GO:0098619 selenocysteine-tRNA ligase activity: Mechanism, Genes and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0098619 selenocysteine-tRNA ligase activity catalyzes the ATP-dependent attachment of L-serine to tRNASec, producing Ser-tRNASec, AMP, and diphosphate.
• In bacteria, the same seryl-tRNA synthetase (SerRS) aminoacylates both tRNASer and tRNASec, but tRNA identity elements differ, especially the long extra arm.
• In eukaryotes and archaea, the pathway is indirect: SerRS first charges tRNASec with serine, then SepSecS converts Ser-tRNASec to selenocysteinyl-tRNASec.
• The unique long aminoacyl acceptor stem of tRNASec is required for efficient serylation and subsequent selenocysteylation in eukaryotes.
• Structural and biochemical studies show substrate promiscuity and asymmetry in the terminal catalytic complex, explaining how SerRS recognizes tRNASec.
• Dysregulation of selenocysteine-tRNA ligase activity can impair selenoprotein synthesis, affecting redox homeostasis, cancer, and neurodegeneration.
Description
GO:0098619 selenocysteine-tRNA ligase activity is a molecular function that catalyzes the reaction: tRNASec + L-Ser + ATP = Ser-tRNASec + AMP + diphosphate. This activity is the first committed step in selenocysteine (Sec) biosynthesis, a process essential for the production of selenoproteins that contain the 21st amino acid, selenocysteine. In bacteria, the same seryl-tRNA synthetase (SerRS) directly aminoacylates both tRNASer and tRNASec, whereas in eukaryotes and archaea, SerRS charges tRNASec with serine, and a separate enzyme, SepSecS, subsequently converts Ser-tRNASec to selenocysteinyl-tRNASec. The dual identity of tRNASec for SerRS and downstream enzymes is a paradigm for tRNA recognition and amino acid modification. Researchers study this activity to understand translational fidelity, selenium metabolism, and the molecular basis of diseases linked to selenoprotein dysfunction.
selenocysteine-tRNA ligase activity At A Glance
| GO ID | GO:0098619 |
|---|---|
| GO term | selenocysteine-tRNA ligase activity |
| Ontology | molecular_function |
| Synonym | None |
| Definition | Catalysis of the reaction: tRNASec + L-Ser + ATP = Ser-tRNASec + AMP + diphosphate |
| Major function | Aminoacylation of tRNASec with serine, the first step in selenocysteine biosynthesis |
| Enzyme class | Ligase (aminoacyl-tRNA synthetase) |
| Substrates | tRNASec, L-serine, ATP |
| Products | Ser-tRNASec, AMP, diphosphate |
| Related activity | Seryl-tRNA synthetase (SerRS) activity; selenocysteine synthase (SepSecS) activity |
What Is GO:0098619?
According to the Gene Ontology, GO:0098619 selenocysteine-tRNA ligase activity is defined as the catalysis of the reaction: tRNASec + L-Ser + ATP = Ser-tRNASec + AMP + diphosphate. In other words, it is the enzyme activity that attaches the amino acid serine to the specialized transfer RNA that will ultimately carry selenocysteine (tRNASec), using ATP as an energy source and releasing AMP and diphosphate. This activity is distinct from the subsequent conversion of Ser-tRNASec to selenocysteinyl-tRNASec, which is catalyzed by selenocysteine synthase (SepSecS) in eukaryotes and archaea.
Why Is selenocysteine-tRNA ligase activity Important in Cell Biology?
GO:0098619 selenocysteine-tRNA ligase activity is critical because it initiates the pathway that produces selenocysteinyl-tRNASec, the aminoacyl-tRNA used to incorporate selenocysteine into selenoproteins. Selenoproteins are essential for antioxidant defense, thyroid hormone metabolism, and redox signaling, and their dysfunction is linked to cancer, cardiovascular disease, and neurodegeneration. Understanding this activity at the molecular level informs efforts to modulate selenoprotein expression for therapeutic benefit and to interpret genetic variants that affect tRNA charging.
• Initiates selenocysteine biosynthesis, a prerequisite for selenoprotein production.
• Determines translational fidelity by ensuring correct aminoacylation of tRNASec.
• Explains the dual identity of tRNASec for SerRS and SepSecS in eukaryotes.
• Provides a model for tRNA recognition and substrate promiscuity in aminoacyl-tRNA synthetases.
• Links to redox homeostasis and antioxidant defense through selenoproteins.
• Relevant to cancer biology, as altered selenoprotein expression affects tumor progression.
• Implicated in neurodegeneration and aging via oxidative stress.
• Target for engineering improved serylation of tRNASec in synthetic biology.
