GO:0004485 methylcrotonoyl-CoA carboxylase activity: Mechanism, Genes and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0004485 methylcrotonoyl-CoA carboxylase activity catalyzes the ATP-dependent carboxylation of 3-methylbut-2-enoyl-CoA to trans-3-methylglutaconyl-CoA, a committed step in leucine catabolism.
• The enzyme is a biotin-dependent carboxylase that uses bicarbonate as the carbon source and couples ATP hydrolysis to carboxyl transfer via a biotin carrier domain.
• Human methylcrotonoyl-CoA carboxylase is a dodecameric holoenzyme composed of MCCC1 (biotin-containing alpha subunit) and MCCC2 (beta subunit).
• MCCC1 has been linked to innate immune signaling through MAVS, expanding its functional repertoire beyond metabolism.
• MCCC2 is regulated by SIRT4-mediated deacetylation and contributes to acetyl-CoA homeostasis, stemness, and invasiveness in hepatocellular carcinoma.
• Loss of the mitochondrial transporter SLC25A21 perturbs MCCC-related metabolism and promotes ferroptosis via GPX4 deficiency in colorectal cancer.
Description
Methylcrotonoyl-CoA carboxylase activity (GO:0004485) is a molecular function defined as the catalysis of the reaction: 3-methylbut-2-enoyl-CoA + ATP + bicarbonate = trans-3-methylglutaconyl-CoA + ADP + 2 H+ + phosphate. This activity is a biotin-dependent carboxylation that commits leucine-derived carbon to the 3-methylglutaconyl-CoA pathway and is essential for normal leucine catabolism. The enzyme belongs to the family of biotin-dependent carboxylases, which share a conserved biotin carboxylase domain, a biotin carboxyl carrier protein (BCCP) domain, and a carboxyltransferase domain. In humans, the activity is carried out by a heteromeric holoenzyme comprising MCCC1 and MCCC2 subunits, and structural studies have revealed how these subunits assemble into a functional dodecamer. Beyond its canonical metabolic role, methylcrotonoyl-CoA carboxylase activity has emerged as a node connecting mitochondrial metabolism to immune signaling and cancer biology. Researchers study this activity to understand inborn errors of leucine metabolism, mitochondrial substrate flux, and the metabolic rewiring of tumors.
methylcrotonoyl-CoA carboxylase activity At A Glance
| GO ID | GO:0004485 |
|---|---|
| GO term | methylcrotonoyl-CoA carboxylase activity |
| Ontology | molecular_function |
| Synonym | beta-methylcrotonyl-CoA carboxylase activity; MCCC activity; methylcrotonyl-CoA carboxylase activity |
| Major function | ATP- and biotin-dependent carboxylation of 3-methylbut-2-enoyl-CoA to trans-3-methylglutaconyl-CoA |
| Reaction | 3-methylbut-2-enoyl-CoA + ATP + bicarbonate = trans-3-methylglutaconyl-CoA + ADP + 2 H+ + phosphate |
| Cofactor | Biotin (covalently attached to the BCCP domain) |
| Subunit composition | MCCC1 (biotin-containing subunit) and MCCC2 (beta subunit) form a dodecameric holoenzyme |
| Pathway context | Leucine catabolism; mitochondrial branched-chain amino acid degradation |
What Is GO:0004485?
In practical terms, GO:0004485 describes the enzymatic activity that attaches a carboxyl group to 3-methylbut-2-enoyl-CoA using energy from ATP and bicarbonate, producing trans-3-methylglutaconyl-CoA, ADP, phosphate, and protons. The reaction is biotin-dependent: the enzyme first carboxylates its covalently bound biotin cofactor in an ATP-consuming step, then transfers the carboxyl group to the substrate. This activity is synonymous with beta-methylcrotonyl-CoA carboxylase activity and MCCC activity, and it is a required step in the leucine degradation pathway.
Why Is methylcrotonoyl-CoA carboxylase activity Important in Cell Biology?
