GO:0120567 hydroxytrimethyllysine aldolase activity: Mechanism, Genes and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0120567 (hydroxytrimethyllysine aldolase activity, synonym HTMLA) is a molecular_function defined as the catalysis of the reaction: (3S)-3-hydroxy-N(6),N(6),N(6)-trimethyl-L-lysine = 4-(trimethylamino)butanal + glycine.
• HTMLA is a key enzyme in the carnitine biosynthesis pathway, converting (3S)-3-hydroxy-N(6),N(6),N(6)-trimethyl-L-lysine to 4-(trimethylamino)butanal and glycine.
• In humans and mice, the gene encoding HTMLA was recently identified through virtual screening and experimental validation, filling a long-standing gap in the carnitine biosynthesis pathway.
• The complete carnitine biosynthesis pathway, including HTMLA activity, has been characterized in Candida albicans, providing a fungal model for studying this enzyme.
• Defects in carnitine biosynthesis can lead to carnitine deficiency disorders, affecting fatty acid oxidation and energy metabolism.
• Researchers study HTMLA using CRISPR knockout, point mutation, knock-in, and overexpression models, combined with metabolomics and enzyme assays [1,2].
Description
Hydroxytrimethyllysine aldolase activity (GO:0120567) is a molecular function that catalyzes the cleavage of (3S)-3-hydroxy-N(6),N(6),N(6)-trimethyl-L-lysine into 4-(trimethylamino)butanal and glycine. This reaction is a critical step in the carnitine biosynthesis pathway, which is essential for fatty acid transport into mitochondria and energy production. Despite its importance, the enzyme responsible for this activity in humans and mice was only recently identified through a combination of computational and experimental approaches. In the yeast Candida albicans, a complete carnitine biosynthesis pathway including this activity has been characterized, offering insights into the evolutionary conservation of the pathway. Understanding hydroxytrimethyllysine aldolase activity is therefore crucial for researchers studying carnitine metabolism, mitochondrial function, and related metabolic disorders.
hydroxytrimethyllysine aldolase activity At A Glance
| GO ID | GO:0120567 |
|---|---|
| GO term | hydroxytrimethyllysine aldolase activity |
| Ontology | molecular_function |
| Synonym | HTMLA |
| Definition | Catalysis of the reaction: (3S)-3-hydroxy-N(6),N(6),N(6)-trimethyl-L-lysine = 4-(trimethylamino)butanal + glycine. |
| Major function | Catalyzes a step in carnitine biosynthesis |
| Pathway | Carnitine biosynthesis |
| Substrate | (3S)-3-hydroxy-N(6),N(6),N(6)-trimethyl-L-lysine |
| Products | 4-(trimethylamino)butanal and glycine |
What Is GO:0120567?
Hydroxytrimethyllysine aldolase activity (GO:0120567) is defined as the catalysis of the reaction: (3S)-3-hydroxy-N(6),N(6),N(6)-trimethyl-L-lysine = 4-(trimethylamino)butanal + glycine. In other words, it is an aldolase that breaks down a trimethyllysine derivative into two products, one of which is a precursor for carnitine synthesis.
Why Is hydroxytrimethyllysine aldolase activity Important in Cell Biology?
Hydroxytrimethyllysine aldolase activity is essential for carnitine biosynthesis, a process required for the transport of long-chain fatty acids into mitochondria for beta-oxidation and energy production. Carnitine deficiency can lead to severe metabolic disorders, including cardiomyopathy, skeletal myopathy, and hypoglycemia. The recent identification of the gene encoding this activity in humans and mice has opened new avenues for studying carnitine-related diseases and for developing therapeutic strategies. Furthermore, the presence of this activity in Candida albicans highlights its importance in microbial metabolism and potential as an antifungal target.
• Critical for carnitine biosynthesis and fatty acid oxidation.
• Defects can cause carnitine deficiency disorders.
• Provides a target for studying mitochondrial energy metabolism.
• Conserved in fungi such as Candida albicans.
• Enables metabolic engineering for carnitine production.
