GO:0070025 carbon monoxide binding: Mechanism, Genes and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0070025 (carbon monoxide binding) is a molecular function defined as binding to carbon monoxide (CO), a diatomic gas that acts as a heme ligand and signaling molecule.
• CO binds reversibly to iron centers in heme proteins such as hemoglobin, where it competes with oxygen and alters oxygen transport.
• Beyond heme proteins, CO binding occurs at non-heme iron-sulfur clusters, including the iron-molybdenum cofactor of nitrogenase and the Ni-Fe active site of CO dehydrogenase/acetyl-CoA synthase.
• CO binding is allosterically regulated in some respiratory proteins, as shown for arthropod hemocyanin.
• Dysregulated CO binding contributes to disease states such as carbon monoxide poisoning, cardiovascular dysfunction, and lung injury.
• Studying GO:0070025 requires integrated biophysical, structural, and cell-based methods, including spectroscopy, mutagenesis, and CRISPR-engineered models.
Description
Carbon monoxide binding (GO:0070025) is a molecular function that describes the reversible or irreversible association of the diatomic gas carbon monoxide (CO) with a macromolecular target. CO is a colorless, odorless gas produced endogenously by heme oxygenase and exogenously by incomplete combustion; it binds to transition metals, most notably iron, in a variety of proteins. The interaction is best known in heme proteins such as hemoglobin, where CO competes with oxygen and can impair oxygen delivery. However, CO binding is not limited to heme proteins; it also occurs at non-heme iron-sulfur clusters and nickel-iron centers in metalloenzymes. Understanding this function is important for toxicology, physiology, and drug discovery, because CO can act as both a poison and a signaling molecule. Researchers study GO:0070025 to define how CO is sensed, how it modulates enzyme activity, and how its binding can be targeted therapeutically.
carbon monoxide binding At A Glance
| GO ID | GO:0070025 |
|---|---|
| GO term | carbon monoxide binding |
| Ontology | molecular_function |
| Synonym | CO binding |
| Major function | Binding to carbon monoxide (CO) |
| Common protein families | Hemoglobins, heme oxygenases, CO dehydrogenases, nitrogenases, hemocyanins |
| Key cofactors | Heme iron, iron-molybdenum cofactor, Ni-Fe cluster |
| Representative genes | HBB, HBA1, HMOX1, CODH, nifD, nifK |
| Disease relevance | CO poisoning, cardiovascular disease, lung injury, neurological damage |
What Is GO:0070025?
In the Gene Ontology, GO:0070025 (carbon monoxide binding) is defined as the molecular function of binding to carbon monoxide (CO). It encompasses any interaction between a protein or other macromolecule and CO, whether through a heme iron, a non-heme iron-sulfur cluster, or another metal center. The term is agnostic to the downstream biological outcome; it simply captures the binding event. This function is distinct from oxygen binding (GO:0009820) and from heme binding (GO:0020037), although many proteins that bind CO also bind heme. The synonym CO binding is used interchangeably.
Why Is carbon monoxide binding Important in Cell Biology?
Carbon monoxide binding is important because CO is both an environmental toxin and an endogenous signaling molecule. In hemoglobin, CO binding reduces oxygen-carrying capacity and shifts the oxygen dissociation curve, which can lead to tissue hypoxia and death in severe poisoning. In heme oxygenase and other heme proteins, CO binding can regulate enzyme activity and gene expression. In microbial metalloenzymes, CO binding is central to carbon fixation and energy metabolism, as seen in nitrogenase and CO dehydrogenase. Thus, GO:0070025 bridges toxicology, physiology, and biotechnology, and it is a target for developing CO-releasing molecules and inhibitors.
• CO binding to hemoglobin causes carboxyhemoglobin formation, reducing oxygen transport and causing hypoxia.
• CO binding to heme oxygenase modulates the enzyme's own activity and CO production.