Methylcrotonoyl-CoA carboxylase activity is important because it controls a committed step in leucine catabolism and because its subunits have been implicated in immune signaling and cancer metabolism. Deficiencies in this activity cause 3-methylcrotonyl-CoA carboxylase deficiency, an inborn error of leucine metabolism, and the enzyme is a target of newborn screening programs. Recent work shows that MCCC1 potentiates RLR-induced NF-κB signaling by targeting the MAVS complex, linking the enzyme to antiviral innate immunity. In hepatocellular carcinoma, MCCC2 deacetylation by SIRT4 controls acetyl-CoA synthesis and promotes stemness and invasiveness. In colorectal cancer, loss of SLC25A21 induces mitochondrial GPX4 deficiency and ferroptosis, a process connected to MCCC-related metabolism. Thus, GO:0004485 is relevant to metabolic disease, immunology, and oncology.
• Catalyzes a committed step in leucine catabolism, linking branched-chain amino acid breakdown to mitochondrial energy metabolism.
• Deficiency of this activity causes 3-methylcrotonyl-CoA carboxylase deficiency, an inborn error of leucine metabolism.
• MCCC1 potentiates RLR-induced NF-κB signaling by targeting the MAVS complex, connecting the enzyme to innate antiviral immunity.
• MCCC2 is deacetylated by SIRT4 and controls acetyl-CoA synthesis, stemness, and invasiveness in hepatocellular carcinoma.
• SLC25A21 loss induces mitochondrial GPX4 deficiency and ferroptosis in colorectal cancer, implicating MCCC-related metabolism in cell death.
• The enzyme is a biotin-dependent carboxylase, making it a model system for studying biotin chemistry and holoenzyme architecture.
• Structural studies of human MCCC provide a framework for understanding synergistic activation and substrate channeling.
• MCCC1 and MCCC2 are candidate biomarkers and therapeutic targets in metabolic and oncological research.
• The activity is relevant to newborn screening and genetic counseling for organic acidemias.
• CRISPR models of MCCC1 and MCCC2 enable causal testing of metabolic and immune phenotypes.
Molecular Mechanism of methylcrotonoyl-CoA carboxylase activity
Substrate binding and bicarbonate activation
In simple terms: The enzyme grabs its substrate and a bicarbonate molecule to prepare for carboxyl transfer.
The reaction begins with binding of 3-methylbut-2-enoyl-CoA and bicarbonate at the active site of the biotin-dependent carboxylase. The enzyme uses ATP to activate bicarbonate, forming a carboxyphosphate intermediate that subsequently carboxylates the biotin cofactor. This step is shared among biotin-dependent carboxylases and requires the biotin carboxylase domain encoded within the biotin-containing subunit.
Biotin carboxylation and carboxyl carrier function
In simple terms: A swinging arm carries the carboxyl group from one part of the enzyme to another.
The biotin cofactor is covalently attached to the biotin carboxyl carrier protein (BCCP) domain. After bicarbonate activation, the biotin is carboxylated, and the BCCP domain then translocates the carboxyl group to the carboxyltransferase active site. The BCCP domain is a defining feature of the biotin-containing subunit of methylcrotonoyl-CoA carboxylase.
Carboxyl transfer to 3-methylbut-2-enoyl-CoA
In simple terms: The carboxyl group is handed off to the substrate to make the product.
In the carboxyltransferase step, the carboxyl group is transferred from carboxybiotin to 3-methylbut-2-enoyl-CoA, yielding trans-3-methylglutaconyl-CoA. This step is catalyzed by the carboxyltransferase domain, which in human methylcrotonoyl-CoA carboxylase is formed by the MCCC2 subunit in complex with MCCC1. The overall reaction consumes ATP and produces ADP, phosphate, and protons.
Holoenzyme architecture and subunit cooperation
In simple terms: The enzyme works as a team of subunits that must fit together correctly.
