Fe(II)) state. Nitric oxide (NO) and molecular oxygen (O2) bind to the heme iron, forming a ternary complex. The binding of NO to ferrous heme is rapid and reversible, while O2 binding is also essential for the reaction. The precise order of binding may vary among different flavohemoglobins, but both substrates must be present for catalysis.
Oxygen Activation and Nitrate Formation
In simple terms: The bound oxygen and nitric oxide react to form nitrate, and the heme iron becomes oxidized.
Once NO and O2 are bound, the heme iron facilitates the coupling of NO with O2 to produce nitrate (NO3-). This step involves the incorporation of both oxygen atoms from O2 into nitrate, classifying the enzyme as a dioxygenase. The reaction oxidizes the heme iron to the ferric (Fe(III)) state, which must be reduced back to Fe(II) for subsequent turnovers. The mechanism is thought to proceed through a ferric-peroxynitrite intermediate or a similar species, although details may differ among enzymes.
Electron Transfer and Heme Re-reduction
In simple terms: After nitrate is released, the heme iron needs to be reduced back to its starting state by electrons from a reductase partner.
The oxidized Fe(III)-heme must be reduced to Fe(II)-heme to complete the catalytic cycle. In flavohemoglobins, this reduction is tightly coupled to a fused FAD-containing reductase domain that receives electrons from NAD(P)H. The electron transfer pathway involves ordered motions within the protein, as described by Gardner (2023). This coupling ensures efficient catalysis and prevents the accumulation of oxidized heme.
Product Release and Turnover
In simple terms: Nitrate is released from the active site, and the enzyme is ready for another round.
Nitrate, the product, is released from the active site, allowing the enzyme to bind new NO and O2 molecules. The overall reaction consumes one NO and one O2 per nitrate produced, with the heme iron cycling between Fe(II) and Fe(III) states. The turnover rate can be influenced by the availability of substrates and reducing equivalents, as well as by the specific protein environment.
Key Genes Involved in GO:0141118 nitric oxide dioxygenase activity, heme protein as donor
The following genes and proteins are directly associated with nitric oxide dioxygenase activity, heme protein as donor, based on published biochemical and genetic studies.
| Gene | Major Role | Research Relevance |
|---|---|---|
| hmp (flavohemoglobin) | Nitric oxide dioxygenase in bacteria | Model enzyme for NO detoxification; knockout increases NO sensitivity |
| fhb (flavohemoglobin) | Nitric oxide dioxygenase in Mycobacterium smegmatis | Type I flavohemoglobin with confirmed NOD activity |
| MSMEG_0710 | Type II flavohemoglobin in M. smegmatis | Oxidizes d-lactate and mediates electron transfer |
| hmpA (Acinetobacter baumannii) | Novel hemoglobin conferring NO resistance | Contributes to host-derived NO resistance |
| Yhb1 (Saccharomyces cerevisiae) | Flavohemoglobin in yeast | Protects against nitrosative stress |
| Hmp (Escherichia coli) | Flavohemoglobin | Well-studied NOD; structural and kinetic models |
| Rbt1 (Candida albicans) | Flavohemoglobin | Role in NO resistance and virulence |
| Fhp (Bacillus subtilis) | Flavohemoglobin | NO detoxification in Gram-positive bacteria |
| NOD (Mycobacterium tuberculosis) | Putative nitric oxide dioxygenase | Potential drug target for tuberculosis |
| GlbN (Synechocystis) | Truncated hemoglobin | May have NOD-like activity |
| HbN (Mycobacterium tuberculosis) | Truncated hemoglobin | NO detoxification and signaling |
| Cgb (Vitreoscilla) | Bacterial hemoglobin | Enhances NO resistance and respiration |
| Hmp (Salmonella typhimurium) | Flavohemoglobin | Required for virulence in mice |
| Fhb (Aspergillus nidulans) | Flavohemoglobin | NO detoxification in fungi |
| Hmp (Pseudomonas aeruginosa) | Flavohemoglobin | Biofilm formation and NO resistance |
| NOD (Vibrio cholerae) | Nitric oxide dioxygenase | Survival under nitrosative stress |
| Hmp (Staphylococcus aureus) | Flavohemoglobin | NO resistance and pathogenesis |
| Hmp (Listeria monocytogenes) | Flavohemoglobin | Intracellular survival |
How Is nitric oxide dioxygenase activity, heme protein as donor Regulated?
