GO:0120501 F-actin monooxygenase activity: Mechanism, Genes and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0120501 F-actin monooxygenase activity is a molecular function that catalyzes the oxidation of L-methionyl residues in F-actin to L-methionyl-(R)-S-oxide, using NADPH, O2, and H+.
• This activity is primarily carried out by MICAL family enzymes (MICAL1, MICAL2, MICAL3), which are flavin-dependent monooxygenases that directly modify actin filaments [1,4].
• MICAL-mediated actin oxidation leads to filament disassembly, affecting processes such as cytokinesis, HIV-1 budding, endosomal fission, and ciliogenesis [3,5,6,8].
• MICAL enzymes are tightly regulated by autoinhibition and relief mechanisms, including PAK1-mediated phosphorylation and interactions with other proteins [1,4,7].
• Dysregulation of F-actin monooxygenase activity is implicated in cancer, neurological disorders, and infectious diseases, making it a potential therapeutic target [2,3,6].
• Studying this activity requires advanced methods such as CRISPR knockout, point mutation, live-cell imaging, and biochemical assays to dissect its roles in health and disease.
Description
F-actin monooxygenase activity (GO:0120501) is a molecular function that catalyzes the oxidation of specific methionine residues in actin filaments, converting L-methionyl-[F-actin] to L-methionyl-(R)-S-oxide-[F-actin] in a reaction that consumes NADPH, O2, and H+. This post-translational modification directly alters actin dynamics and is emerging as a critical regulatory mechanism in diverse cellular processes. The primary enzymes responsible for this activity are the MICAL (Molecule Interacting with CasL) family of oxidoreductases, which include MICAL1, MICAL2, and MICAL3 [1,4]. These enzymes are conserved from flies to humans and play key roles in cytoskeletal reorganization during development, immune responses, and disease [3,6,8]. Researchers are increasingly interested in F-actin monooxygenase activity because it provides a direct link between redox signaling and actin cytoskeleton remodeling, a process fundamental to cell shape, motility, division, and vesicle trafficking [3,5,6,8]. Understanding its mechanism and regulation offers insights into basic cell biology and potential therapeutic strategies for cancer, infectious diseases, and neurological disorders [2,3,6].
F-actin monooxygenase activity At A Glance
| GO ID | GO:0120501 |
|---|---|
| GO term | F-actin monooxygenase activity |
| Ontology | molecular_function |
| Synonym | None |
| Definition | Catalysis of the reaction: L-methionyl-[F-actin] + NADPH + O2 + H+ = L-methionyl-(R)-S-oxide-[F-actin] + NADP+ + H2O. |
| Major function | Oxidation of methionine residues in F-actin, leading to actin filament disassembly. |
| Cofactors | NADPH, FAD (flavin adenine dinucleotide), molecular oxygen (O2). |
| Localization | Cytoplasm, associated with actin filaments and cellular membranes. |
| Representative enzymes | MICAL1, MICAL2, MICAL3 (flavin-dependent monooxygenases). |
What Is GO:0120501?
F-actin monooxygenase activity is defined as the catalysis of the reaction: L-methionyl-[F-actin] + NADPH + O2 + H+ = L-methionyl-(R)-S-oxide-[F-actin] + NADP+ + H2O. In simpler terms, it is an enzymatic activity that adds an oxygen atom to methionine residues within actin filaments, using NADPH as an electron donor and molecular oxygen as a substrate, resulting in the formation of methionine sulfoxide specifically in the R configuration. This modification occurs on actin filaments (F-actin) and is distinct from other actin modifications because it directly oxidizes methionine, leading to structural changes that promote filament disassembly.
Why Is F-actin monooxygenase activity Important in Cell Biology?
F-actin monooxygenase activity is important because it provides a direct mechanism for redox regulation of the actin cytoskeleton, influencing fundamental cellular processes such as cell division, migration, endocytosis, and viral budding [3,5,6,8]. Dysregulation of this activity has been linked to various human diseases, including cancer, where MICAL proteins can promote tumor cell invasion, and neurological disorders, where actin dynamics are critical for synaptic function [2,6]. Moreover, the unique chemistry of methionine oxidation on actin offers a target for therapeutic intervention, as inhibiting or modulating MICAL enzymes could alter disease progression [2,3].
• Regulates actin filament disassembly, which is essential for cytokinesis and cell division.