Human methylcrotonoyl-CoA carboxylase is a dodecameric holoenzyme composed of MCCC1 and MCCC2 subunits. Structural analysis has revealed how the subunits assemble and how conformational changes support synergistic activation of the enzyme. Biotin-dependent carboxylases exhibit striking diversity in holoenzyme architecture and extensive conformational variability, which is important for catalysis and regulation.
Cofactor requirements and regulation
In simple terms: The enzyme needs biotin and ATP, and its activity can be tuned by cellular signals.
The activity strictly requires biotin, ATP, and bicarbonate. Biotin availability and holoenzyme assembly influence enzyme function, and mutations affecting biotin metabolism can reduce carboxylase activities. In cancer cells, MCCC2 acetylation status is regulated by SIRT4, which deacetylates MCCC2 and controls acetyl-CoA synthesis, stemness, and invasiveness. This illustrates that methylcrotonoyl-CoA carboxylase activity is not only a metabolic housekeeping function but also a regulated node in cell signaling.
Key Genes Involved in GO:0004485 methylcrotonoyl-CoA carboxylase activity
The following genes and proteins are directly or functionally linked to methylcrotonoyl-CoA carboxylase activity (GO:0004485) and its biological context.
| Gene | Major Role | Research Relevance |
|---|---|---|
| MCCC1 | Biotin-containing subunit of methylcrotonoyl-CoA carboxylase; contains biotin carboxylase and biotin-carrier domains | Catalytic core; linked to innate immune signaling via MAVS |
| MCCC2 | Beta subunit; contributes to carboxyltransferase activity and holoenzyme assembly | Regulated by SIRT4; implicated in hepatocellular carcinoma stemness and invasiveness |
| SIRT4 | Mitochondrial sirtuin that deacetylates MCCC2 | Controls acetyl-CoA synthesis and cancer cell phenotypes |
| MAVS | Mitochondrial antiviral signaling adaptor targeted by MCCC1 | Connects MCCC1 to RLR-induced NF-κB signaling |
| SLC25A21 | Mitochondrial transporter linked to MCCC-related metabolism | Loss induces ferroptosis via GPX4 deficiency in colorectal cancer |
| GPX4 | Glutathione peroxidase 4; protects against lipid peroxidation | Mitochondrial GPX4 deficiency drives ferroptosis upon SLC25A21 loss |
| NF-κB | Transcription factor downstream of RLR signaling | MCCC1 potentiates NF-κB activation through MAVS |
| ATP | Energy source for bicarbonate activation | Required co-substrate for the carboxylation reaction |
| Biotin | Covalent cofactor attached to BCCP domain | Essential for carboxyl transfer |
| Bicarbonate | Carbon source for carboxylation | Substrate for carboxyphosphate formation |
| 3-methylbut-2-enoyl-CoA | Substrate of the reaction | Intermediate in leucine catabolism |
| trans-3-methylglutaconyl-CoA | Product of the reaction | Downstream metabolite in leucine degradation |
| Acetyl-CoA carboxylase | Related biotin-dependent carboxylase | Deficiency observed in multiple carboxylase deficiency |
| MCCC holoenzyme | Dodecameric assembly of MCCC1 and MCCC2 | Structural studies reveal synergistic activation |
How Is methylcrotonoyl-CoA carboxylase activity Regulated?
Methylcrotonoyl-CoA carboxylase activity is regulated at multiple levels. The enzyme requires biotin and ATP, and its activity depends on proper holoenzyme assembly. In cancer cells, MCCC2 is deacetylated by SIRT4, which controls acetyl-CoA synthesis and promotes stemness and invasiveness in hepatocellular carcinoma. MCCC1 has been shown to potentiate RLR-induced NF-κB signaling by targeting the MAVS complex, indicating that its function can influence innate immune pathways. Additionally, loss of SLC25A21 alters mitochondrial metabolism and induces ferroptosis via GPX4 deficiency, linking MCCC-related metabolic flux to cell death regulation. These findings suggest that methylcrotonoyl-CoA carboxylase activity is integrated into broader metabolic and signaling networks.