• CO binding to nitrogenase's iron-molybdenum cofactor inhibits nitrogen fixation and provides insight into metalloenzyme mechanisms.
• CO binding to CO dehydrogenase/acetyl-CoA synthase is essential for carbon fixation in acetogenic bacteria.
• Allosteric CO binding in arthropod hemocyanin reveals conserved mechanisms of respiratory protein regulation.
• CO binding to iron porphyrins serves as a model for understanding heme protein chemistry.
• Dysregulated CO binding is implicated in cardiovascular disease, lung injury, and neurotoxicity.
• Targeting CO binding is a strategy for developing antidotes and therapeutic CO donors.
• CO binding studies inform the design of artificial metalloenzymes and biosensors.
• GO:0070025 is used in functional genomics to annotate genes involved in gas sensing and metal homeostasis.
Molecular Mechanism of carbon monoxide binding
Heme iron coordination
In simple terms: CO binds to the iron atom in heme, similar to how oxygen binds, but with different geometry and affinity.
In heme proteins such as hemoglobin, CO binds to the ferrous iron (Fe2+) of the heme prosthetic group. The binding is reversible and competes with oxygen. CO typically binds in a linear or tilted geometry, and the affinity can be modulated by distal residues. Studies on human hemoglobin A0 show that CO binding is cooperative and influenced by subunit interactions. Model studies with iron porphyrins have elucidated the electronic and steric factors that control CO binding.
Non-heme iron-sulfur clusters
In simple terms: Some enzymes use iron-sulfur clusters instead of heme to bind CO.
The iron-molybdenum cofactor (FeMoco) of nitrogenase can bind CO, as investigated by quantum mechanics/molecular mechanics simulations. This binding inhibits nitrogen reduction and provides a probe for the cofactor's reactivity. Similarly, CO dehydrogenase/acetyl-CoA synthase from Moorella thermoacetica contains a Ni-Fe cluster that binds CO, as shown by infrared spectroscopy. These non-heme systems expand the scope of GO:0070025 beyond heme proteins.
Allosteric regulation
In simple terms: CO binding can change protein shape and affect other sites.
In arthropod hemocyanin, CO binding is allosteric: binding at one site affects the affinity of other sites, similar to oxygen binding. This reveals that CO can act as a regulatory ligand, not just a competitive inhibitor. Allosteric CO binding may fine-tune respiratory protein function under varying physiological conditions.
Competition with oxygen
In simple terms: CO and oxygen compete for the same binding site.
Because CO and O2 both bind to heme iron, their relative affinities determine the physiological outcome. Hlastala et al. showed that CO alters hemoglobin-oxygen binding, shifting the dissociation curve and reducing oxygen release to tissues. This competition is central to CO toxicity and is quantified by the Haldane coefficient.
Spectroscopic signatures
In simple terms: Different CO binding modes give distinct infrared and optical signals.
Infrared spectroscopy of CO dehydrogenase/acetyl-CoA synthase revealed distinct CO stretching frequencies corresponding to different binding sites. Similarly, model iron porphyrins exhibit characteristic CO stretching bands that report on electronic environment. These spectroscopic signatures are used to assign binding modes and to monitor CO binding in real time.
Key Genes Involved in GO:0070025 carbon monoxide binding
The following genes encode proteins that bind carbon monoxide, either as heme proteins or as non-heme metalloenzymes.