• Helps interpret genetic variants in tRNA genes and synthetases.
• Guides development of inhibitors or modulators of selenoprotein synthesis.
Molecular Mechanism of selenocysteine-tRNA ligase activity
Substrate Recognition and Binding
In simple terms: The enzyme first grabs the tRNA and the amino acid serine.
Seryl-tRNA synthetase (SerRS) recognizes tRNASec through specific identity elements, including the long extra arm and the acceptor stem. In bacteria, the same SerRS aminoacylates both tRNASer and tRNASec, but the long extra arm of tRNASec contributes to its distinct identity. In eukaryotes, the uniquely long aminoacyl acceptor stem of tRNASec is necessary for efficient serylation. Structural studies of bacterial tRNASec reveal a tertiary fold that positions the acceptor end for catalysis.
Aminoacylation Catalysis
In simple terms: The enzyme attaches serine to the tRNA using ATP energy.
The catalytic reaction follows the two-step aminoacyl-tRNA synthetase mechanism: ATP and serine form seryl-AMP, releasing diphosphate, and the seryl group is then transferred to the 3' end of tRNASec, releasing AMP. This produces Ser-tRNASec, the product of GO:0098619. Human SerRS exhibits substrate promiscuity, allowing it to charge tRNASec despite differences from tRNASer.
Substrate Promiscuity and Specificity
In simple terms: The enzyme can handle two similar tRNAs but still distinguishes them.
Human seryl-tRNA synthetase can aminoacylate both tRNASer and tRNASec, but with different efficiencies, reflecting structural plasticity in the active site. The dual identity of mammalian tRNASec for SerRS and selenocysteine synthase ensures that the serine attached by SerRS is subsequently converted to selenocysteine. Engineering SerRS can improve serylation of tRNASec, as shown by designed variants.
Coupling to Selenocysteine Synthesis
In simple terms: After serine is attached, another enzyme turns it into selenocysteine.
In eukaryotes and archaea, Ser-tRNASec is not directly used for translation; instead, SepSecS converts the seryl moiety to selenocysteinyl-tRNASec using a pyridoxal phosphate-dependent mechanism. The human SepSecS-tRNASec complex reveals the structural basis for this conversion, which requires the unique acceptor stem of tRNASec. In bacteria, a different enzyme, SelA, performs the conversion, and the terminal catalytic complex shows structural asymmetry.
Regulation and Quality Control
In simple terms: The cell checks that the tRNA is correctly charged before using it.
Aminoacylation of tRNASec is subject to quality control by the synthetase and downstream factors to ensure translational fidelity. The long acceptor stem of tRNASec acts as a positive determinant for both serylation and selenocysteylation, coupling the two steps. Structural asymmetry in the terminal catalytic complex suggests coordinated regulation of the two tRNA molecules in the complex.
Key Genes Involved in GO:0098619 selenocysteine-tRNA ligase activity
The following genes and proteins are directly involved in selenocysteine-tRNA ligase activity and its coupled pathways.
| Gene | Major Role | Research Relevance |
|---|---|---|
| SARS1 | Seryl-tRNA synthetase 1; charges tRNASec with serine | Core enzyme for GO:0098619; target for engineering |
| SARS2 | Mitochondrial seryl-tRNA synthetase | May contribute to mitochondrial selenoprotein synthesis |
| SEPSECS | Selenocysteine synthase; converts Ser-tRNASec to Sec-tRNASec | Links GO:0098619 to selenoprotein production |
| TRNAU1AP | tRNA selenocysteine 1 associated protein 1 | Modulates tRNASec maturation and function |
| EEFSEC | Eukaryotic elongation factor, selenocysteine-tRNA specific | Delivers Sec-tRNASec to ribosome |
| SELENOP | Selenoprotein P; contains multiple selenocysteines | Readout of selenoprotein synthesis |
| GPX1 | Glutathione peroxidase 1; selenoprotein | Antioxidant enzyme dependent on Sec |
| GPX4 | Glutathione peroxidase 4; selenoprotein | Lipid peroxidation defense; ferroptosis |
| TXNRD1 | Thioredoxin reductase 1; selenoprotein | Redox regulation |
| TXNRD2 | Thioredoxin reductase 2; selenoprotein | Mitochondrial redox control |
| SELENOW | Selenoprotein W | Muscle and redox function |
| SELENOF | Selenoprotein F | ER redox homeostasis |
| SELENOK | Selenoprotein K | ER membrane protein |
| SELENOS | Selenoprotein S | ER stress response |
| SELENOT | Selenoprotein T | Redox and neuroendocrine function |
| SELENOM | Selenoprotein M | Neuronal redox regulation |
| SELENON | Selenoprotein N | Muscle development; mutations cause rigid spine syndrome |
| SELENOI | Selenoprotein I | Phospholipid synthesis |
How Is selenocysteine-tRNA ligase activity Regulated?