methylcrotonoyl-CoA carboxylase activity and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| MCCC1 | 3-Methylcrotonyl-CoA carboxylase deficiency; innate immune signaling | Knockout or point-mutation cell models in hepatocytes or immune cells |
| MCCC2 | Hepatocellular carcinoma stemness and invasiveness | Knockout or overexpression in HCC cell lines; SIRT4 deacetylation mutants |
| SLC25A21 | Colorectal cancer ferroptosis via GPX4 deficiency | Knockout in colorectal cancer cells; ferroptosis assays |
| SIRT4 | Metabolic regulation of MCCC2 acetylation | Knockout or overexpression in cancer cell lines |
| MAVS | RLR-induced NF-κB signaling | Knockout or tagged knock-in in immune reporter cells |
3-Methylcrotonyl-CoA carboxylase deficiency
Deficiency of methylcrotonoyl-CoA carboxylase activity causes an inborn error of leucine catabolism known as 3-methylcrotonyl-CoA carboxylase deficiency. This condition is characterized by elevated 3-methylcrotonylglycine and 3-hydroxyisovaleric acid and is detected by newborn screening. The enzyme requires biotin, and defects in biotin metabolism can reduce carboxylase activities, as shown for acetyl-CoA carboxylase in multiple carboxylase deficiency. Molecular characterization of the biotin-containing subunit has provided the basis for understanding disease-causing mutations.
Cancer metabolism and hepatocellular carcinoma
MCCC2 is deacetylated by SIRT4, which controls acetyl-CoA synthesis and promotes stemness and invasiveness of hepatocellular carcinoma cells. This links methylcrotonoyl-CoA carboxylase activity to cancer metabolic reprogramming. In colorectal cancer, loss of SLC25A21 induces mitochondrial GPX4 deficiency and ferroptosis, further connecting MCCC-related metabolism to tumor cell death pathways.
Innate immunity and NF-κB signaling
MCCC1 potentiates RLR-induced NF-κB signaling by targeting the MAVS complex. This finding expands the role of methylcrotonoyl-CoA carboxylase activity beyond metabolism into antiviral innate immunity. Researchers studying host-pathogen interactions may therefore consider MCCC1 as a modulator of MAVS-dependent signaling.
From methylcrotonoyl-CoA carboxylase activity-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| Does MCCC1 loss alter NF-κB activation? | MCCC1 knockout cell line with RLR stimulation and NF-κB reporter |
| Does MCCC2 acetylation affect cancer stemness? | MCCC2 point-mutation (acetylation-site) knock-in in HCC cells |
| How does SIRT4 regulate MCCC2? | SIRT4 knockout or overexpression with MCCC2 acetylation assays |
| Does SLC25A21 loss induce ferroptosis? | SLC25A21 knockout colorectal cancer cells with GPX4 and lipid peroxidation readouts |
| What is the role of MCCC1 in MAVS signaling? | Tagged knock-in of MCCC1 for interaction proteomics |
| Can MCCC2 overexpression drive invasiveness? | MCCC2 overexpression in HCC cell lines with invasion assays |
How to Study the methylcrotonoyl-CoA carboxylase activity Process
| Method | What It Measures | Typical Application |
|---|---|---|
| Coupled enzymatic assay | ATP-dependent carboxylation of 3-methylbut-2-enoyl-CoA | Validation of MCCC activity in cell lysates |
| Cryo-EM / X-ray crystallography | Holoenzyme structure and conformational states | Understanding subunit assembly and catalysis |
| CRISPR knockout screening | Gene requirements for metabolic or immune phenotypes | Identifying modifiers of MCCC-related pathways |
| Targeted metabolomics | Levels of leucine catabolites | Assessing pathway flux in disease models |
| Stable isotope tracing | Carbon flux through MCCC | Distinguishing metabolic and signaling roles |
| Co-immunoprecipitation | Protein-protein interactions (e.g., MCCC1-MAVS) | Mapping immune signaling complexes |
| Acetylation assays | MCCC2 acetylation status | Studying SIRT4-mediated regulation |
| Ferroptosis assays | Lipid peroxidation and GPX4 levels | Linking MCCC-related metabolism to cell death |
Enzymatic activity assays
Methylcrotonoyl-CoA carboxylase activity can be measured using coupled enzyme assays that monitor the ATP-dependent carboxylation of 3-methylbut-2-enoyl-CoA. These assays typically use radiolabeled bicarbonate or spectrophotometric detection of ADP production. Such methods are foundational for studying the catalytic mechanism and for validating CRISPR models.
