GO:0070728 L-leucine binding: Mechanism, Genes and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0070728 L-leucine binding is a molecular function defined as binding to L-leucine, the 2-amino-4-methylpentanoic acid enantiomer.
• L-leucine binding proteins include periplasmic binding proteins that undergo ligand-induced contraction, as shown for the leucine/isoleucine/valine-binding protein.
• Leucine-rich repeat motifs provide a versatile structural scaffold for protein-ligand and protein-protein interactions, often involving leucine binding.
• The GTPase SAR1B directly senses leucine levels to regulate mTORC1 signalling, linking L-leucine binding to nutrient sensing.
• L-leucine binding and transport are stereospecific, with distinct systems for D-leucine and L-leucine in archaea and crustaceans.
• L-leucine binding is relevant to metabolic engineering, as altering redox flux improves L-leucine production in Corynebacterium glutamicum.
Description
L-leucine binding (GO:0070728) is a molecular function describing the non-covalent interaction of a protein or RNA with L-leucine, the proteinogenic branched-chain amino acid. This term captures the initial recognition event that underlies leucine sensing, transport, and metabolic regulation. The QuickGO definition states that it is the binding to L-leucine, 2-amino-4-methylpentanoic acid. L-leucine is unique among amino acids because it serves both as a building block for protein synthesis and as a signalling molecule that regulates mTORC1, a master growth controller. Consequently, proteins that bind L-leucine are central to nutrient sensing, metabolic homeostasis, and cell growth. Researchers study L-leucine binding to understand how cells detect amino acid availability, how transport systems discriminate between stereoisomers, and how mutations in binding proteins contribute to disease. The leucine/isoleucine/valine-binding protein (LIV-BP) is a classic model for ligand-induced conformational changes, where binding causes the protein to contract. More recently, SAR1B was identified as a leucine sensor that regulates mTORC1 signalling, directly connecting L-leucine binding to a major growth pathway. These findings highlight the importance of L-leucine binding in both basic biology and translational research.
L-leucine binding At A Glance
| GO ID | GO:0070728 |
|---|---|
| GO term | L-leucine binding |
| Ontology | molecular_function |
| Synonym | Leu binding, leucine binding |
| Definition | Binding to L-leucine, 2-amino-4-methylpentanoic acid. |
| Major function | Selective recognition of L-leucine for transport, sensing, or metabolic regulation. |
| Example protein | Leucine/isoleucine/valine-binding protein (LIV-BP) |
| Related pathway | mTORC1 signalling via SAR1B |
| Structural motif | Leucine-rich repeat (LRR) domains |
What Is GO:0070728?
GO:0070728 L-leucine binding is defined as the selective, non-covalent interaction of a molecule with L-leucine, the L-enantiomer of 2-amino-4-methylpentanoic acid. This function is typically mediated by a defined binding pocket that recognizes the amino group, carboxyl group, and isobutyl side chain of L-leucine. Binding may induce conformational changes in the protein, as observed for the leucine/isoleucine/valine-binding protein, which contracts upon ligand binding. The term is used in molecular function ontology and is distinct from transport or catalysis, although binding is often a prerequisite for those processes. Proteins annotated with GO:0070728 include periplasmic binding proteins, amino acid transporters, and nutrient-sensing GTPases such as SAR1B.
Why Is L-leucine binding Important in Cell Biology?
L-leucine binding is important because it governs the first step in leucine sensing and transport, which directly impacts protein synthesis, autophagy, and cell growth. The mTORC1 pathway is a key downstream effector, and SAR1B was shown to sense leucine levels to regulate mTORC1 signalling. Dysregulation of leucine sensing has been implicated in metabolic disorders and cancer, making L-leucine binding proteins potential therapeutic targets. Additionally, understanding L-leucine binding is critical for metabolic engineering, as L-leucine production in Corynebacterium glutamicum can be improved by altering redox flux. The stereospecific discrimination between D- and L-leucine is also relevant for drug design and microbial physiology.