• Facilitates HIV-1 budding by promoting cortical actin disassembly.
• Controls endosomal actin dynamics and fission, impacting vesicle trafficking.
• Involved in ciliogenesis through coordination with vesicle transport proteins.
• MICAL1 activation by PAK1 links signaling pathways to actin remodeling.
• Autoinhibition and relief mechanisms ensure tight spatial and temporal control [1,4].
• Implicated in cancer progression, including bone destruction in arthritis models.
• Potential target for anti-viral and anti-cancer therapies [2,3].
• Provides a model for studying redox-dependent post-translational modifications.
• Essential for developmental processes such as axon guidance and immune cell function [4,7].
Core Mechanisms of F-actin Monooxygenase Activity
Substrate Recognition and Binding
In simple terms: The enzyme first grabs onto the actin filament and finds the specific methionine it needs to modify.
MICAL enzymes contain a flavin adenine dinucleotide (FAD)-binding domain and a calponin homology (CH) domain that mediates binding to F-actin [1,4]. Structural studies reveal that the CH domain interacts with actin filaments, positioning the catalytic domain near methionine residues, particularly Met44 and Met47 on actin. This binding is essential for subsequent oxidation and is regulated by autoinhibitory interactions within the enzyme [1,4].
Catalytic Oxidation of Methionine
In simple terms: Using oxygen and NADPH, the enzyme adds an oxygen atom to methionine, changing its chemical properties.
The monooxygenase reaction proceeds via a flavin hydroperoxide intermediate that transfers an oxygen atom to the sulfur of methionine, forming methionine (R)-sulfoxide. This reaction requires NADPH as an electron donor and molecular oxygen as the oxygen source. The oxidation is stereospecific, producing the (R)-S-oxide configuration, which alters actin structure and promotes filament disassembly.
Actin Filament Disassembly
In simple terms: Once oxidized, the actin filament becomes unstable and breaks apart.
Oxidation of methionine residues in actin induces conformational changes that destabilize the filament, leading to disassembly [4,8]. This disassembly is critical for processes such as cytokinesis, where actin filaments must be remodeled for cell separation. MICAL-mediated oxidation directly severs filaments and promotes depolymerization, a mechanism distinct from other actin-binding proteins.
Autoinhibition and Relief
In simple terms: The enzyme has a built-in brake that prevents it from working until the right signal comes along.
MICAL enzymes are autoinhibited by intramolecular interactions between their CH and catalytic domains [1,4]. Relief of autoinhibition occurs through phosphorylation by PAK1 or binding to other proteins, which induces conformational changes that expose the catalytic site [1,7]. This regulatory mechanism ensures that F-actin monooxygenase activity is spatially and temporally controlled [1,4].
Cofactors and Redox Regulation
In simple terms: The enzyme needs helper molecules like FAD and NADPH to work, and its activity is sensitive to the cell's redox state.
FAD is a tightly bound cofactor essential for catalysis, while NADPH provides reducing equivalents. The reaction consumes H+ and produces NADP+ and water. Redox conditions within the cell can influence enzyme activity, and MICALs may be modulated by oxidative stress. This links F-actin monooxygenase activity to cellular metabolism and stress responses.
Key Genes Involved in GO:0120501 F-actin monooxygenase activity
The following genes encode proteins that either directly catalyze F-actin monooxygenase activity or regulate it, based on published literature.