Structural biology and biophysics
Structural studies using cryo-electron microscopy and X-ray crystallography have revealed the architecture of the human MCCC holoenzyme and the conformational changes that support synergistic activation. Biophysical methods such as analytical ultracentrifugation and native mass spectrometry can assess subunit assembly and holoenzyme stoichiometry.
CRISPR screening and functional genomics
CRISPR knockout screens can identify genes that modulate methylcrotonoyl-CoA carboxylase activity or its downstream phenotypes. For example, loss of SLC25A21 induces ferroptosis via GPX4 deficiency, a phenotype that can be uncovered by genome-wide screens. Similarly, MCCC1 and MCCC2 can be tested for their roles in NF-κB signaling and cancer cell phenotypes.
Metabolomics and flux analysis
Targeted metabolomics can quantify 3-methylbut-2-enoyl-CoA, trans-3-methylglutaconyl-CoA, and related leucine catabolites to assess flux through the MCCC step. Stable isotope tracing with labeled leucine or bicarbonate can measure carbon flow and distinguish metabolic from signaling functions.
How CRISPR Can Be Used to Study GO:0004485 methylcrotonoyl-CoA carboxylase activity
Knockout
CRISPR knockout of MCCC1 or MCCC2 can abolish methylcrotonoyl-CoA carboxylase activity, enabling causal tests of its role in leucine catabolism, innate immune signaling, and cancer phenotypes. Knockout of SLC25A21 can be used to model metabolic stress and ferroptosis.
Point Mutation
Point mutations in MCCC1 or MCCC2 can be introduced to mimic disease-associated variants or to disrupt specific regulatory sites, such as acetylation sites on MCCC2 targeted by SIRT4. Such models help distinguish catalytic from non-catalytic functions.
Knock-in
Tagged knock-in of MCCC1 or MCCC2 allows endogenous labeling for interaction proteomics and imaging. For example, a tagged MCCC1 knock-in can be used to study its interaction with MAVS in immune signaling.
Overexpression
Overexpression of MCCC2 in cancer cell lines can drive stemness and invasiveness, providing a model to study its oncogenic functions. Overexpression of SIRT4 can be used to test its effects on MCCC2 acetylation and acetyl-CoA synthesis.
How EDITGENE Supports methylcrotonoyl-CoA carboxylase activity Research
Researchers studying methylcrotonoyl-CoA carboxylase activity-related genes often need to determine whether a candidate gene is causally involved in metabolic, immune, or oncogenic phenotypes. EDITGENE provides CRISPR-based cell model services to enable such causal studies.
Contact EDITGENE today to design your custom CRISPR model for methylcrotonoyl-CoA carboxylase activity research.
Frequently Asked Questions About methylcrotonoyl-CoA carboxylase activity
What is methylcrotonoyl-CoA carboxylase activity?
It is the enzymatic activity (GO:0004485) that catalyzes the ATP- and biotin-dependent carboxylation of 3-methylbut-2-enoyl-CoA to trans-3-methylglutaconyl-CoA, a step in leucine catabolism.
What genes are involved in methylcrotonoyl-CoA carboxylase activity?
The core genes are MCCC1 and MCCC2, which encode the subunits of the human holoenzyme. SIRT4, MAVS, and SLC25A21 are functionally linked.
What is the reaction catalyzed by GO:0004485?
3-methylbut-2-enoyl-CoA + ATP + bicarbonate = trans-3-methylglutaconyl-CoA + ADP + 2 H+ + phosphate.