The expression and activity of nitric oxide dioxygenases are regulated at multiple levels. In many bacteria, the genes encoding flavohemoglobins are induced by nitric oxide and nitrosative stress, often through transcriptional regulators such as NsrR or Fnr. For example, in Escherichia coli, Hmp expression is upregulated in response to NO and nitrate, and its activity is also modulated by the availability of NAD(P)H and FAD. In Mycobacterium smegmatis, the type I flavohemoglobin is expressed under aerobic conditions and contributes to NO detoxification. Additionally, the catalytic cycle itself is regulated by the redox state of the heme and the efficiency of electron transfer from the reductase domain, which can be influenced by protein-protein interactions and conformational changes. Post-translational modifications and proteolytic cleavage may also affect activity, although these are less well characterized.
nitric oxide dioxygenase activity, heme protein as donor and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| hmpA (A. baumannii) | Opportunistic infections, NO resistance | Knockout in A. baumannii; infection model |
| fhb (M. smegmatis) | Mycobacterial survival, NO detoxification | Knockout in M. smegmatis; macrophage infection |
| hmp (S. typhimurium) | Virulence, intracellular survival | Mouse infection model |
| Yhb1 (C. albicans) | Fungal virulence, nitrosative stress | Knockout in C. albicans; macrophage assay |
| Hmp (P. aeruginosa) | Biofilm formation, chronic lung infection | Knockout in P. aeruginosa; biofilm model |
Bacterial Pathogenesis and Host Defense
Nitric oxide dioxygenase activity is critical for the survival of many bacterial pathogens within host organisms. For instance, Acinetobacter baumannii uses a novel hemoglobin with this activity to resist host-derived NO, contributing to its ability to cause opportunistic infections. Similarly, Mycobacterium smegmatis type I flavohemoglobin detoxifies NO, which may be important for its persistence in macrophages. In Salmonella typhimurium, the flavohemoglobin Hmp is required for full virulence in mice, highlighting the role of this activity in pathogenesis. These findings suggest that inhibitors of nitric oxide dioxygenases could serve as novel antimicrobial agents.
Inflammatory Diseases and Nitrosative Stress
Chronic inflammation leads to sustained production of nitric oxide, which can damage host tissues. Microbial enzymes with nitric oxide dioxygenase activity may modulate the inflammatory environment by removing NO, potentially affecting disease outcomes. For example, in cystic fibrosis, Pseudomonas aeruginosa expresses flavohemoglobin to survive nitrosative stress in the lungs. Understanding how this activity influences host-microbe interactions could lead to new therapeutic strategies for inflammatory diseases.
Potential Role in Cancer and Cell Signaling
Nitric oxide is a signaling molecule involved in various physiological processes, including vasodilation and neurotransmission. While direct links between GO:0141118 and cancer are not well established, the ability to modulate NO levels could influence tumor microenvironments. Some bacteria that colonize tumors may use this activity to survive, but further research is needed to clarify any role in cancer.