| Gene | Major Role | Research Relevance |
|---|---|---|
| MICAL1 | F-actin monooxygenase that oxidizes actin methionine residues | Key enzyme in cytokinesis, HIV-1 budding, and actin disassembly [3,8] |
| MICAL2 | F-actin monooxygenase involved in endosomal actin dynamics | Regulates endosomal fission and trafficking |
| MICAL3 | F-actin monooxygenase implicated in ciliogenesis and vesicle transport | Coordinates actin remodeling with vesicle transport |
| PAK1 | Serine/threonine kinase that phosphorylates and activates MICAL1 | Links signaling pathways to actin disassembly |
| TBC1D20 | RabGAP protein that coordinates vesicle transport and actin remodeling | Regulates ciliogenesis through MICAL-related pathways |
| NRF2 | Transcription factor regulating antioxidant response | Modulates oxidative stress pathways that may impact MICAL activity |
| HO-1 | Heme oxygenase-1, antioxidant enzyme | Protects against oxidative stress, potentially influencing MICAL function |
| NQO1 | NAD(P)H quinone dehydrogenase 1, antioxidant enzyme | Part of NRF2 pathway that may crosstalk with MICAL activity |
| ACTB | Beta-actin, a substrate for MICAL oxidation | Methionine oxidation alters actin dynamics [1,4] |
| ACTG1 | Gamma-actin, another actin isoform | Potential substrate for MICAL-mediated oxidation |
| CASL | Protein interacting with MICAL, involved in cytoskeletal regulation | May modulate MICAL localization and activity |
| CRMP2 | Collapsin response mediator protein 2, binds to MICAL | Regulates MICAL autoinhibition and actin dynamics |
| Rab8 | Small GTPase involved in vesicle trafficking | Cooperates with MICAL3 in ciliogenesis |
| Rab10 | Small GTPase regulating endosomal trafficking | May coordinate with MICAL2 in endosomal actin dynamics |
| Rab35 | Small GTPase involved in cytokinesis | Potential crosstalk with MICAL1 during cytokinesis |
| FLNA | Filamin A, actin-crosslinking protein | May compete with or modulate MICAL-mediated disassembly |
| Cofilin | Actin depolymerizing factor | Cooperates with MICALs in actin filament turnover |
How Is F-actin monooxygenase activity Regulated?
F-actin monooxygenase activity is regulated at multiple levels. MICAL enzymes are autoinhibited by intramolecular interactions, which are relieved by phosphorylation (e.g., by PAK1) or binding to partner proteins such as CRMP2 [1,4,7]. Additionally, redox conditions and the availability of NADPH and FAD influence catalytic activity. The NRF2/HO-1/NQO1 pathway, which controls antioxidant responses, may indirectly modulate MICAL activity by altering cellular redox state. Spatial regulation is achieved through targeting to specific cellular compartments, such as the cleavage furrow during cytokinesis or endosomal membranes [6,8].
F-actin monooxygenase activity and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| MICAL1 | HIV-1 budding, cytokinesis defects | MICAL1 knockout cells, HIV-1 infection assays [3,8] |
| MICAL2 | Endosomal trafficking disorders, cancer | MICAL2 knockout or overexpression in cancer cell lines |
| MICAL3 | Ciliopathies, developmental defects | MICAL3 knockout zebrafish or mouse models |
| PAK1 | Neurological disorders, cancer | PAK1 point mutations or inhibitors in neuronal cells |
| NRF2 | Oxidative stress-related diseases, arthritis | NRF2 knockout mice, arthritis models |
Cancer and Bone Destruction
MICAL proteins and F-actin monooxygenase activity have been implicated in cancer progression and bone destruction. A sinomenine derivative alleviates bone destruction in collagen-induced arthritis mice by suppressing mitochondrial dysfunction and oxidative stress via the NRF2/HO-1/NQO1 signaling pathway, which may intersect with MICAL-mediated actin oxidation. Dysregulated actin dynamics contribute to tumor cell invasion and metastasis, making MICAL enzymes potential therapeutic targets.
Infectious Diseases: HIV-1 Budding
HIV-1 budding requires cortical actin disassembly by the oxidoreductase MICAL1. The virus hijacks MICAL1 to remodel actin at the plasma membrane, facilitating the release of viral particles. This highlights F-actin monooxygenase activity as a host factor that could be targeted for antiviral therapy.
Neurological Disorders
MICAL enzymes are critical for axon guidance and synaptic plasticity, processes that depend on actin remodeling [4,7]. Dysregulation of MICAL-mediated actin oxidation has been linked to neurological disorders, although specific disease mechanisms are still under investigation. PAK1-mediated activation of MICAL1 suggests a role in signaling pathways relevant to neurodevelopment.
Ciliopathies and Vesicle Trafficking Disorders
TBC1D20 coordinates vesicle transport and actin remodeling to regulate ciliogenesis, a process that may involve MICAL3. Defects in ciliogenesis are associated with ciliopathies, a group of genetic disorders affecting multiple organs. MICAL2 regulates endosomal actin attenuation and fission, impacting vesicle trafficking pathways that are essential for cellular homeostasis.