• Potential role in diseases linked to impaired fatty acid oxidation.
• Useful for understanding enzyme evolution and substrate specificity.
• Can be studied using CRISPR-based gene editing [1,2].
Molecular Mechanism of hydroxytrimethyllysine aldolase activity
Substrate Recognition and Binding
In simple terms: The enzyme grabs its target molecule, a modified lysine, and holds it in place.
Hydroxytrimethyllysine aldolase specifically binds (3S)-3-hydroxy-N(6),N(6),N(6)-trimethyl-L-lysine, a trimethylated lysine derivative. This substrate is generated in the carnitine biosynthesis pathway. The enzyme's active site is tailored to accommodate this substrate, ensuring high specificity.
Catalytic Cleavage
In simple terms: The enzyme cuts the molecule into two pieces: a smaller one called glycine and a larger one that continues down the carnitine pathway.
The aldolase catalyzes the cleavage of the substrate into 4-(trimethylamino)butanal and glycine. This retro-aldol reaction likely involves the formation of a Schiff base intermediate with a catalytic lysine residue, although the exact mechanism remains to be fully elucidated.
Product Release and Pathway Continuation
In simple terms: The products are released, and the larger piece goes on to become carnitine.
After cleavage, 4-(trimethylamino)butanal is further processed by downstream enzymes to eventually form carnitine. Glycine is released as a byproduct. The efficient release of products is crucial for maintaining flux through the pathway.
Cofactors and Regulation
In simple terms: The enzyme might need helper molecules and can be turned on or off.
The cofactor requirements for hydroxytrimethyllysine aldolase are not fully defined, but similar aldolases often require pyridoxal phosphate. Regulation may occur at the transcriptional level or via substrate availability, as seen in other carnitine biosynthesis enzymes [1,2].
Key Genes Involved in GO:0120567 hydroxytrimethyllysine aldolase activity
The following genes and proteins are involved in hydroxytrimethyllysine aldolase activity and related carnitine biosynthesis pathways.
| Gene | Major Role | Research Relevance |
|---|---|---|
| HTMLA (human) | Encodes hydroxytrimethyllysine aldolase | Recently identified; mutations may affect carnitine synthesis |
| HTMLA (mouse) | Ortholog of human HTMLA | Model for studying carnitine biosynthesis in vivo |
| Candida albicans homolog | Catalyzes same reaction in fungi | Fungal model for pathway analysis |
| TMLH | Trimethyllysine hydroxylase | Upstream enzyme in carnitine biosynthesis |
| HTMLA | Hydroxytrimethyllysine aldolase | Directly catalyzes the reaction |
| BBOX1 | Gamma-butyrobetaine hydroxylase | Downstream enzyme in carnitine biosynthesis |
| SLC25A20 | Carnitine-acylcarnitine translocase | Transports carnitine derivatives into mitochondria |
| CPT1A | Carnitine palmitoyltransferase 1 | Rate-limiting for fatty acid oxidation |
| CPT2 | Carnitine palmitoyltransferase 2 | Mitochondrial beta-oxidation |
| ACADVL | Very long-chain acyl-CoA dehydrogenase | Fatty acid oxidation |
| HADHA | Trifunctional protein subunit alpha | Mitochondrial fatty acid oxidation |
| ETFA | Electron transfer flavoprotein alpha | Fatty acid oxidation |
| SLC22A5 | Carnitine transporter | Cellular carnitine uptake |
| PPARα | Regulator of lipid metabolism | Transcriptional control of carnitine pathway |
| PGC-1α | Mitochondrial biogenesis regulator | May influence carnitine biosynthesis |
| AMPK | Energy sensor | Regulates fatty acid oxidation |
| mTOR | Growth regulator | May affect carnitine pathway |
How Is hydroxytrimethyllysine aldolase activity Regulated?