From nitric oxide dioxygenase activity, heme protein as donor-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| Does loss of NOD activity increase NO sensitivity? | Knockout of hmp or fhb in bacteria |
| Does a point mutation in the heme pocket alter catalysis? | Point mutation (e.g., His to Ala) in flavohemoglobin |
| Can a tagged version be used for localization? | Knock-in of FLAG or GFP tag at endogenous locus |
| Does overexpression enhance NO resistance? | Overexpression of hmp in E. coli or M. smegmatis |
| Which residues are essential for electron transfer? | Site-directed mutagenesis of reductase domain |
| Does the enzyme protect against host NO in vivo? | Knockout in pathogen; mouse infection model |
How to Study the nitric oxide dioxygenase activity, heme protein as donor Process
| Method | What It Measures | Typical Application |
|---|---|---|
| NO electrode | Real-time NO consumption | Kinetic assays of purified enzyme |
| Nitrate quantification | Nitrate production | Endpoint assays of NOD activity |
| UV-visible spectroscopy | Heme redox state | Monitoring Fe(II)/Fe(III) transitions |
| EPR spectroscopy | Paramagnetic intermediates | Detecting reaction intermediates |
| X-ray crystallography | Three-dimensional structure | Active site architecture |
| RNA-seq | Gene expression changes | Identifying NO-regulated genes |
| Knockout mutagenesis | Loss of function phenotype | Assessing NO sensitivity |
| Infection models | Virulence and survival in host | Testing role in pathogenesis |
Enzymatic Assays for Nitric Oxide Dioxygenase Activity
The most direct way to measure GO:0141118 is to monitor the consumption of NO or the production of nitrate. NO consumption can be followed using an NO-sensitive electrode or by chemiluminescence, while nitrate can be quantified by colorimetric assays or HPLC. These assays typically use purified enzyme, NAD(P)H as electron donor, and FAD for flavohemoglobins. Kinetic parameters such as kcat and Km can be determined under anaerobic or aerobic conditions.
Genetic Approaches: Knockouts and Complementation
To study the physiological role of nitric oxide dioxygenases, researchers generate knockout mutants in bacterial or fungal strains and compare their survival under nitrosative stress. For example, deletion of hmp in E. coli increases sensitivity to NO. Complementation with wild-type or mutant alleles can confirm that the observed phenotype is due to the specific gene. These experiments are often combined with infection models to assess virulence.
Structural and Spectroscopic Methods
Understanding the catalytic mechanism requires structural and spectroscopic characterization. X-ray crystallography and NMR can reveal the heme environment and conformational changes. UV-visible spectroscopy is used to monitor the redox state of the heme iron, while electron paramagnetic resonance (EPR) can detect reaction intermediates. These methods provide atomic-level insights into substrate binding and catalysis.
Transcriptomics and Proteomics
RNA-seq and proteomics can identify genes and proteins regulated by NO or involved in nitrosative stress responses. For instance, transcriptomic analysis of M. smegmatis under NO stress can reveal upregulation of fhb and other genes. Proteomic approaches can detect post-translational modifications and protein-protein interactions, such as the coupling between the heme domain and reductase domain.
How CRISPR Can Be Used to Study GO:0141118 nitric oxide dioxygenase activity, heme protein as donor
Knockout
CRISPR-Cas9 knockout of genes encoding nitric oxide dioxygenases, such as hmp or fhb, can be used to create loss-of-function mutants. These models are essential for determining whether the enzyme is required for NO resistance and virulence. For example, knocking out hmpA in Acinetobacter baumannii would test its role in host-derived NO resistance. EDITGENE provides custom knockout cell lines and bacterial strains to accelerate this research.
Point Mutation
Point mutations can be introduced into the catalytic site or electron transfer pathway to dissect the mechanism. For instance, mutating the distal histidine in flavohemoglobin may alter NO binding or oxygen activation. CRISPR-based base editing or homology-directed repair allows precise introduction of such mutations. EDITGENE offers point mutation services to generate isogenic models with specific amino acid changes.
Knock-in
Knock-in of tags (e.g., FLAG, GFP) or reporter genes at the endogenous locus enables real-time monitoring of expression and localization. This is particularly useful for studying the regulation of nitric oxide dioxygenases under different conditions. EDITGENE provides knock-in services for tagging endogenous genes in various cell types and organisms.
Overexpression
Overexpression of nitric oxide dioxygenases can enhance NO resistance and provide a gain-of-function model. For example, overexpressing hmp in E. coli increases survival under nitrosative stress. CRISPR activation (CRISPRa) or plasmid-based overexpression can achieve this. EDITGENE offers overexpression services to create stable cell lines with elevated enzyme levels.
How EDITGENE Supports nitric oxide dioxygenase activity, heme protein as donor Research
Researchers studying nitric oxide dioxygenase activity, heme protein as donor-related genes often need to determine whether a candidate gene is causally involved in NO detoxification, pathogenesis, or cellular stress responses. This requires precise genetic manipulation, which can be challenging without optimized tools. EDITGENE specializes in providing custom CRISPR-based models to address these questions efficiently.
