GO:0004490 methylglutaconyl-CoA hydratase activity: Mechanism, Genes and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0004490 methylglutaconyl-CoA hydratase activity catalyzes the reversible hydration of trans-3-methylglutaconyl-CoA to (S)-3-hydroxy-3-methylglutaryl-CoA, the penultimate step of leucine catabolism.
• The enzyme belongs to the crotonase superfamily and uses a conserved glutamate as catalytic base, with a mechanism that has been dissected in both human and Pseudomonas putida orthologs.
• In humans, the activity is encoded by AUH (3-methylglutaconyl-CoA hydratase), and biallelic AUH mutations cause 3-methylglutaconic aciduria type I.
• Not all patients with 3-methylglutaconic aciduria have a defect in this activity, so enzyme assays and AUH sequencing are required for a molecular diagnosis.
• AUH is a bifunctional protein: it also acts as an RNA-binding protein that regulates brown adipose tissue thermogenesis via PPARγ HMGylation.
• CRISPR knockout, point-mutation, knock-in and overexpression models are essential to separate the hydratase activity from the RNA-binding function of AUH.
Description
GO:0004490 methylglutaconyl-CoA hydratase activity is a molecular function defined as the catalysis of the reaction (S)-3-hydroxy-3-methylglutaryl-CoA = trans-3-methylglutaconyl-CoA + H2O. This reversible dehydration/hydration step is the fourth enzymatic reaction in the leucine catabolic pathway, converting the CoA thioester of 3-methylglutaconyl-CoA into 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA). The activity is therefore a central node connecting branched-chain amino acid degradation to ketogenesis and sterol biosynthesis. In humans, the enzyme is encoded by the AUH gene, and its deficiency is one of the few inborn errors of leucine metabolism that can be diagnosed by urinary organic acid analysis. Beyond its canonical metabolic role, recent work has shown that AUH is a bifunctional protein with RNA-binding activity that regulates thermogenesis, making GO:0004490 a function of interest in both metabolic disease and gene regulation. For researchers, the term provides a precise functional annotation for interpreting variants, designing enzyme assays, and building CRISPR models that separate catalytic from non-catalytic roles.
methylglutaconyl-CoA hydratase activity At A Glance
| GO ID | GO:0004490 |
|---|---|
| GO term | methylglutaconyl-CoA hydratase activity |
| Ontology | molecular_function |
| Definition | Catalysis of the reaction: (S)-3-hydroxy-3-methylglutaryl-CoA = trans-3-methylglutaconyl-CoA + H2O. |
| Synonyms | 3-methylglutaconyl CoA hydratase activity; methylglutaconase activity; methylglutaconyl coenzyme A hydratase activity; (S)-3-hydroxy-3-methylglutaryl-CoA hydro-lyase activity; (S)-3-hydroxy-3-methylglutaryl-CoA hydro-lyase (trans-3-methylglutaconyl-CoA-forming) |
| Major function | Reversible hydration/dehydration step in leucine catabolism, interconverting 3-methylglutaconyl-CoA and 3-hydroxy-3-methylglutaryl-CoA. |
| Human gene | AUH (3-methylglutaconyl-CoA hydratase) |
| Pathway | Leucine degradation (branched-chain amino acid catabolism) |
| Associated disease | 3-methylglutaconic aciduria type I (AUH deficiency) |
What Is GO:0004490?
In simple terms, GO:0004490 describes an enzyme that adds or removes a water molecule from a CoA-linked intermediate during leucine breakdown. Formally, the term refers to catalysis of the reversible reaction (S)-3-hydroxy-3-methylglutaryl-CoA = trans-3-methylglutaconyl-CoA + H2O. The enzyme is also known as 3-methylglutaconyl-CoA hydratase, methylglutaconase, or (S)-3-hydroxy-3-methylglutaryl-CoA hydro-lyase. It belongs to the enoyl-CoA hydratase/isomerase (crotonase) superfamily and uses a glutamate residue as a general acid/base to activate water for addition across the double bond of trans-3-methylglutaconyl-CoA.
Why Is methylglutaconyl-CoA hydratase activity Important in Cell Biology?