From F-actin monooxygenase activity-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| Does MICAL1 knockout affect cytokinesis? | MICAL1 knockout HeLa cells |
| How does MICAL2 regulate endosomal fission? | MICAL2 knockout or overexpression in HeLa cells |
| What is the role of MICAL3 in ciliogenesis? | MICAL3 knockout RPE1 cells or zebrafish |
| Does PAK1 phosphorylation activate MICAL1? | PAK1 point mutations or inhibitors in cell lines |
| Can MICAL1 be targeted to inhibit HIV-1 budding? | MICAL1 knockout or knockdown in HIV-1 infected cells |
| Does NRF2 pathway modulate MICAL activity? | NRF2 knockout or activator treatment in arthritis models |
How to Study the F-actin monooxygenase activity Process
| Method | What It Measures | Typical Application |
|---|---|---|
| NADPH consumption assay | Monooxygenase catalytic activity | In vitro enzyme kinetics |
| Mass spectrometry | Methionine sulfoxide formation on actin | Substrate identification and quantification |
| Live-cell imaging | Actin filament disassembly dynamics | Cytokinesis, endocytosis, viral budding [6,8] |
| CRISPR knockout screens | Genes required for MICAL-mediated processes | HIV-1 budding, cytokinesis |
| Phosphorylation assays | PAK1-mediated MICAL activation | Signal transduction studies |
| Redox proteomics | Global methionine oxidation | Oxidative stress response |
| Structural biology (cryo-EM) | MICAL autoinhibition and actin binding | Mechanistic studies [1,4] |
| Ciliogenesis assays | Cilia formation and actin remodeling | Ciliopathy research |
Biochemical Assays for Monooxygenase Activity
F-actin monooxygenase activity can be measured using in vitro assays that monitor NADPH consumption or methionine sulfoxide formation. Recombinant MICAL proteins are incubated with F-actin, NADPH, and O2, and the reaction is quantified by HPLC or mass spectrometry. These assays are essential for determining kinetic parameters and testing inhibitors.
Live-Cell Imaging of Actin Dynamics
Fluorescence microscopy with actin probes (e.g., Lifeact-GFP) allows real-time visualization of actin filament disassembly upon MICAL activation. This method reveals spatial and temporal dynamics in processes like cytokinesis and endocytosis [6,8]. Photoactivatable or optogenetic tools can be used to control MICAL activity locally.
CRISPR-Based Genetic Screens
Genome-wide CRISPR knockout screens can identify genes that modulate F-actin monooxygenase activity or its downstream effects. For example, screens for HIV-1 budding factors have identified MICAL1 as essential. These screens provide unbiased insights into pathways regulating actin oxidation.
Proteomics and Redox Proteomics
Mass spectrometry-based proteomics can detect methionine oxidation on actin and other proteins, providing a global view of MICAL substrates. Redox proteomics specifically identifies oxidized methionine residues, linking F-actin monooxygenase activity to cellular redox networks [1,4].
How CRISPR Can Be Used to Study GO:0120501 F-actin monooxygenase activity
Knockout
CRISPR knockout of MICAL genes (e.g., MICAL1, MICAL2, MICAL3) in cell lines such as HeLa or RPE1 allows researchers to study loss-of-function phenotypes, including defects in cytokinesis, endosomal trafficking, and ciliogenesis [3,5,6,8]. Knockout models are essential for validating the role of F-actin monooxygenase activity in specific cellular processes.
Point Mutation
Introducing point mutations in the catalytic domain of MICAL enzymes (e.g., disrupting FAD binding or CH domain interactions) can dissect the enzymatic activity from scaffolding functions. Such mutants help identify residues critical for monooxygenase activity and autoinhibition [1,4].
Knock-in
Knock-in of tagged MICAL alleles (e.g., GFP or HA tags) enables endogenous protein localization and interaction studies. Tagged knock-in models are valuable for live-cell imaging and proteomic analyses without overexpression artifacts [1,6].
Overexpression
Overexpression of wild-type or constitutively active MICAL mutants in cells can amplify F-actin monooxygenase activity, leading to enhanced actin disassembly. This approach is useful for studying downstream effects and identifying suppressors [4,7].
How EDITGENE Supports F-actin monooxygenase activity Research
Researchers studying F-actin monooxygenase activity-related genes often need to determine whether a candidate gene is causally involved in actin remodeling, disease progression, or cellular stress responses. Precise genetic models are essential to dissect the molecular mechanisms and validate therapeutic targets.