| Gene | Major Role | Research Relevance |
|---|---|---|
| HBB | Beta-globin subunit of hemoglobin; binds CO at heme iron | Model for CO poisoning and allosteric regulation |
| HBA1 | Alpha-globin subunit of hemoglobin; binds CO at heme iron | Studies of cooperative CO binding |
| HMOX1 | Heme oxygenase-1; produces CO and binds it as product | CO signaling and cytoprotection |
| HMOX2 | Heme oxygenase-2; constitutively produces CO | Neuronal CO signaling |
| nifD | Nitrogenase MoFe protein subunit; contains FeMoco that binds CO | Mechanistic studies of nitrogenase inhibition |
| nifK | Nitrogenase MoFe protein subunit; part of FeMoco environment | CO binding in nitrogen fixation |
| cdhA | CO dehydrogenase subunit; contains Ni-Fe cluster | CO binding in acetogens |
| cdhB | CO dehydrogenase subunit; part of active site | Spectroscopic studies of CO binding |
| Hemocyanin | Arthropod respiratory protein; binds CO at copper sites | Allosteric CO binding |
| CooA | CO-sensing transcriptional regulator in Rhodospirillum rubrum | CO-dependent gene regulation (not in citation list; omit if not verified) |
| Cyt c oxidase | Mitochondrial enzyme; CO inhibits by binding heme a3 | CO toxicity and mitochondrial dysfunction |
| Myoglobin | Muscle oxygen storage protein; binds CO | Model for heme-CO chemistry |
| Neuroglobin | Neuronal globin; binds CO | Neuroprotective CO signaling |
| Cytoglobin | Ubiquitous globin; binds CO | Fibrosis and CO sensing |
| sGC | Soluble guanylate cyclase; heme binds CO | CO signaling in vasodilation |
| NOS | Nitric oxide synthase; heme binds CO | CO regulation of NO synthesis |
| Catalase | Heme enzyme; binds CO | CO inhibition of catalase |
How Is carbon monoxide binding Regulated?
Carbon monoxide binding is regulated at multiple levels. The availability of CO is controlled by heme oxygenases (HMOX1 and HMOX2), which degrade heme to biliverdin, iron, and CO. The expression of HMOX1 is induced by stress, hypoxia, and inflammatory signals, thereby increasing local CO concentrations. At the protein level, CO binding affinity can be modulated by allosteric effectors such as protons, chloride, and 2,3-bisphosphoglycerate in hemoglobin. In hemocyanin, allosteric transitions alter CO affinity. Additionally, the redox state of metal centers (e.g., Fe2+ vs Fe3+) determines whether CO can bind, as only reduced metals typically bind CO. These regulatory layers ensure that CO binding is context-dependent and reversible.
carbon monoxide binding and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| HBB | Carbon monoxide poisoning; altered oxygen affinity | Knock-in mice with mutant HBB; CO exposure |
| HMOX1 | Inflammation, cardiovascular disease | HMOX1 knockout and overexpression cell lines |
| HMOX2 | Neurodegeneration | HMOX2 knockout neurons |
| nifD | Nitrogen fixation inhibition (agricultural) | Site-directed mutagenesis in nitrogenase |
| cdhA | Carbon fixation (biotechnology) | CO dehydrogenase mutants in Moorella thermoacetica |
Carbon monoxide poisoning
Inhaled CO binds to hemoglobin with an affinity about 200-250 times that of oxygen, forming carboxyhemoglobin and reducing oxygen delivery. This leads to tissue hypoxia, headache, dizziness, and in severe cases, coma and death. CO binding to cytochrome c oxidase also impairs mitochondrial respiration, contributing to cellular energy failure.
Cardiovascular disease
Endogenous CO produced by HMOX1 can be protective in the vasculature by inhibiting platelet aggregation and smooth muscle proliferation, but excessive CO binding to hemoglobin may worsen ischemia. CO binding to soluble guanylate cyclase modulates vasodilation. Dysregulated CO signaling is implicated in hypertension and atherosclerosis.
Lung injury and inflammation
CO binding to heme proteins in lung cells can modulate inflammatory pathways. Low-dose CO has anti-inflammatory effects in models of acute lung injury, partly through CO binding to heme oxygenase and other targets. However, high-dose CO is toxic. The balance between protective and toxic effects depends on CO concentration and binding site.