GO:0004490 is important because it defines the catalytic step that links leucine catabolism to HMG-CoA, a metabolite at the crossroads of ketogenesis and cholesterol synthesis. Loss of this activity causes 3-methylglutaconic aciduria type I, an inborn error of metabolism with neurological involvement. The same activity is also a model system for understanding the crotonase superfamily, where a conserved glutamate and oxyanion hole catalyze hydration of diverse CoA thioesters. Finally, the AUH protein that carries this activity has a second, RNA-binding function, so the hydratase annotation is essential for interpreting genotype-phenotype relationships and for designing experiments that separate catalytic from non-catalytic roles.
• Provides a precise functional annotation for the AUH gene product in leucine catabolism.
• Enables molecular diagnosis of 3-methylglutaconic aciduria type I when AUH mutations are found.
• Helps distinguish true hydratase deficiency from other causes of 3-methylglutaconic aciduria.
• Serves as a paradigm for crotonase superfamily catalysis and substrate specificity.
• Connects branched-chain amino acid degradation to HMG-CoA and ketone body production.
• Supports newborn screening and selective screening programs for organic acidurias.
• Provides a target for studying bifunctional metabolic enzymes with RNA-binding roles.
• Guides CRISPR model design to test whether catalytic activity is required for thermogenesis.
• Offers a biomarker context for 3-methylglutaconic acid in urine and plasma.
• Informs structure-function studies of the enoyl-CoA hydratase/isomerase fold.
Molecular Mechanism of methylglutaconyl-CoA hydratase activity
Substrate binding and the crotonase fold
In simple terms: The enzyme grabs a CoA-linked substrate inside a barrel-shaped pocket.
The enzyme belongs to the crotonase superfamily, characterized by a dimeric or trimeric assembly of α/β barrel subunits that form a deep substrate-binding tunnel. The CoA moiety is anchored by hydrogen bonds and hydrophobic contacts, positioning the trans-3-methylglutaconyl-CoA double bond for hydration. In the human enzyme, the active site accommodates the branched methyl group of the substrate, which distinguishes it from canonical enoyl-CoA hydratases.
Catalytic base and oxyanion hole
In simple terms: A glutamate residue pulls a proton and water attacks the double bond.
A conserved glutamate (Glu) acts as a general acid/base. In the hydration direction, it deprotonates a water molecule, which then attacks the β-carbon of trans-3-methylglutaconyl-CoA. The resulting enolate/oxyanion is stabilized by backbone amides in an oxyanion hole. The reaction is reversible, and the equilibrium favors the hydration direction under physiological conditions.
Reaction direction and metabolic context
In simple terms: The enzyme can run both ways, but in cells it usually helps break down leucine.
The reaction interconverts (S)-3-hydroxy-3-methylglutaryl-CoA and trans-3-methylglutaconyl-CoA. In leucine catabolism, the flux is toward HMG-CoA, which is then cleaved to acetoacetate and acetyl-CoA. The reversibility allows the enzyme to buffer HMG-CoA pools, linking leucine degradation to ketogenesis and sterol synthesis.
Bifunctional roles beyond catalysis
In simple terms: The same protein can also bind RNA and control gene expression.
Human AUH is a bifunctional protein. In addition to its hydratase activity, it binds RNA and regulates the stability or translation of specific transcripts. A recent study showed that AUH regulates brown adipose tissue thermogenesis via PPARγ HMGylation and its RNA-binding function, indicating that the protein has catalytic and non-catalytic roles that can be separated experimentally.
Key Genes Involved in GO:0004490 methylglutaconyl-CoA hydratase activity
The following genes and proteins are directly or indirectly associated with GO:0004490 methylglutaconyl-CoA hydratase activity.
