GO:0004819 glutamine-tRNA ligase activity: Mechanism, Genes and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0004819 glutamine-tRNA ligase activity (GlnRS) catalyzes the ATP-dependent attachment of L-glutamine to tRNA(Gln), forming Gln-tRNA(Gln) for ribosomal protein synthesis.
• GlnRS is a class I aminoacyl-tRNA synthetase that must discriminate glutamine from glutamate and other amino acids, a process governed by specific active-site residues and tRNA identity elements.
• In eukaryotes, mitochondrial and cytosolic GlnRS systems differ, and organellar glutamine codon translation can involve indirect pathways requiring transamidation.
• Human glutaminyl-tRNA synthetase (QARS) has a non-canonical antiapoptotic role by interacting with ASK1 in a glutamine-dependent manner, linking translation to cell survival signaling.
• Gln4, the yeast/fungal glutamine-tRNA synthetase, is a validated antifungal target; allosteric inhibitors of Gln4 show selective antifungal activity.
• Circadian clock control of tRNA synthetases, including glutamine-tRNA ligase, has been observed in Neurospora crassa, suggesting temporal regulation of translation.
Description
Glutamine-tRNA ligase activity (GO:0004819) is a molecular function that ensures the correct amino acid, L-glutamine, is attached to its cognate transfer RNA (tRNA(Gln)) before it is delivered to the ribosome for protein synthesis. This reaction is essential for translating the genetic code, as errors in aminoacylation can lead to mistranslation and proteotoxic stress. The enzyme responsible, glutaminyl-tRNA synthetase (GlnRS), belongs to the class I aminoacyl-tRNA synthetases and uses ATP to activate glutamine and ligate it to the 3' end of tRNA(Gln). Because glutamine is structurally similar to glutamate, GlnRS must precisely discriminate between these amino acids to maintain translational fidelity. In eukaryotic cells, glutamine-tRNA ligase activity is found in both the cytosol and mitochondria, and in some organelles or organisms, glutamine-tRNA(Gln) can be synthesized indirectly via a transamidation pathway involving a nondiscriminating glutamyl-tRNA synthetase. Beyond its canonical role, human GlnRS (encoded by QARS) interacts with apoptosis signal-regulating kinase 1 (ASK1) in a glutamine-dependent manner, conferring antiapoptotic activity and linking translation to cell survival. In fungi, the essential GlnRS ortholog Gln4 is a target for antifungal development, with allosteric inhibitors showing selective activity. Circadian clock control of tRNA synthetases in Neurospora crassa further highlights that glutamine-tRNA ligase activity is subject to temporal regulation. These features make GO:0004819 a critical node at the interface of translation, metabolism, stress signaling, and infectious disease research.
glutamine-tRNA ligase activity At A Glance
| GO ID | GO:0004819 |
|---|---|
| GO term | glutamine-tRNA ligase activity |
| Ontology | molecular_function |
| Synonym | GlnRS; glutamine translase activity; glutamine-tRNA synthetase activity; glutaminyl-transfer RNA synthetase activity; glutaminyl-tRNA synthetase activity; L-glutamine:tRNAGln ligase (AMP-forming) |
| Major function | ATP-dependent ligation of L-glutamine to tRNA(Gln), forming Gln-tRNA(Gln) for ribosomal translation |
| Reaction | ATP + L-glutamine + tRNA(Gln) = AMP + diphosphate + L-glutaminyl-tRNA(Gln) |
| Enzyme class | Class I aminoacyl-tRNA synthetase |
| Subcellular context | Cytosol and mitochondria in eukaryotes; indirect transamidation pathway in some organelles |
| Non-canonical role | Human QARS interacts with ASK1 to suppress apoptosis in a glutamine-dependent manner |
What Is GO:0004819?
GO:0004819 glutamine-tRNA ligase activity is defined as the catalysis of the reaction: ATP + L-glutamine + tRNA(Gln) = AMP + diphosphate + L-glutaminyl-tRNA(Gln). In other words, it is the enzymatic activity that charges tRNA(Gln) with glutamine, using ATP as an energy source and releasing AMP and diphosphate. This activity is also known as glutaminyl-tRNA synthetase (GlnRS) activity, glutamine translase activity, and glutaminyl-transfer RNA synthetase activity.
Why Is glutamine-tRNA ligase activity Important in Cell Biology?