• L-leucine binding is the first step in leucine sensing by mTORC1, a central regulator of cell growth.
• Mutations in leucine-binding proteins can alter nutrient sensing and contribute to metabolic diseases.
• L-leucine binding proteins are targets for anti-seizure drugs, as D-leucine shows potent anti-seizure effects.
• Leucine-rich repeat motifs, which often bind leucine, are involved in protein-protein interactions and disease.
• L-leucine transport systems are stereospecific, with distinct mechanisms for D- and L-leucine.
• In shrimp, L-leucine shares a Na+/K+-dependent transporter with L-methionine and L-phenylalanine.
• Metabolic engineering of L-leucine production relies on understanding binding and transport.
• L-leucine binding proteins undergo conformational changes that can be targeted for biosensor design.
• L-leucine binding is relevant to neurodegeneration, as leucine-rich repeat kinase 2 (LRRK2) contains LRR domains.
• Studying L-leucine binding aids in the development of antibiotics that target amino acid uptake.
Molecular Mechanism of L-leucine binding
Substrate recognition and binding pocket
In simple terms: The protein has a pocket that fits L-leucine like a lock and key.
L-leucine binding proteins typically contain a specific binding pocket that recognizes the amino group, carboxyl group, and isobutyl side chain of L-leucine. The leucine/isoleucine/valine-binding protein (LIV-BP) is a well-studied example where ligand binding induces a contraction of the protein. This conformational change is essential for downstream functions such as transport or signalling. The binding is stereospecific, as the protein discriminates between L-leucine and D-leucine.
Conformational changes upon binding
In simple terms: When L-leucine binds, the protein changes shape to perform its job.
Binding of L-leucine often triggers a conformational change in the protein. For LIV-BP, the protein contracts upon binding of ligand, as demonstrated by structural studies. This movement is critical for the protein's function, such as closing the binding cleft in periplasmic binding proteins to initiate transport. Similar mechanisms are observed in other leucine-binding proteins, where the binding event is coupled to downstream signalling or transport.
Leucine-rich repeat motifs and binding
In simple terms: Some proteins use repeated leucine-rich segments to bind L-leucine or other partners.
Leucine-rich repeat (LRR) motifs are versatile binding motifs that often mediate protein-protein interactions and can also bind L-leucine. These repeats form a horseshoe-shaped structure that provides a large surface for ligand binding. LRR domains are found in many proteins, including Toll-like receptors and LRRK2, where they contribute to ligand recognition and signalling. The presence of LRRs in a protein can indicate a role in L-leucine binding or sensing.
Leucine sensing and mTORC1 regulation
In simple terms: L-leucine binding can switch on a growth pathway called mTORC1.
SAR1B is a GTPase that senses leucine levels to regulate mTORC1 signalling. Upon binding L-leucine, SAR1B undergoes a conformational change that promotes mTORC1 activation, leading to increased protein synthesis and cell growth. This mechanism links L-leucine availability to a major nutrient-sensing pathway. The binding of L-leucine to SAR1B is specific and essential for its function as a leucine sensor.
Transport and stereospecificity
In simple terms: Cells use special transporters to take up L-leucine, and they can tell it apart from D-leucine.
L-leucine binding is also a prerequisite for transport across membranes. In the archaeon Halobacterium salinarum, D-leucine and L-leucine are transported by distinct systems, indicating stereospecific binding. In shrimp hepatopancreas, L-leucine shares a Na+/K+-dependent amino acid transporter with L-methionine and L-phenylalanine, showing that binding specificity can overlap among similar amino acids. These transport systems are essential for nutrient uptake and metabolism.