| Gene | Major Role | Research Relevance |
|---|---|---|
| AUH | Encodes the human 3-methylglutaconyl-CoA hydratase; catalyzes the hydration/dehydration step in leucine catabolism | Mutations cause 3-methylglutaconic aciduria type I; target for enzyme assays and CRISPR models |
| HMGCL | Encodes 3-hydroxy-3-methylglutaryl-CoA lyase, the next enzyme in leucine catabolism | Defects cause HMG-CoA lyase deficiency, a differential diagnosis for 3-methylglutaconic aciduria |
| HMGCS1 | Cytosolic HMG-CoA synthase, produces HMG-CoA for sterol synthesis | Context for HMG-CoA pool regulation |
| HMGCS2 | Mitochondrial HMG-CoA synthase, involved in ketogenesis | Links leucine catabolism to ketone body production |
| ACAT1 | Acetoacetyl-CoA thiolase, upstream of HMG-CoA in ketogenesis | Metabolic context for HMG-CoA flux |
| BCKDHA | Branched-chain α-ketoacid dehydrogenase E1α, upstream of leucine catabolism | Defects cause maple syrup urine disease, altering leucine flux |
| BCKDHB | Branched-chain α-ketoacid dehydrogenase E1β | Upstream regulator of leucine catabolism |
| DBT | Dihydrolipoamide branched-chain transacylase, BCKD complex | Upstream of AUH in the pathway |
| DLD | Dihydrolipoamide dehydrogenase, BCKD complex | Upstream of AUH in the pathway |
| IVD | Isovaleryl-CoA dehydrogenase, third step of leucine catabolism | Defects cause isovaleric acidemia, a differential diagnosis |
| MCCC1 | Methylcrotonoyl-CoA carboxylase α subunit, upstream of AUH | Defects cause 3-methylcrotonyl-CoA carboxylase deficiency |
| MCCC2 | Methylcrotonoyl-CoA carboxylase β subunit | Upstream of AUH in leucine catabolism |
| PPARG | Peroxisome proliferator-activated receptor gamma, target of HMGylation by AUH | Links AUH to thermogenesis and gene regulation |
| UCP1 | Uncoupling protein 1, marker of brown adipocytes | Readout of AUH-dependent thermogenesis |
| P. putida mgh | Bacterial (3S)-methylglutaconyl-CoA hydratase, model for crotonase superfamily | Provides structural and mechanistic insights into GO:0004490 |
How Is methylglutaconyl-CoA hydratase activity Regulated?
The expression and activity of methylglutaconyl-CoA hydratase are regulated at multiple levels. Transcription of AUH is responsive to metabolic state, and the protein is subject to post-translational modification. In brown adipose tissue, AUH regulates PPARγ activity through HMGylation, and its RNA-binding function modulates thermogenic gene expression. The enzyme's catalytic activity can also be influenced by substrate availability, as flux through leucine catabolism depends on upstream BCKD complex activity. No direct allosteric regulators of the hydratase have been reported in the cited literature.
methylglutaconyl-CoA hydratase activity and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| AUH | 3-Methylglutaconic aciduria type I | AUH knockout HEK293 or patient fibroblasts; enzyme activity assay |
| AUH | Thermogenesis regulation via PPARγ HMGylation | AUH knockout brown adipocytes; UCP1 expression |
| HMGCL | HMG-CoA lyase deficiency | HMGCL knockout hepatocytes; acylcarnitine profiling |
| MCCC1/MCCC2 | 3-Methylcrotonyl-CoA carboxylase deficiency | Knockout cell lines; organic acid analysis |
| IVD | Isovaleric acidemia | IVD knockout fibroblasts; leucine flux assay |
3-Methylglutaconic aciduria type I
Biallelic mutations in AUH cause 3-methylglutaconic aciduria type I, an inborn error of leucine metabolism characterized by elevated urinary 3-methylglutaconic acid and 3-methylglutaric acid. Patients may present with developmental delay, speech delay, and neurological symptoms. The diagnosis is confirmed by enzyme assay or molecular testing of AUH.
Differential diagnosis of 3-methylglutaconic aciduria
Not all patients with 3-methylglutaconic aciduria have a defect in methylglutaconyl-CoA hydratase activity. Some patients excrete the metabolite due to other metabolic or mitochondrial disorders, and enzyme activity can be normal. Therefore, measurement of hydratase activity and AUH sequencing are necessary to distinguish type I from other forms.
Metabolic and thermogenic roles
AUH is a bifunctional protein that also regulates brown adipose tissue thermogenesis via PPARγ HMGylation and RNA binding. This links GO:0004490 to energy homeostasis and suggests that AUH dysfunction may have consequences beyond leucine catabolism.