Contact EDITGENE today to design your custom CRISPR model for nitric oxide dioxygenase activity, heme protein as donor research.
Frequently Asked Questions About nitric oxide dioxygenase activity, heme protein as donor
What is nitric oxide dioxygenase activity, heme protein as donor?
It is a molecular function (GO:0141118) that catalyzes the conversion of nitric oxide and oxygen to nitrate using a heme b-containing protein, as defined by the reaction Fe(II)-heme b-[protein] + NO + O2 = Fe(III)-heme b-[protein] + nitrate.
What genes are involved in nitric oxide dioxygenase activity, heme protein as donor?
Key genes include flavohemoglobins such as hmp in E. coli, fhb in Mycobacterium smegmatis, and hmpA in Acinetobacter baumannii, among others.
How does nitric oxide dioxygenase protect bacteria from nitric oxide?
It detoxifies NO by converting it to nitrate, preventing NO from damaging cellular components and allowing pathogens to survive host immune responses.
What is the reaction catalyzed by GO:0141118?
The reaction is: Fe(II)-heme b-[protein] + nitric oxide + O2 = Fe(III)-heme b-[protein] + nitrate.
Which organisms have nitric oxide dioxygenase activity?
Many bacteria, fungi, and some protozoa possess this activity, often through flavohemoglobins or truncated hemoglobins.
Is nitric oxide dioxygenase activity a drug target?
Yes, because it is important for pathogen survival, inhibitors could be developed as antimicrobial agents.
What is the difference between nitric oxide dioxygenase and nitric oxide reductase?
Nitric oxide dioxygenase incorporates oxygen into nitrate, while nitric oxide reductase reduces NO to N2O or other products without incorporating O2.
How can I study nitric oxide dioxygenase activity in the lab?
Common methods include measuring NO consumption with an electrode, quantifying nitrate production, and using knockout mutants to assess NO sensitivity.
What are the substrates of nitric oxide dioxygenase?
The substrates are nitric oxide (NO), molecular oxygen (O2), and reduced heme b (Fe(II)-heme b).
What diseases are associated with nitric oxide dioxygenase activity?
It is linked to bacterial infections, particularly those caused by pathogens that resist host NO, such as Acinetobacter baumannii and Mycobacterium species.
Conclusion
GO:0141118, nitric oxide dioxygenase activity, heme protein as donor, is a crucial enzymatic function that enables organisms to detoxify nitric oxide, a key antimicrobial molecule. Through the action of flavohemoglobins and related heme proteins, this activity converts NO to nitrate, supporting pathogen survival and influencing host-pathogen interactions. Understanding its mechanism, regulation, and role in disease provides opportunities for therapeutic intervention and biotechnological applications. Researchers can leverage CRISPR-based models and biochemical assays to further explore this activity and its biological significance.
References
- 1. Bonamore A et al.. 2008. Flavohemoglobin: structure and reactivity.. IUBMB Life 60(1):19-28 PMID: 18379989
- 2. Gardner PR. 2023. Ordered Motions in the Nitric-Oxide Dioxygenase Mechanism of Flavohemoglobin and Assorted Globins with Tightly Coupled Reductases.. Adv Exp Med Biol 1414:45-96 PMID: 36520413
- 3. Thakur N et al.. 2014. Type I flavohemoglobin of mycobacterium smegmatis is a functional nitric oxide dioxygenase.. IUBMB Life 66(6):396-404 PMID: 24861678
- 4. Beas JZ et al.. 2025. A novel type of hemoglobin confers host-derived nitric oxide resistance to the opportunistic pathogen Acinetobacter baumannii.. Sci Rep 15(1):5969 PMID: 39966482
- 5. Thakur N et al.. 2018. Type II flavohemoglobin of Mycobacterium smegmatis oxidizes d-lactate and mediate electron transfer.. Int J Biol Macromol 112:868-875 PMID: 29428388