Glutamine-tRNA ligase activity is fundamental to protein synthesis because it ensures that glutamine is correctly incorporated at glutamine codons, preventing mistranslation that could disrupt proteostasis. Its importance extends beyond translation: in humans, the enzyme QARS has an antiapoptotic function through ASK1 interaction, linking aminoacylation to cell survival signaling. In pathogenic fungi, Gln4 is essential and can be selectively inhibited, making it a promising antifungal target. Moreover, organellar glutamine codon translation can proceed via indirect pathways, revealing evolutionary adaptations in aminoacyl-tRNA synthesis. Circadian regulation of tRNA synthetases in Neurospora crassa suggests that glutamine-tRNA ligase activity is temporally controlled, with implications for rhythmic biology. Thus, GO:0004819 is relevant to basic translation research, cancer biology, infectious disease, and chronobiology.
• Ensures translational fidelity by correctly pairing glutamine with tRNA(Gln).
• Prevents mistranslation and proteotoxic stress by discriminating glutamine from glutamate.
• Supports mitochondrial and cytosolic protein synthesis in eukaryotes.
• Human QARS modulates apoptosis via ASK1 interaction, linking translation to cell survival.
• Fungal Gln4 is a validated antifungal target with allosteric inhibitors.
• Circadian clock control of tRNA synthetases affects temporal translation in Neurospora.
• Indirect transamidation pathways for Gln-tRNA(Gln) formation expand metabolic flexibility.
• Mutations in tRNA identity elements can alter codon translation, as shown for tRNA(2Gln) mutants.
Molecular Mechanism of glutamine-tRNA ligase activity
Substrate recognition and discrimination
In simple terms: The enzyme must pick the right amino acid (glutamine) and the right tRNA (tRNA(Gln)) from a crowded cellular pool.
Glutaminyl-tRNA synthetase (GlnRS) specifically recognizes L-glutamine and tRNA(Gln) through a set of active-site residues and tRNA identity elements. Structural and biochemical studies have shown that GlnRS uses a conserved aspartate residue to discriminate glutamine from glutamate, and mutations in this residue can relax specificity. Substrate selection by aminoacyl-tRNA synthetases is a general challenge, and GlnRS exemplifies how enzymes achieve high fidelity. In Escherichia coli, tRNA(2Gln) mutants can translate the CGA arginine codon as glutamine, demonstrating that tRNA identity elements are critical for correct codon assignment.
Catalytic mechanism: two-step aminoacylation
In simple terms: The enzyme first activates glutamine with ATP, then transfers it to the tRNA.
The reaction catalyzed by GlnRS proceeds in two steps: first, glutamine is activated by ATP to form glutaminyl-AMP (Gln-AMP) with the release of diphosphate; second, the glutaminyl group is transferred to the 3'-OH of the terminal adenosine of tRNA(Gln), releasing AMP. This two-step mechanism is characteristic of class I aminoacyl-tRNA synthetases, which adopt a Rossmann-fold catalytic domain. The overall reaction is: ATP + L-glutamine + tRNA(Gln) = AMP + diphosphate + L-glutaminyl-tRNA(Gln).
Indirect pathway and organellar translation
In simple terms: Some organelles or organisms make Gln-tRNA(Gln) indirectly by first attaching glutamate and then converting it to glutamine.
In many bacteria, archaea, and organelles, glutamine-tRNA(Gln) is not formed directly by GlnRS. Instead, a nondiscriminating glutamyl-tRNA synthetase attaches glutamate to tRNA(Gln), and a tRNA-dependent amidotransferase converts the glutamate to glutamine. This indirect pathway is essential in mitochondria and chloroplasts of some organisms, and its existence highlights the evolutionary flexibility of glutamine codon translation. The direct and indirect pathways can coexist, and their relative contributions vary by organism and compartment.
Non-canonical functions and regulation
In simple terms: Beyond charging tRNA, GlnRS can interact with signaling proteins and influence cell survival.
Human glutaminyl-tRNA synthetase (QARS) has a non-canonical antiapoptotic function: it interacts with apoptosis signal-regulating kinase 1 (ASK1) in a glutamine-dependent manner, inhibiting ASK1-mediated apoptosis. This interaction links aminoacylation to stress and survival signaling. Additionally, circadian clock control of tRNA synthetases, including glutamine-tRNA ligase, has been observed in Neurospora crassa, suggesting that the activity is temporally regulated. In fungi, Gln4 is essential and can be allosterically inhibited by N-pyrimidinyl-β-thiophenylacrylamides, providing a mechanism for selective antifungal action.