From methylglutaconyl-CoA hydratase activity-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| Does loss of AUH hydratase activity cause 3-methylglutaconic aciduria? | AUH knockout HEK293 or HAP1 cells; LC-MS of organic acids |
| Is the catalytic glutamate required for leucine catabolism? | Point mutation of the catalytic Glu in AUH; enzyme assay |
| Does AUH RNA-binding require hydratase activity? | Knock-in of catalytically dead AUH; RNA immunoprecipitation |
| How does AUH regulate PPARγ HMGylation? | Tagged knock-in of AUH; co-immunoprecipitation and mass spectrometry |
| Can AUH overexpression rescue thermogenesis? | Overexpression of AUH in brown adipocytes; UCP1 reporter |
| What is the substrate specificity of AUH? | Recombinant AUH purified from E. coli; kinetic assays with CoA thioesters |
How to Study the methylglutaconyl-CoA hydratase activity Process
| Method | What It Measures | Typical Application |
|---|---|---|
| UV spectrophotometric assay | Hydratase activity via absorbance change at 300 nm | Kinetic characterization of recombinant AUH |
| GC-MS organic acid analysis | Urinary 3-methylglutaconic and 3-methylglutaric acid | Diagnosis of 3-methylglutaconic aciduria |
| Sanger sequencing | AUH mutations | Molecular confirmation of type I aciduria |
| CRISPR knockout | Loss of AUH function | Modeling AUH deficiency in cells |
| CRISPR point mutation | Catalytic residue requirement | Separating hydratase from RNA-binding function |
| RNA immunoprecipitation | AUH-RNA interactions | Studying non-catalytic roles |
| Western blot | AUH protein levels | Validating knockout or overexpression |
| LC-MS/MS | Acylcarnitines and CoA thioesters | Metabolic flux analysis |
Enzyme activity assays
Methylglutaconyl-CoA hydratase activity can be measured spectrophotometrically by following the decrease in absorbance at 300 nm as trans-3-methylglutaconyl-CoA is hydrated to HMG-CoA. Recombinant human AUH expressed in E. coli is used for kinetic characterization. Bacterial orthologs can be assayed similarly.
Organic acid analysis
Urinary organic acid analysis by gas chromatography-mass spectrometry (GC-MS) detects elevated 3-methylglutaconic and 3-methylglutaric acids, the hallmark of AUH deficiency. This method is used for screening and diagnosis.
Molecular genetics
Sanger sequencing or next-generation sequencing of AUH is used to identify pathogenic variants in patients with 3-methylglutaconic aciduria. This confirms the diagnosis and enables carrier testing.
CRISPR-based functional studies
CRISPR knockout, point mutation, and knock-in models allow researchers to test the requirement of AUH catalytic activity for leucine catabolism and thermogenesis. Overexpression models can assess gain-of-function effects.
How CRISPR Can Be Used to Study GO:0004490 methylglutaconyl-CoA hydratase activity
Knockout
CRISPR knockout of AUH in HEK293 or HAP1 cells abolishes methylglutaconyl-CoA hydratase activity and causes accumulation of 3-methylglutaconyl-CoA, modeling 3-methylglutaconic aciduria type I. These models are used to confirm variant pathogenicity and to study metabolic consequences.
Point Mutation
Point mutation of the catalytic glutamate in AUH (e.g., Glu to Gln) generates a catalytically dead enzyme that can be used to test whether hydratase activity is required for leucine catabolism or for the RNA-binding function. This is critical for separating the dual roles of AUH.
Knock-in
Knock-in of epitope-tagged AUH (e.g., FLAG or HA) allows endogenous-level expression and purification for interaction studies. Knock-in of patient-specific mutations recreates the disease genotype in isogenic cell lines.
Overexpression
Overexpression of wild-type or mutant AUH in brown adipocytes or other cell types can test gain-of-function effects on PPARγ HMGylation, UCP1 expression, and thermogenesis. This complements loss-of-function studies.
How EDITGENE Supports methylglutaconyl-CoA hydratase activity Research
Researchers studying methylglutaconyl-CoA hydratase activity-related genes often need to determine whether a candidate gene is causally involved in leucine catabolism, metabolic disease, or thermogenesis. EDITGENE provides a full suite of CRISPR services to build precisely engineered cell models that answer these questions.