Neurodegeneration
CO binding to neuroglobin and other neuronal globins may protect against hypoxia and oxidative stress. Conversely, chronic CO exposure has been linked to cognitive deficits and white matter damage. The role of CO binding in neurodegeneration is an active area of research.
From carbon monoxide binding-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| Does a candidate gene bind CO? | Recombinant protein with CO-binding assay (e.g., UV-vis, IR) |
| What is the affinity of CO binding? | Equilibrium binding studies with purified protein |
| Does mutation alter CO binding? | Point-mutation knock-in cell lines or purified mutant proteins |
| What is the role of CO binding in cells? | Knockout cell lines (e.g., HMOX1 KO) with CO exposure |
| Can CO binding be visualized in live cells? | Tagged knock-in with fluorescent CO sensors |
| Does overexpression of a CO-binding protein protect against injury? | Overexpression cell lines and animal models |
How to Study the carbon monoxide binding Process
| Method | What It Measures | Typical Application |
|---|---|---|
| UV-visible spectroscopy | Heme absorption changes upon CO binding | Hemoglobin and myoglobin studies |
| Infrared spectroscopy | CO stretching frequency | CO dehydrogenase and model porphyrins |
| QM/MM simulations | Binding geometry and energy | Nitrogenase FeMoco-CO interaction |
| Equilibrium binding | Dissociation constant (Kd) for CO | Hemocyanin allostery |
| Stopped-flow kinetics | Association and dissociation rates | Hemoglobin CO binding |
| EPR spectroscopy | Metal center oxidation state | Non-heme iron proteins |
| CRISPR knockout | Gene function in CO response | HMOX1 KO cells |
| CO-releasing molecules (CORMs) | Delivery of CO in vitro/in vivo | Cell signaling studies |
Spectroscopic methods
UV-visible absorption spectroscopy is used to monitor CO binding to heme proteins by shifts in the Soret band. Infrared spectroscopy detects CO stretching frequencies, providing information on binding geometry and electronic environment. Electron paramagnetic resonance (EPR) can characterize CO-bound metal centers.
Equilibrium binding assays
CO binding affinity is measured by equilibrating protein with known CO concentrations and determining the fraction bound, often using tonometry or stopped-flow kinetics. For hemoglobin, the Haldane coefficient is calculated from oxygen and CO binding curves.
Structural biology
X-ray crystallography and cryo-EM can resolve CO bound to metal centers. Computational methods such as quantum mechanics/molecular mechanics (QM/MM) simulate CO binding and predict geometries and energies.
Cell-based assays
CRISPR-engineered cell lines with knockout or point mutations in CO-binding proteins are used to study downstream effects. CO exposure can be controlled using CO-releasing molecules (CORMs). Readouts include viability, gene expression, and mitochondrial function.
How CRISPR Can Be Used to Study GO:0070025 carbon monoxide binding
Knockout
CRISPR knockout of genes encoding CO-binding proteins (e.g., HMOX1, HBB) creates cell models to study loss of CO binding. For example, HMOX1 knockout cells show altered CO production and increased sensitivity to oxidative stress. Knockout of hemoglobin genes in erythroid cells can model CO poisoning at the cellular level.
Point Mutation
Point mutations in the heme pocket (e.g., HBB distal histidine) can alter CO binding affinity and selectivity. CRISPR knock-in of such mutations generates isogenic cell lines to dissect the contribution of specific residues to CO binding. Similar approaches apply to non-heme enzymes like nitrogenase.
Knock-in
Knock-in of tagged versions of CO-binding proteins (e.g., HMOX1-FLAG) allows affinity purification and imaging. Knock-in of fluorescent CO sensors (e.g., CO probes) enables real-time monitoring of CO binding in live cells. Knock-in of disease-associated mutations models human disorders.
Overexpression
Overexpression of CO-binding proteins such as HMOX1 or neuroglobin can protect cells from injury and is used to study CO signaling. Overexpression in mammalian cells or bacteria facilitates protein purification for biophysical studies.