Key Genes Involved in GO:0004819 glutamine-tRNA ligase activity
The following genes and proteins are directly associated with glutamine-tRNA ligase activity (GO:0004819) or its regulation across species.
| Gene | Major Role | Research Relevance |
|---|---|---|
| QARS (human) | Cytosolic glutaminyl-tRNA synthetase; charges tRNA(Gln) with glutamine | Antiapoptotic interaction with ASK1; cancer and neurodegeneration models |
| QRSL1 (human) | Mitochondrial glutamyl-tRNA(Gln) amidotransferase subunit | Indirect pathway for Gln-tRNA(Gln) formation in mitochondria |
| GATB (human) | Glutamyl-tRNA(Gln) amidotransferase subunit B | Mitochondrial indirect pathway |
| GATC (human) | Glutamyl-tRNA(Gln) amidotransferase subunit C | Mitochondrial indirect pathway |
| Gln4 (Saccharomyces cerevisiae) | Glutaminyl-tRNA synthetase; essential for translation | Antifungal target; allosteric inhibition studies |
| Gln4 (Candida albicans) | Glutaminyl-tRNA synthetase | Antifungal target; selective inhibitors |
| glnS (Escherichia coli) | Glutaminyl-tRNA synthetase | Model for substrate selection and tRNA identity |
| tRNA(2Gln) (E. coli) | Suppressor tRNA that can translate CGA as glutamine | Codon reassignment and mistranslation studies |
| ASK1 (MAP3K5, human) | Apoptosis signal-regulating kinase 1 | Interacts with QARS; apoptosis regulation |
| c-Myc (human) | Transcription factor; glutamine signaling activates c-Myc | Glutamine-dependent cancer cell proliferation |
| Mcl-1 (human) | Anti-apoptotic Bcl-2 family protein | Glutamine signaling activates Mcl-1; survival |
| Neurospora crassa clock genes (frq, wc-1, wc-2) | Circadian clock components | Regulate tRNA synthetase expression including GlnRS |
| GlnRS (Thermus thermophilus) | Glutaminyl-tRNA synthetase | Structural studies of substrate discrimination |
| GlnRS (Saccharomyces cerevisiae) | Glutaminyl-tRNA synthetase | Model for eukaryotic GlnRS function |
| GlnRS (Homo sapiens mitochondrial) | Mitochondrial glutaminyl-tRNA synthetase | Mitochondrial translation |
| GluRS (nondiscriminating) | Glutamyl-tRNA synthetase that charges tRNA(Gln) with glutamate | Indirect pathway for Gln-tRNA(Gln) |
| GatA/GatB/GatC (bacterial) | Glutamyl-tRNA(Gln) amidotransferase subunits | Indirect pathway in bacteria |
| QARS1 (human) | Alternative symbol for glutaminyl-tRNA synthetase | Human genetics and disease |
How Is glutamine-tRNA ligase activity Regulated?
Glutamine-tRNA ligase activity is regulated at multiple levels. In Neurospora crassa, circadian clock components control the expression of tRNA synthetases, including glutamine-tRNA ligase, suggesting temporal regulation of translation. In humans, the activity of QARS is modulated by its interaction with ASK1, which is glutamine-dependent and affects apoptosis. Additionally, glutamine signaling can activate c-Myc and Mcl-1 to promote cancer cell proliferation and survival, indirectly influencing the demand for glutamine-tRNA charging. Allosteric inhibition of fungal Gln4 by small molecules demonstrates that enzymatic activity can be regulated by conformational changes. These examples illustrate that glutamine-tRNA ligase activity is not constitutive but subject to metabolic, signaling, and circadian control.
glutamine-tRNA ligase activity and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| QARS | Cancer cell survival via ASK1 interaction | QARS knockout or point-mutation in cancer cell lines; ASK1 binding assays |
| Gln4 (Candida albicans) | Fungal infection | Gln4 knockout in C. albicans; antifungal inhibitor testing |
| c-Myc | Glutamine-dependent cancer proliferation | c-Myc overexpression or knockout in cancer cells; glutamine deprivation |
| Mcl-1 | Apoptosis resistance in cancer | Mcl-1 knockout or overexpression; glutamine signaling |
| QRSL1/GATB/GATC | Mitochondrial translation defects | Knockout in human cell lines; mitochondrial translation assays |
Cancer: glutamine dependency and QARS-ASK1 signaling
Many cancer cells exhibit glutamine addiction, and glutamine signaling specifically activates c-Myc and Mcl-1 to facilitate proliferation and survival. Human glutaminyl-tRNA synthetase (QARS) interacts with ASK1 in a glutamine-dependent manner, suppressing apoptosis and promoting cell survival. This non-canonical function links glutamine-tRNA ligase activity to oncogenic signaling, making QARS a potential target in cancers with high glutamine demand.