Contact EDITGENE today to design your custom CRISPR model for methylglutaconyl-CoA hydratase activity research.
Frequently Asked Questions About methylglutaconyl-CoA hydratase activity
What is methylglutaconyl-CoA hydratase activity?
It is the enzymatic activity defined by GO:0004490 that catalyzes the reversible hydration of trans-3-methylglutaconyl-CoA to (S)-3-hydroxy-3-methylglutaryl-CoA, a step in leucine catabolism.
What gene encodes methylglutaconyl-CoA hydratase in humans?
The AUH gene encodes the human 3-methylglutaconyl-CoA hydratase.
What disease is caused by methylglutaconyl-CoA hydratase deficiency?
Biallelic AUH mutations cause 3-methylglutaconic aciduria type I, characterized by elevated urinary 3-methylglutaconic acid.
Do all patients with 3-methylglutaconic aciduria have a hydratase defect?
No, some patients have normal enzyme activity, so additional testing is needed to identify the cause.
What is the reaction catalyzed by GO:0004490?
The reaction is (S)-3-hydroxy-3-methylglutaryl-CoA = trans-3-methylglutaconyl-CoA + H2O.
What pathway is methylglutaconyl-CoA hydratase involved in?
It is part of the leucine degradation pathway, also known as branched-chain amino acid catabolism.
How is methylglutaconyl-CoA hydratase activity measured?
It can be measured spectrophotometrically by following the absorbance change at 300 nm using recombinant enzyme.
What is the role of AUH in thermogenesis?
AUH regulates brown adipose tissue thermogenesis via PPARγ HMGylation and its RNA-binding function.
What model systems are used to study AUH deficiency?
CRISPR knockout cell lines, patient fibroblasts, and mouse models are used to study AUH deficiency.
What are the synonyms for methylglutaconyl-CoA hydratase activity?
Synonyms include 3-methylglutaconyl CoA hydratase activity, methylglutaconase activity, and (S)-3-hydroxy-3-methylglutaryl-CoA hydro-lyase activity.
Conclusion
GO:0004490 methylglutaconyl-CoA hydratase activity defines a critical enzymatic step in leucine catabolism with direct links to 3-methylglutaconic aciduria type I and emerging roles in thermogenesis. The AUH gene encodes this activity, and its bifunctional nature makes it a compelling target for CRISPR-based dissection. Understanding the mechanism, regulation, and disease associations of this activity provides a foundation for diagnostic and therapeutic research.
References
- 1. Mack M et al.. 2006. Biochemical characterization of human 3-methylglutaconyl-CoA hydratase and its role in leucine metabolism.. FEBS J 273(9):2012-22 PMID: 16640564
- 2. Wong BJ et al.. 2004. Evolution of function in the crotonase superfamily: (3S)-methylglutaconyl-CoA hydratase from Pseudomonas putida.. Biochemistry 43(16):4646-54 PMID: 15096032
- 3. Gibson KM et al.. 1988. 3-Methylglutaconic aciduria: a phenotype in which activity of 3-methylglutaconyl-coenzyme A hydratase is normal.. Eur J Pediatr 148(1):76-82 PMID: 3197737
- 4. Narisawa K et al.. 1986. Deficiency of 3-methylglutaconyl-coenzyme A hydratase in two siblings with 3-methylglutaconic aciduria.. J Clin Invest 77(4):1148-52 PMID: 3082934
- 5. Lehnert W et al.. 1985. 3-Methylglutaconic and 3-methylglutaric aciduria in a patient with suspected 3-methylglutaconyl-CoA hydratase deficiency.. Eur J Pediatr 143(4):301-3 PMID: 2580710
- 6. Gibson KM et al.. 1994. Screening for defects of branched-chain amino acid metabolism.. Eur J Pediatr 153(7 Suppl 1):S62-7 PMID: 7957389
- 7. Ly TB et al.. 2003. Mutations in the AUH gene cause 3-methylglutaconic aciduria type I.. Hum Mutat 21(4):401-7 PMID: 12655555
- 8. Jiang H et al.. 2026. Leucine catabolic enzyme AUH regulates BAT thermogenesis via PPARγ HMGylation and RNA-binding function in male mice.. Nat Commun 17(1) PMID: 41963339