The activity of selenocysteine-tRNA ligase is regulated at multiple levels. In eukaryotes, the availability of tRNASec and the expression of SerRS and SepSecS influence the flux through the pathway. The unique long acceptor stem of tRNASec acts as a positive determinant for both serylation and subsequent selenocysteylation, coupling the two steps. Additionally, the structural asymmetry observed in the terminal catalytic complex suggests that the two tRNA molecules in the complex may be regulated differently. Selenium status can affect selenoprotein synthesis, indirectly impacting the demand for charged tRNASec.
selenocysteine-tRNA ligase activity and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| SEPSECS | Pontocerebellar hypoplasia; selenoprotein deficiency | Knockout in neuronal cell lines; patient-derived iPSCs |
| GPX4 | Ferroptosis; cancer; neurodegeneration | Point mutation of catalytic Sec; overexpression |
| TXNRD1 | Cancer; oxidative stress | Knockout; knock-in of tagged enzyme |
| SELENON | Rigid spine muscular dystrophy | Knock-in of patient mutations in myoblasts |
| SARS1 | Potential tRNA charging defects | Point mutation in active site; KO |
Cancer and Selenoprotein Dysregulation
Altered selenoprotein expression is associated with cancer progression, and selenocysteine-tRNA ligase activity is required for selenoprotein synthesis. Reduced selenoprotein levels can impair antioxidant defense, leading to oxidative stress and genomic instability. Targeting the selenocysteine pathway is being explored for cancer therapy.
Neurodegeneration and Oxidative Stress
Selenoproteins play critical roles in neuronal redox homeostasis, and defects in selenocysteine metabolism are linked to neurodegeneration. Impaired selenocysteine-tRNA ligase activity could reduce selenoprotein levels, increasing vulnerability to oxidative damage in neurons.
Genetic Variants and tRNA Identity
Mutations in genes encoding tRNASec or its synthetases can affect serylation efficiency and selenoprotein production. Structural studies provide a framework for interpreting such variants.
From selenocysteine-tRNA ligase activity-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| Does loss of SerRS affect selenoprotein synthesis? | CRISPR knockout of SARS1 in HEK293 or HeLa cells |
| How do point mutations in tRNASec affect serylation? | Point mutation of tRNA genes using CRISPR or minigene systems |
| Can engineered SerRS improve selenocysteine incorporation? | Knock-in of designed SerRS variants |
| Where is SerRS localized during selenocysteine synthesis? | Tagged knock-in of SARS1 with fluorescent protein |
| Does overexpression of SepSecS enhance selenoprotein production? | Overexpression of SEPSECS in mammalian cells |
| What is the impact of tRNASec levels on translation? | Overexpression or knockout of tRNA genes |
How to Study the selenocysteine-tRNA ligase activity Process
| Method | What It Measures | Typical Application |
|---|---|---|
| Aminoacylation assay | Formation of Ser-tRNASec | Enzyme kinetics of SerRS |
| X-ray crystallography | 3D structure of tRNA-protein complexes | Substrate recognition |
| Cryo-EM | Structure of large complexes | SepSecS-tRNASec complex |
| Ribo-seq | Translation efficiency of selenoprotein mRNAs | Selenoprotein synthesis |
| RNA-seq | Gene expression of pathway components | Regulation studies |
| Proteomics | Selenoprotein abundance | Pathway output |
| Radioactive selenium tracing | Selenium incorporation into proteins | Selenoprotein synthesis |
| Site-directed mutagenesis | Effect of point mutations on activity | Structure-function analysis |
Aminoacylation Assays
In vitro aminoacylation assays using purified SerRS and tRNASec measure the formation of Ser-tRNASec, directly quantifying GO:0098619 activity. These assays typically use radiolabeled serine and acid-precipitation to detect charged tRNA.
Structural Biology
X-ray crystallography and cryo-EM have revealed the structures of bacterial tRNASec and the human SepSecS-tRNASec complex, providing mechanistic insights into substrate recognition and catalysis. Structural asymmetry in the terminal catalytic complex has been observed.
Ribo-seq and RNA-seq
Ribosome profiling can monitor translation of selenoprotein mRNAs, which depends on charged Sec-tRNASec. RNA-seq can assess expression of genes involved in the pathway.
Proteomics and Selenium Tracing
Mass spectrometry-based proteomics can detect selenoproteins and their selenocysteine content, reflecting pathway activity. Selenium tracing using radioactive isotopes can follow incorporation.