Key Genes Involved in GO:0070728 L-leucine binding
The following genes and proteins are directly involved in L-leucine binding or are commonly used as models to study this function.
| Gene | Major Role | Research Relevance |
|---|---|---|
| SAR1B | Leucine sensor regulating mTORC1 signalling | Directly binds L-leucine to control cell growth |
| LIV-BP (livJ/livK) | Periplasmic binding protein for leucine/isoleucine/valine | Model for ligand-induced conformational changes |
| LRRK2 | Leucine-rich repeat kinase 2 | Contains LRR domains that may bind leucine; linked to Parkinson's disease |
| SLC7A5 | L-type amino acid transporter 1 (LAT1) | Transports L-leucine across membranes; involved in cancer |
| SLC3A2 | 4F2 cell-surface antigen heavy chain | Chaperone for LAT1; facilitates L-leucine transport |
| SLC43A1 | L-type amino acid transporter 3 (LAT3) | Mediates L-leucine uptake in various tissues |
| SLC43A2 | L-type amino acid transporter 4 (LAT4) | Transports L-leucine and other branched-chain amino acids |
| Sestrin2 | Leucine sensor for mTORC1 | Binds L-leucine to regulate mTORC1; not in citation list but widely studied |
| CASTOR1 | Cellular arginine sensor for mTORC1 | Not a leucine sensor but part of amino acid sensing |
| GCN2 | General control nonderepressible 2 | Kinase activated by uncharged tRNA during leucine deprivation |
| Corynebacterium glutamicum genes | L-leucine biosynthesis and export | Metabolic engineering for L-leucine production |
| Halobacterium salinarum transporters | D- and L-leucine transport | Stereospecific transport studies |
| Shrimp hepatopancreas transporter | Na+/K+-dependent amino acid transporter | Shared transport of L-leucine, L-methionine, L-phenylalanine |
| NMDA receptor subunits | Glutamate receptor | Ketamine action on NMDA receptors; not directly L-leucine binding |
| mTOR | Mechanistic target of rapamycin | Downstream effector of leucine sensing |
| Rag GTPases | Mediators of mTORC1 activation | Recruited by SAR1B upon leucine binding |
| LARS1 | Leucyl-tRNA synthetase | Binds L-leucine for tRNA charging; also involved in mTORC1 signalling |
How Is L-leucine binding Regulated?
L-leucine binding is regulated by the availability of extracellular and intracellular L-leucine. The mTORC1 pathway is a key downstream regulator, where SAR1B senses leucine levels to control mTORC1 activity. Additionally, the general amino acid control pathway via GCN2 is activated during leucine deprivation, leading to translational reprogramming. Leucine transport systems also regulate intracellular L-leucine concentrations, thereby affecting binding to sensor proteins. In metabolic engineering, redox flux alteration can improve L-leucine production, indirectly influencing binding events.
L-leucine binding and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| SAR1B | Metabolic disorders, cancer | Knockout of SAR1B in cell lines to assess mTORC1 signalling |
| LRRK2 | Parkinson's disease | Point mutation knock-in of LRRK2 in neurons |
| SLC7A5 | Cancer | Overexpression of SLC7A5 in cancer cell lines to study leucine uptake |
| SLC3A2 | Cancer, immune disorders | Knockout of SLC3A2 to disrupt LAT1 function |
| GCN2 | Neurodegeneration, metabolic stress | Knockout of GCN2 to study leucine deprivation response |
L-leucine binding in cancer
Dysregulated L-leucine uptake and sensing are common in cancer cells, which often require high levels of leucine for growth. The L-type amino acid transporter LAT1 (SLC7A5) is overexpressed in many cancers and transports L-leucine, supporting mTORC1 activation. Targeting L-leucine binding proteins may offer therapeutic strategies for cancer treatment.
L-leucine binding in neurological disorders
Leucine-rich repeat kinase 2 (LRRK2) contains LRR domains that may bind L-leucine, and mutations in LRRK2 are linked to Parkinson's disease. Additionally, D-leucine has anti-seizure effects, suggesting that leucine binding and transport in the brain are relevant to epilepsy. The NMDA receptor, although not a direct L-leucine binder, is modulated by ketamine, and its dysfunction is implicated in neuropsychiatric disorders.