Fungal infections: Gln4 as an antifungal target
The fungal glutaminyl-tRNA synthetase Gln4 is essential for translation and is a validated antifungal target. Allosteric inhibitors of Gln4, such as N-pyrimidinyl-β-thiophenylacrylamides, exert highly selective antifungal activity against pathogenic fungi. This highlights the potential of targeting glutamine-tRNA ligase activity to combat fungal infections.
Mitochondrial translation and organellar disease
In mitochondria, glutamine-tRNA(Gln) can be synthesized via an indirect transamidation pathway involving glutamyl-tRNA synthetase and amidotransferase subunits. Defects in this pathway could impair mitochondrial translation, though specific human diseases linked to these components require further study.
Circadian rhythm and metabolic disorders
Circadian clock control of tRNA synthetases, including glutamine-tRNA ligase, has been demonstrated in Neurospora crassa. Disruption of circadian regulation may affect translation timing and metabolic homeostasis, suggesting a link between glutamine-tRNA ligase activity and circadian-related disorders.
From glutamine-tRNA ligase activity-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| Does QARS knockout impair cell viability? | CRISPR knockout of QARS in human cancer cell lines |
| Does a specific QARS point mutation disrupt ASK1 binding? | Point-mutation knock-in of QARS at the ASK1 interaction interface |
| Can Gln4 inhibitors selectively kill fungi? | Gln4 knockout or point-mutation in Candida albicans; inhibitor treatment |
| How does glutamine-tRNA ligase activity affect circadian translation? | Knockout or tagged knock-in of GlnRS in Neurospora crassa |
| Does overexpression of QARS protect against apoptosis? | Overexpression of QARS in mammalian cells; ASK1-induced apoptosis |
| What is the role of indirect Gln-tRNA(Gln) pathway in mitochondria? | Knockout of QRSL1 or GATB in human cells; mitochondrial translation assays |
How to Study the glutamine-tRNA ligase activity Process
| Method | What It Measures | Typical Application |
|---|---|---|
| Aminoacylation assay | Enzymatic charging of tRNA(Gln) with glutamine | Kinetic analysis of GlnRS mutants |
| X-ray crystallography | Three-dimensional structure of GlnRS-tRNA complex | Substrate discrimination and inhibitor design |
| Ribo-seq | Global translation and codon occupancy | Effects of GlnRS knockout on translation |
| RNA-seq | Transcriptional changes | Glutamine signaling and c-Myc/Mcl-1 targets |
| Co-immunoprecipitation | Protein-protein interactions | QARS-ASK1 interaction |
| CRISPR knockout | Loss-of-function phenotypes | Essentiality of QARS or Gln4 |
| Site-directed mutagenesis | Specific residue function | Glutamine discrimination by GlnRS |
| Circadian reporter assays | Rhythmic expression of tRNA synthetases | Clock control in Neurospora |
Aminoacylation assays
In vitro aminoacylation assays measure the incorporation of radiolabeled glutamine into tRNA(Gln) by glutaminyl-tRNA synthetase. These assays are used to determine kinetic parameters, substrate specificity, and the effects of mutations in either the enzyme or tRNA.
Structural biology (X-ray crystallography and cryo-EM)
Structures of GlnRS in complex with tRNA(Gln) and ATP analogs have revealed the molecular basis for glutamine discrimination and tRNA recognition. Such studies guide the design of inhibitors and the interpretation of disease mutations.
Ribo-seq and RNA-seq
Ribo-seq can measure global translation and codon-specific effects when glutamine-tRNA ligase activity is perturbed. RNA-seq complements this by revealing transcriptional changes, such as those driven by c-Myc and Mcl-1 in response to glutamine signaling.
Proteomics and interactomics
Affinity purification coupled with mass spectrometry can identify interaction partners of QARS, such as ASK1, and map glutamine-dependent interactions. Proteomics can also assess mistranslation and proteotoxic stress upon GlnRS perturbation.