Contact EDITGENE today to design your custom CRISPR model for F-actin monooxygenase activity research.
Frequently Asked Questions About F-actin monooxygenase activity
What is F-actin monooxygenase activity?
F-actin monooxygenase activity (GO:0120501) is a molecular function that catalyzes the oxidation of methionine residues in actin filaments, using NADPH and oxygen to produce methionine (R)-sulfoxide, leading to actin disassembly.
What genes are involved in F-actin monooxygenase activity?
The primary genes are MICAL1, MICAL2, and MICAL3, which encode flavin-dependent monooxygenases that directly oxidize actin [1,4]. Regulatory genes include PAK1, TBC1D20, and NRF2 [2,5,7].
How does MICAL1 regulate actin dynamics?
MICAL1 oxidizes methionine residues on actin, causing filament disassembly. Its activity is autoinhibited and relieved by PAK1 phosphorylation or binding to CRMP2 [1,4,7].
What diseases are associated with F-actin monooxygenase activity?
Dysregulation is linked to cancer, HIV-1 budding, neurological disorders, and ciliopathies [2,3,4,5].
What is the role of MICAL2 in endosomal trafficking?
MICAL2 regulates endosomal actin attenuation and fission, impacting vesicle trafficking and endosomal dynamics.
How can I study F-actin monooxygenase activity in the lab?
Use biochemical assays for NADPH consumption, live-cell imaging of actin, CRISPR knockout models, and proteomics to detect methionine oxidation [1,3,6].
What are the substrates of F-actin monooxygenase?
The substrate is L-methionyl-[F-actin], specifically methionine residues Met44 and Met47 on actin [1,4].
Is F-actin monooxygenase activity conserved across species?
Yes, MICAL enzymes are conserved from Drosophila to humans and play similar roles in actin regulation.
What cofactors are required for F-actin monooxygenase activity?
The reaction requires FAD as a cofactor, NADPH as an electron donor, and molecular oxygen.
How is F-actin monooxygenase activity regulated?
It is regulated by autoinhibition, phosphorylation (e.g., by PAK1), and interactions with partner proteins like CRMP2 [1,4,7].
Conclusion
F-actin monooxygenase activity (GO:0120501) is a unique enzymatic function that directly links redox chemistry to actin cytoskeleton dynamics. Through the oxidation of methionine residues on actin, MICAL family enzymes control critical processes such as cytokinesis, vesicle trafficking, viral budding, and ciliogenesis [3,5,6,8]. Dysregulation of this activity contributes to cancer, infectious diseases, and neurological disorders, making it an attractive target for therapeutic intervention [2,3,4]. Continued research using advanced CRISPR models and biochemical assays will further elucidate its mechanisms and potential clinical applications.
References
- 1. Horvath M et al.. 2024. Structural basis of MICAL autoinhibition.. Nat Commun 15(1):9810 PMID: 39532862
- 2. Guo WY et al.. 2025. A sinomenine derivative alleviates bone destruction in collagen-induced arthritis mice by suppressing mitochondrial dysfunction and oxidative stress via the NRF2/HO-1/NQO1 signaling pathway.. Pharmacol Res 215:107686 PMID: 40088961
- 3. Serrano T et al.. 2024. HIV-1 budding requires cortical actin disassembly by the oxidoreductase MICAL1.. Proc Natl Acad Sci U S A 121(48):e2407835121 PMID: 39556735
- 4. Lin L et al.. 2024. Autoinhibition and relief mechanisms for MICAL monooxygenases in F-actin disassembly.. Nat Commun 15(1):6824 PMID: 39122694
- 5. Zhai D et al.. 2025. TBC1D20 coordinates vesicle transport and actin remodeling to regulate ciliogenesis.. J Cell Biol 224(4) PMID: 39868814
- 6. Murakonda AB et al.. 2026. Endosomal actin attenuation and fission are regulated by MICAL2.. J Cell Sci 139(6) PMID: 41797580
- 7. McGarry DJ et al.. 2022. MICAL1 activation by PAK1 mediates actin filament disassembly.. Cell Rep 41(1):111442 PMID: 36198272
- 8. Frémont S et al.. 2017. Oxidation of F-actin controls the terminal steps of cytokinesis.. Nat Commun 8:14528 PMID: 28230050