What diseases are associated with methylcrotonoyl-CoA carboxylase deficiency?
Deficiency causes 3-methylcrotonyl-CoA carboxylase deficiency, an inborn error of leucine metabolism. MCCC2 is also implicated in hepatocellular carcinoma, and SLC25A21 loss is linked to ferroptosis in colorectal cancer.
How is methylcrotonoyl-CoA carboxylase activity regulated?
It requires biotin and ATP, depends on holoenzyme assembly, and is regulated by SIRT4-mediated deacetylation of MCCC2 in cancer cells.
What is the role of MCCC1 in immune signaling?
MCCC1 potentiates RLR-induced NF-κB signaling by targeting the MAVS complex.
How can I study methylcrotonoyl-CoA carboxylase activity in the lab?
Use coupled enzymatic assays, metabolomics, structural biology, and CRISPR knockout or overexpression models.
What cell models are available for MCCC2 research?
Knockout, point-mutation, and overexpression models in cancer cell lines can be used to study MCCC2 acetylation, stemness, and invasiveness.
Is methylcrotonoyl-CoA carboxylase activity involved in ferroptosis?
Loss of SLC25A21, which is linked to MCCC-related metabolism, induces ferroptosis via mitochondrial GPX4 deficiency in colorectal cancer.
What is the structure of human methylcrotonoyl-CoA carboxylase?
It is a dodecameric holoenzyme composed of MCCC1 and MCCC2 subunits, with structural studies revealing synergistic activation.
Conclusion
Methylcrotonoyl-CoA carboxylase activity (GO:0004485) is a biotin-dependent carboxylation that serves as a committed step in leucine catabolism and is carried out by the MCCC1-MCCC2 holoenzyme. Beyond metabolism, its subunits have been linked to innate immune signaling through MAVS and to cancer phenotypes such as stemness, invasiveness, and ferroptosis. Understanding this activity therefore requires integrating enzymology, structural biology, and functional genomics. CRISPR-based cell models provide a powerful approach to test causal roles of MCCC1, MCCC2, and related genes in health and disease.
References
- 1. Cao Z et al.. 2016. Methylcrotonoyl-CoA carboxylase 1 potentiates RLR-induced NF-κB signaling by targeting MAVS complex.. Sci Rep 6:33557 PMID: 27629939
- 2. Feldman GL et al.. 1981. Deficient acetyl CoA carboxylase activity in multiple carboxylase deficiency.. Clin Chim Acta 111(2-3):147-51 PMID: 6112081
- 3. Song J et al.. 1994. Molecular cloning and characterization of the cDNA coding for the biotin-containing subunit of 3-methylcrotonoyl-CoA carboxylase: identification of the biotin carboxylase and biotin-carrier domains.. Proc Natl Acad Sci U S A 91(13):5779-83 PMID: 8016064
- 4. Sun T et al.. 2025. SIRT4 Controls Acetyl-CoA Synthesis to Promote Stemness and Invasiveness of Hepatocellular Carcinoma through Deacetylating MCCC2.. Int J Biol Sci 21(7):2973-2990 PMID: 40384857
- 5. Tong L. 2013. Structure and function of biotin-dependent carboxylases.. Cell Mol Life Sci 70(5):863-91 PMID: 22869039
- 6. Tong L. 2017. Striking Diversity in Holoenzyme Architecture and Extensive Conformational Variability in Biotin-Dependent Carboxylases.. Adv Protein Chem Struct Biol 109:161-194 PMID: 28683917
- 7. Liu W et al.. 2026. SLC25A21 promotes ferroptosis by inducing mitochondrial GPX4 deficiency in colorectal cancer.. Cell Mol Life Sci 83(1) PMID: 42012504
- 8. Su J et al.. 2025. Structural insight into synergistic activation of human 3-methylcrotonyl-CoA carboxylase.. Nat Struct Mol Biol 32(1):73-85 PMID: 39223421