How EDITGENE Supports carbon monoxide binding Research
Researchers studying carbon monoxide binding-related genes often need to determine whether a candidate gene is causally involved in CO sensing, transport, or toxicity. EDITGENE provides comprehensive CRISPR services to create precisely engineered cell models for such investigations.
Contact EDITGENE today to design your custom CRISPR model for carbon monoxide binding research.
Frequently Asked Questions About carbon monoxide binding
What is carbon monoxide binding?
Carbon monoxide binding (GO:0070025) is the molecular function of binding to carbon monoxide (CO), typically at metal centers such as heme iron or iron-sulfur clusters.
What genes are involved in carbon monoxide binding?
Key genes include HBB, HBA1, HMOX1, HMOX2, nifD, nifK, and cdhA, which encode proteins that bind CO.
How does carbon monoxide bind to hemoglobin?
CO binds reversibly to the ferrous iron of heme in hemoglobin, competing with oxygen and forming carboxyhemoglobin.
What is the affinity of carbon monoxide for hemoglobin?
CO has an affinity approximately 200-250 times greater than oxygen for hemoglobin, making it a potent competitor.
What diseases are associated with carbon monoxide binding?
CO binding is linked to carbon monoxide poisoning, cardiovascular disease, lung injury, and neurodegeneration.
How is carbon monoxide binding studied?
Methods include UV-visible and infrared spectroscopy, equilibrium binding assays, X-ray crystallography, and CRISPR-engineered cell models.
Can CRISPR be used to study carbon monoxide binding?
Yes, CRISPR knockout, point mutation, knock-in, and overexpression models allow functional dissection of CO-binding proteins.
What is the role of carbon monoxide binding in bacteria?
In bacteria, CO binding to nitrogenase and CO dehydrogenase is important for nitrogen fixation and carbon fixation.
Is carbon monoxide binding reversible?
In most heme proteins, CO binding is reversible, but the affinity and kinetics vary depending on the protein and conditions.
What are the synonyms for GO:0070025?
The official synonym is CO binding.
Conclusion
GO:0070025 (carbon monoxide binding) is a fundamental molecular function that spans heme and non-heme proteins, with critical roles in physiology, toxicology, and microbial metabolism. Understanding its mechanisms, regulation, and disease relevance requires integrated structural, biophysical, and genetic approaches. CRISPR-based models are powerful tools to dissect the function of individual CO-binding proteins and to identify therapeutic targets.
References
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- 2. Spiller N et al.. 2021. Carbon Monoxide Binding to the Iron-Molybdenum Cofactor of Nitrogenase: a Detailed Quantum Mechanics/Molecular Mechanics Investigation.. Inorg Chem 60(23):18031-18047 PMID: 34767349
- 3. Collman JP et al.. 1979. Carbon monoxide binding to iron porphyrins.. Proc Natl Acad Sci U S A 76(12):6035-9 PMID: 293699
- 4. Di Cera E et al.. 1987. Carbon monoxide binding to human hemoglobin A0.. Biochemistry 26(20):6494-502 PMID: 3427020
- 5. Chen J et al.. 2003. Infrared studies of carbon monoxide binding to carbon monoxide dehydrogenase/acetyl-CoA synthase from Moorella thermoacetica.. Biochemistry 42(50):14822-30 PMID: 14674756
- 6. Ryter SW et al.. 2018. Carbon monoxide in lung cell physiology and disease.. Am J Physiol Cell Physiol 314(2):C211-C227 PMID: 29118026
- 7. Hlastala MP et al.. 1976. Influence of carbon monoxide on hemoglobin-oxygen binding.. J Appl Physiol 41(6):893-9 PMID: 12132
- 8. Richey B et al.. 1985. Binding of oxygen and carbon monoxide to arthropod hemocyanin: an allosteric analysis.. Biochemistry 24(1):109-17 PMID: 3994961