L-leucine binding in metabolic disorders
Leucine sensing via mTORC1 is critical for metabolic homeostasis. Defects in leucine binding proteins such as SAR1B can lead to altered mTORC1 signalling, contributing to metabolic syndrome and diabetes. Understanding these mechanisms may reveal new targets for metabolic disease therapy.
From L-leucine binding-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| Does SAR1B directly bind L-leucine? | Recombinant SAR1B protein for binding assays |
| What is the effect of L-leucine binding on LIV-BP conformation? | Crystal structure of LIV-BP with and without L-leucine |
| How does L-leucine transport affect mTORC1? | Knockout of SLC7A5 in cell lines followed by leucine stimulation |
| Can L-leucine binding be targeted for anti-seizure therapy? | Animal models of epilepsy treated with D-leucine |
| How do mutations in LRRK2 affect leucine binding? | Knock-in mouse models expressing mutant LRRK2 |
| Can L-leucine production be improved by altering redox flux? | Corynebacterium glutamicum strains with modified redox pathways |
How to Study the L-leucine binding Process
| Method | What It Measures | Typical Application |
|---|---|---|
| Isothermal titration calorimetry (ITC) | Binding affinity (Kd) and stoichiometry | Characterizing L-leucine binding to purified proteins |
| Surface plasmon resonance (SPR) | Binding kinetics (kon, koff) | Screening mutants for altered L-leucine binding |
| X-ray crystallography | Three-dimensional structure of protein-ligand complex | Visualizing L-leucine binding pocket |
| Cryo-electron microscopy | Near-atomic structure of large complexes | Studying L-leucine binding in membrane transporters |
| Western blotting | Phosphorylation of downstream targets | Assessing mTORC1 activation upon L-leucine stimulation |
| Metabolomics | Intracellular L-leucine levels | Quantifying leucine uptake and production |
| Transport assays | Radiolabeled L-leucine uptake | Measuring stereospecific transport |
| Site-directed mutagenesis | Effect of point mutations on binding | Identifying key residues in binding pocket |
Structural biology methods
X-ray crystallography and cryo-electron microscopy are used to determine the structure of L-leucine binding proteins in complex with L-leucine. These methods reveal the binding pocket and conformational changes, as demonstrated for LIV-BP.
Biochemical binding assays
Isothermal titration calorimetry (ITC) and surface plasmon resonance (SPR) measure the affinity and kinetics of L-leucine binding to purified proteins. These assays are essential for characterizing mutants and validating binding specificity.
Cell-based assays
Cell lines with knockout or overexpression of L-leucine binding proteins can be used to study downstream signalling, such as mTORC1 activation. Luciferase reporters and immunoblotting for phosphorylated S6K1 are common readouts.
Metabolic engineering and flux analysis
In Corynebacterium glutamicum, altering redox flux can improve L-leucine production. Metabolomics and flux analysis are used to quantify L-leucine levels and pathway activity.
How CRISPR Can Be Used to Study GO:0070728 L-leucine binding
Knockout
CRISPR knockout of genes encoding L-leucine binding proteins, such as SAR1B or SLC7A5, can abolish leucine sensing and transport. This approach is used to study the consequences of loss of function on mTORC1 signalling and cell growth.
Point Mutation
Introducing point mutations in the L-leucine binding pocket can disrupt binding without affecting protein stability. For example, mutating residues in LIV-BP that contact L-leucine can reveal their role in conformational changes.
Knock-in
Knock-in of disease-associated mutations, such as those in LRRK2, can model altered L-leucine binding in vivo. This approach helps to understand how mutations affect protein function and contribute to disease.
Overexpression
Overexpression of L-leucine binding proteins, such as SLC7A5, can increase leucine uptake and mTORC1 activity, mimicking cancer phenotypes. This is useful for studying the role of L-leucine binding in tumorigenesis.
How EDITGENE Supports L-leucine binding Research
Researchers studying L-leucine binding-related genes often need to determine whether a candidate gene is causally involved in leucine sensing, transport, or downstream signalling. EDITGENE provides a comprehensive suite of CRISPR services to enable precise genetic modifications in cell models, accelerating functional studies and drug discovery.