The regulation of hydroxytrimethyllysine aldolase activity is not well characterized, but it is likely controlled at the transcriptional level in response to metabolic demands. In Candida albicans, the carnitine biosynthesis pathway is regulated by the availability of precursors and may be subject to feedback inhibition. In mammals, PPARα and PGC-1α are known to regulate genes involved in fatty acid oxidation and mitochondrial function, which could indirectly influence carnitine biosynthesis.
hydroxytrimethyllysine aldolase activity and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| HTMLA | Carnitine deficiency | Knockout mouse, patient-derived cells |
| CPT2 | CPT2 deficiency | Knockout cell lines, patient fibroblasts |
| SLC22A5 | Primary carnitine deficiency | Knockout mice, iPSC-derived cardiomyocytes |
| Candida albicans homolog | Fungal virulence | C. albicans knockout strains |
| BBOX1 | Carnitine biosynthesis defect | Knockout models |
Carnitine Deficiency Disorders
Deficiencies in carnitine biosynthesis, including impaired hydroxytrimethyllysine aldolase activity, can lead to primary carnitine deficiency, characterized by cardiomyopathy, skeletal myopathy, and hypoglycemia. The recent identification of the human HTMLA gene allows for genetic testing and potential therapeutic interventions.
Mitochondrial Fatty Acid Oxidation Defects
Reduced carnitine levels due to defective hydroxytrimethyllysine aldolase activity can impair mitochondrial fatty acid oxidation, leading to accumulation of toxic fatty acid intermediates and energy deficiency. This is particularly relevant in disorders such as CPT2 deficiency and VLCAD deficiency.
Fungal Pathogenesis
In Candida albicans, the carnitine biosynthesis pathway, including hydroxytrimethyllysine aldolase activity, is important for growth on non-fermentable carbon sources and may contribute to virulence. Targeting this enzyme could be a strategy for antifungal development.
From hydroxytrimethyllysine aldolase activity-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| Does HTMLA knockout reduce carnitine levels? | CRISPR knockout in HepG2 or HEK293 cells |
| Does a point mutation in HTMLA affect enzyme activity? | Point mutation knock-in in cell lines |
| Can HTMLA overexpression increase carnitine production? | Overexpression in mammalian cells |
| Is HTMLA essential for Candida albicans growth? | CRISPR knockout in C. albicans |
| What is the subcellular localization of HTMLA? | Tagged knock-in with GFP |
| Does HTMLA interact with other carnitine biosynthesis enzymes? | Co-immunoprecipitation in knockout background |
How to Study the hydroxytrimethyllysine aldolase activity Process
| Method | What It Measures | Typical Application |
|---|---|---|
| Enzyme assay | Catalytic activity of HTMLA | Kinetic studies, inhibitor testing |
| LC-MS metabolomics | Carnitine and intermediates | Pathway flux analysis |
| CRISPR knockout | Gene function | Loss-of-function studies |
| RNA-seq | Gene expression | Transcriptional regulation |
| Western blot | Protein levels | Validation of knockout/overexpression |
| Immunofluorescence | Subcellular localization | Organelle targeting |
| Co-IP | Protein interactions | Complex formation |
| Yeast complementation | Functional conservation | Heterologous expression |
Enzymatic Activity Assays
Direct measurement of hydroxytrimethyllysine aldolase activity using purified enzyme or cell lysates, monitoring the formation of 4-(trimethylamino)butanal or glycine by HPLC or mass spectrometry.
Metabolomics
Quantification of carnitine and its precursors in cells or tissues to assess pathway flux. This can reveal the impact of genetic perturbations on hydroxytrimethyllysine aldolase activity.
CRISPR Screening
Genome-wide knockout screens to identify genes that modulate carnitine levels or sensitivity to fatty acid oxidation inhibitors, potentially uncovering regulators of HTMLA.
Transcriptomics and Proteomics
RNA-seq and mass spectrometry to study expression changes in carnitine biosynthesis genes under different metabolic conditions [1,2].
How CRISPR Can Be Used to Study GO:0120567 hydroxytrimethyllysine aldolase activity
Knockout
CRISPR knockout of the HTMLA gene in human cell lines (e.g., HepG2) can abolish hydroxytrimethyllysine aldolase activity, leading to reduced carnitine levels and impaired fatty acid oxidation. This model is useful for studying the metabolic consequences of enzyme loss.