How CRISPR Can Be Used to Study GO:0098619 selenocysteine-tRNA ligase activity
Knockout
CRISPR knockout of SARS1 or SEPSECS can abolish selenocysteine-tRNA ligase activity and selenoprotein synthesis, providing a clean background to study pathway requirements. Knockout cell lines are useful for rescue experiments with wild-type or mutant enzymes.
Point Mutation
Introducing point mutations into the active site of SerRS or into tRNASec can dissect the contribution of specific residues to serylation efficiency. Such models help interpret patient variants.
Knock-in
Knock-in of tagged SerRS or SepSecS allows live-cell imaging and proteomic analysis of the pathway. Knock-in of engineered SerRS variants can improve selenocysteine incorporation.
Overexpression
Overexpression of SARS1 or SEPSECS can enhance selenoprotein production and is used to study pathway flux. Overexpression of tRNASec can also boost selenocysteine incorporation.
How EDITGENE Supports selenocysteine-tRNA ligase activity Research
Researchers studying selenocysteine-tRNA ligase activity-related genes often need to determine whether a candidate gene is causally involved in selenoprotein synthesis, tRNA charging, or disease phenotypes. EDITGENE provides comprehensive CRISPR-based services to create precisely engineered cell models for such investigations.
Contact EDITGENE today to design your custom CRISPR model for selenocysteine-tRNA ligase activity research.
Frequently Asked Questions About selenocysteine-tRNA ligase activity
What is selenocysteine-tRNA ligase activity?
It is the enzyme activity that attaches serine to tRNASec, forming Ser-tRNASec, as defined by GO:0098619.
What genes are involved in selenocysteine-tRNA ligase activity?
Key genes include SARS1 (seryl-tRNA synthetase), SEPSECS (selenocysteine synthase), and tRNA genes for tRNASec.
What is the reaction catalyzed by GO:0098619?
tRNASec + L-Ser + ATP = Ser-tRNASec + AMP + diphosphate.
How is selenocysteine-tRNA ligase activity different in bacteria and eukaryotes?
In bacteria, SerRS directly charges tRNASec; in eukaryotes, SerRS charges tRNASec with serine, then SepSecS converts it to selenocysteine.
Why is the long extra arm of tRNASec important?
The long extra arm contributes to tRNA identity and is required for efficient serylation and selenocysteylation.
What diseases are linked to defects in this pathway?
Cancer, neurodegeneration, and muscular dystrophy have been associated with selenoprotein dysfunction.
How can I study selenocysteine-tRNA ligase activity in the lab?
Aminoacylation assays, structural biology, Ribo-seq, and proteomics are common methods.
What CRISPR models are available for this pathway?
Knockout, point mutation, knock-in, and overexpression models for SARS1, SEPSECS, and related genes.
Does human SerRS show substrate promiscuity?
Yes, human SerRS can aminoacylate both tRNASer and tRNASec with different efficiencies.
What is the role of SepSecS in selenocysteine synthesis?
SepSecS converts Ser-tRNASec to selenocysteinyl-tRNASec using pyridoxal phosphate.
Conclusion
GO:0098619 selenocysteine-tRNA ligase activity is a fundamental molecular function that initiates selenocysteine biosynthesis and ensures selenoprotein production. Its mechanism involves specific tRNA recognition, aminoacylation, and coupling to downstream conversion, with structural and biochemical studies providing detailed insights. Understanding this activity is essential for interpreting selenoprotein-related diseases and for developing targeted interventions.
References
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- 3. Ohama T et al.. 1994. Selenocysteine tRNA and serine tRNA are aminoacylated by the same synthetase, but may manifest different identities with respect to the long extra arm.. Arch Biochem Biophys 315(2):293-301 PMID: 7986071
- 4. Holman KM et al.. 2017. Insights into substrate promiscuity of human seryl-tRNA synthetase.. RNA 23(11):1685-1699 PMID: 28808125
- 5. Mizutani T et al.. 1998. The dual identities of mammalian tRNA(Sec) for SerRS and selenocysteine synthase.. Mol Biol Rep 25(4):211-6 PMID: 9870610
- 6. French RL et al.. 2014. Structural asymmetry of the terminal catalytic complex in selenocysteine synthesis.. J Biol Chem 289(42):28783-94 PMID: 25190812
- 7. Sturchler-Pierrat C et al.. 1995. Selenocysteylation in eukaryotes necessitates the uniquely long aminoacyl acceptor stem of selenocysteine tRNA(Sec).. J Biol Chem 270(31):18570-4 PMID: 7629188
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