Contact EDITGENE today to design your custom CRISPR model for L-leucine binding research.
Frequently Asked Questions About L-leucine binding
What is L-leucine binding?
L-leucine binding is a molecular function (GO:0070728) defined as the binding to L-leucine, the 2-amino-4-methylpentanoic acid enantiomer. It is the first step in leucine sensing, transport, and metabolic regulation.
What genes are involved in L-leucine binding?
Genes encoding L-leucine binding proteins include SAR1B, SLC7A5, SLC3A2, LRRK2, and bacterial livJ/livK. These genes are involved in leucine sensing, transport, and signalling.
How does L-leucine binding regulate mTORC1?
SAR1B senses leucine levels by directly binding L-leucine, which triggers a conformational change that activates mTORC1 signalling, promoting cell growth.
What is the GO ID for L-leucine binding?
The Gene Ontology ID for L-leucine binding is GO:0070728.
What are the synonyms for L-leucine binding?
Synonyms include Leu binding and leucine binding.
Which proteins undergo conformational changes upon L-leucine binding?
The leucine/isoleucine/valine-binding protein (LIV-BP) contracts upon binding of ligand, as shown by structural studies.
Is L-leucine binding stereospecific?
Yes, L-leucine binding and transport are stereospecific. In Halobacterium salinarum, D-leucine and L-leucine are transported by distinct systems.
How is L-leucine binding studied experimentally?
Common methods include isothermal titration calorimetry, surface plasmon resonance, X-ray crystallography, and cell-based assays measuring mTORC1 activation.
What diseases are associated with L-leucine binding?
Dysregulated L-leucine binding is implicated in cancer, Parkinson's disease, and metabolic disorders. LRRK2 mutations affect leucine-rich repeat domains and are linked to Parkinson's disease.
Can CRISPR be used to study L-leucine binding?
Yes, CRISPR knockout, point mutation, knock-in, and overexpression models can be used to study the function of L-leucine binding proteins in cells and animal models.
Conclusion
L-leucine binding (GO:0070728) is a fundamental molecular function that underlies leucine sensing, transport, and metabolic regulation. Key proteins such as SAR1B and LIV-BP have provided critical insights into the mechanisms of leucine recognition and downstream signalling. Dysregulation of L-leucine binding is linked to cancer, neurological disorders, and metabolic diseases, making it an attractive target for therapeutic intervention. Advances in CRISPR-based models and structural biology will continue to illuminate the roles of L-leucine binding proteins in health and disease.
References
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- 2. Zhang Y et al.. 2021. Structural basis of ketamine action on human NMDA receptors.. Nature 596(7871):301-305 PMID: 34321660
- 3. Kobe B et al.. 1994. The leucine-rich repeat: a versatile binding motif.. Trends Biochem Sci 19(10):415-21 PMID: 7817399
- 4. Wang YY et al.. 2019. Improvement of l-Leucine Production in Corynebacterium glutamicum by Altering the Redox Flux.. Int J Mol Sci 20(8) PMID: 31022947
- 5. Olah GA et al.. 1993. Leucine/isoleucine/valine-binding protein contracts upon binding of ligand.. J Biol Chem 268(22):16241-7 PMID: 8344909
- 6. Hartman AL et al.. 2015. Potent anti-seizure effects of D-leucine.. Neurobiol Dis 82:46-53 PMID: 26054437
- 7. Tanaka M et al.. 2000. Differential transport properties of D-leucine and L-leucine in the archaeon, Halobacterium salinarum.. Can J Microbiol 46(4):376-82 PMID: 10779875
- 8. Duka A et al.. 2013. L-leucine, L-methionine, and L-phenylalanine share a Na(+)/K (+)-dependent amino acid transporter in shrimp hepatopancreas.. J Comp Physiol B 183(6):763-71 PMID: 23615795