Point Mutation
Introducing specific point mutations in the HTMLA active site can help identify catalytic residues and understand the enzyme's mechanism. Such models can also mimic patient mutations if identified.
Knock-in
Knock-in of a tagged version of HTMLA (e.g., GFP or FLAG) allows for localization and interaction studies without affecting endogenous regulation. This is valuable for understanding the enzyme's role in the carnitine biosynthesis complex.
Overexpression
Overexpression of HTMLA in cells can increase carnitine production and may be used to study the effects of enhanced pathway flux on mitochondrial function and energy metabolism.
How EDITGENE Supports hydroxytrimethyllysine aldolase activity Research
Researchers studying hydroxytrimethyllysine aldolase activity-related genes often need to determine whether a candidate gene is causally involved in carnitine biosynthesis or related metabolic pathways. EDITGENE provides comprehensive CRISPR-based services to create precise cell models for such investigations.
Contact EDITGENE today to design your custom CRISPR model for hydroxytrimethyllysine aldolase activity research.
Frequently Asked Questions About hydroxytrimethyllysine aldolase activity
What is hydroxytrimethyllysine aldolase activity?
It is a molecular function (GO:0120567) that catalyzes the conversion of (3S)-3-hydroxy-N(6),N(6),N(6)-trimethyl-L-lysine to 4-(trimethylamino)butanal and glycine, a step in carnitine biosynthesis.
What genes are involved in hydroxytrimethyllysine aldolase activity?
The gene encoding this activity was recently identified in humans and mice, and a homolog exists in Candida albicans [1,2].
What is the role of hydroxytrimethyllysine aldolase in carnitine biosynthesis?
It catalyzes the cleavage of a trimethyllysine derivative to produce a precursor for carnitine, which is essential for fatty acid transport into mitochondria.
Which diseases are associated with hydroxytrimethyllysine aldolase deficiency?
Deficiency can lead to carnitine deficiency disorders, characterized by cardiomyopathy, skeletal myopathy, and hypoglycemia.
How can I study hydroxytrimethyllysine aldolase activity in the lab?
You can use enzymatic assays, metabolomics, and CRISPR knockout models to measure activity and pathway flux [1,2].
Is hydroxytrimethyllysine aldolase conserved across species?
Yes, the activity has been found in humans, mice, and Candida albicans, indicating evolutionary conservation [1,2].
What are the substrates and products of hydroxytrimethyllysine aldolase?
The substrate is (3S)-3-hydroxy-N(6),N(6),N(6)-trimethyl-L-lysine; the products are 4-(trimethylamino)butanal and glycine.
What methods are used to measure hydroxytrimethyllysine aldolase activity?
Enzyme assays coupled with HPLC or mass spectrometry are commonly used to detect product formation.
Can CRISPR be used to create models for hydroxytrimethyllysine aldolase research?
Yes, CRISPR knockout, point mutation, knock-in, and overexpression models can be generated to study gene function.
Where can I find the official definition of GO:0120567?
The official definition is available in the Gene Ontology database (QuickGO) and is based on the catalytic reaction.
Conclusion
Hydroxytrimethyllysine aldolase activity (GO:0120567) is a critical enzymatic step in carnitine biosynthesis, with implications for mitochondrial fatty acid oxidation and metabolic health. The recent identification of the responsible gene in humans and mice has opened new research directions, while the fungal homolog provides a comparative model. Understanding this activity through CRISPR-based models and biochemical assays will advance our knowledge of carnitine-related disorders and potential therapeutic targets.
References
- 1. Malatesta M et al.. 2024. One substrate many enzymes virtual screening uncovers missing genes of carnitine biosynthesis in human and mouse.. Nat Commun 15(1):3199 PMID: 38615009
- 2. Strijbis K et al.. 2009. Identification and characterization of a complete carnitine biosynthesis pathway in Candida albicans.. FASEB J 23(8):2349-59 PMID: 19289605