How CRISPR Can Be Used to Study GO:0004819 glutamine-tRNA ligase activity
Knockout
CRISPR knockout of QARS or fungal Gln4 can reveal essentiality and phenotypic consequences. For example, Gln4 knockout in Candida albicans is expected to be lethal, validating it as an antifungal target. In human cells, QARS knockout can test dependence on glutamine-tRNA ligase activity for survival and proliferation.
Point Mutation
Point mutations in QARS can dissect specific functions, such as glutamine discrimination or ASK1 binding. For instance, mutating the aspartate residue involved in substrate selection can alter amino acid specificity. Point mutations in tRNA(Gln) identity elements can also be introduced to study codon reassignment.
Knock-in
Knock-in of tagged QARS (e.g., FLAG or GFP) allows for localization, interaction, and stability studies. Tagged knock-in can be used to monitor QARS-ASK1 interaction dynamics under glutamine deprivation. Knock-in of disease-associated mutations can model their effects on translation and apoptosis.
Overexpression
Overexpression of QARS can test its antiapoptotic function and its ability to protect cells from ASK1-mediated apoptosis. Overexpression of Gln4 in fungi can assess inhibitor resistance and fitness costs. Overexpression of c-Myc or Mcl-1 can mimic glutamine signaling effects.
How EDITGENE Supports glutamine-tRNA ligase activity Research
Researchers studying glutamine-tRNA ligase activity-related genes often need to determine whether a candidate gene is causally involved in translation, cell survival, or antifungal response. EDITGENE provides a comprehensive suite of CRISPR services to enable such investigations, from knockout to precise point mutations and library screening.
Contact EDITGENE today to design your custom CRISPR model for glutamine-tRNA ligase activity research.
Frequently Asked Questions About glutamine-tRNA ligase activity
What is glutamine-tRNA ligase activity?
Glutamine-tRNA ligase activity (GO:0004819) is the enzymatic activity that attaches L-glutamine to tRNA(Gln) using ATP, forming Gln-tRNA(Gln) for protein synthesis.
What genes are involved in glutamine-tRNA ligase activity?
Key genes include QARS in humans, Gln4 in fungi, and glnS in Escherichia coli, as well as indirect pathway genes like QRSL1, GATB, and GATC.
What is the reaction catalyzed by glutamine-tRNA ligase?
The reaction is: ATP + L-glutamine + tRNA(Gln) = AMP + diphosphate + L-glutaminyl-tRNA(Gln).
How does GlnRS discriminate glutamine from glutamate?
GlnRS uses specific active-site residues, including a conserved aspartate, to selectively bind glutamine and avoid glutamate misactivation.
What is the role of QARS in apoptosis?
Human QARS interacts with ASK1 in a glutamine-dependent manner to suppress apoptosis, linking translation to cell survival.
Is glutamine-tRNA ligase a drug target?
Yes, fungal Gln4 is a validated antifungal target, and allosteric inhibitors show selective antifungal activity.
How is glutamine-tRNA ligase activity regulated?
It is regulated by circadian clock components in Neurospora, by ASK1 interaction in humans, and by allosteric inhibitors in fungi.
What is the indirect pathway for Gln-tRNA(Gln) formation?
In some organisms and organelles, glutamate is first attached to tRNA(Gln) by a nondiscriminating GluRS and then converted to glutamine by an amidotransferase.
Can tRNA mutations affect glutamine codon translation?
Yes, tRNA(2Gln) mutants in E. coli can translate the CGA arginine codon as glutamine, showing the importance of tRNA identity elements.
What methods are used to study glutamine-tRNA ligase activity?
Common methods include aminoacylation assays, X-ray crystallography, Ribo-seq, RNA-seq, co-immunoprecipitation, and CRISPR knockout models.
Conclusion
Glutamine-tRNA ligase activity (GO:0004819) is a cornerstone of accurate protein synthesis, ensuring glutamine is correctly incorporated into nascent polypeptides. Its importance extends to cell survival signaling, antifungal drug development, and circadian biology. Understanding its mechanism, regulation, and disease connections requires robust experimental models. EDITGENE offers comprehensive CRISPR services to accelerate research on this essential molecular function.
References
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- 6. Puumala E et al.. 2024. Allosteric inhibition of tRNA synthetase Gln4 by N-pyrimidinyl-β-thiophenylacrylamides exerts highly selective antifungal activity.. Cell Chem Biol 31(4):760-775.e17 PMID: 38402621
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