GO:0035600 tRNA methylthiolation: RNA Modification Pathway, Genes, Functions and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0035600 tRNA methylthiolation is the biological process that adds a methylthioether group (-SCH3) to a nucleotide in a tRNA molecule, as defined by QuickGO.
• The reaction is catalyzed by the radical SAM enzyme MiaB, which uses iron-sulfur clusters and S-adenosylmethionine to install the methylthio group at position 2 of N6-isopentenyladenosine (i6A) in tRNA.
• Methylthiolation is conserved from bacteria to humans and is essential for accurate codon recognition, translational fidelity, and efficient protein synthesis.
• Reactive sulfur species and iron-sulfur cluster integrity regulate MiaB activity, linking tRNA modification to sulfur metabolism and insulin secretion.
• Defective tRNA methylthiolation has been implicated in age-related hearing loss, mitochondrial dysfunction, and metabolic disease, making it a target for therapeutic intervention.
• CRISPR knockout, point-mutation, and knock-in models of MiaB and related genes enable causal dissection of tRNA methylthiolation in human disease and cell biology.
Description
tRNA methylthiolation (GO:0035600) is a conserved post-transcriptional RNA modification in which a methylthioether group (-SCH3) is added to a nucleotide within a transfer RNA molecule. This modification is critical for the structure and function of tRNA, particularly at the anticodon loop, where it influences codon-anticodon pairing and translational accuracy. The enzyme responsible for this modification in bacteria and eukaryotes is MiaB, a member of the radical S-adenosylmethionine (SAM) superfamily that utilizes iron-sulfur clusters to catalyze the methylthiolation of N6-isopentenyladenosine (i6A) at position 37 of certain tRNAs. The reaction is essential for normal cellular physiology, and its disruption leads to translational defects and disease phenotypes.
tRNA methylthiolation At A Glance
| GO ID | GO:0035600 |
|---|---|
| GO term | tRNA methylthiolation |
| Ontology | biological_process |
| Synonym | None |
| Major function | Addition of a methylthioether group (-SCH3) to a nucleotide in tRNA, typically at position 37, to enhance translational fidelity and efficiency |
| Catalytic enzyme | MiaB (radical SAM enzyme) in bacteria and eukaryotes |
| Substrate | N6-isopentenyladenosine (i6A) in tRNA |
| Product | 2-methylthio-N6-isopentenyladenosine (ms2i6A) |
| Cofactors | Iron-sulfur cluster, S-adenosylmethionine (SAM) |
| Conservation | Conserved from bacteria to humans |
What Is GO:0035600?
According to the Gene Ontology, GO:0035600 (tRNA methylthiolation) is defined as the addition of a methylthioether group (-SCH3) to a nucleotide in a tRNA molecule. This process is a biological process that modifies tRNA post-transcriptionally, enhancing its function in protein synthesis. The modification typically occurs at the 2-position of N6-isopentenyladenosine (i6A) to form 2-methylthio-N6-isopentenyladenosine (ms2i6A), a modification that stabilizes codon-anticodon interactions and ensures translational fidelity.
Why Is tRNA methylthiolation Important in Cell Biology?
tRNA methylthiolation is essential for accurate and efficient protein synthesis, as the ms2i6A modification stabilizes codon-anticodon interactions and prevents frameshifting. Defects in this process impair mitochondrial translation, reduce insulin secretion, and contribute to age-related hearing loss, highlighting its broad physiological significance. Moreover, the iron-sulfur cluster-dependent mechanism of MiaB links tRNA modification to cellular sulfur and iron homeostasis, making it a nexus for metabolic and neurodegenerative research.
• Ensures translational fidelity by stabilizing codon-anticodon pairing at the ribosome.
• Required for efficient mitochondrial protein synthesis and oxidative phosphorylation.
• Regulates insulin secretion in pancreatic beta cells via reactive sulfur species.
• Implicated in age-related hearing loss and mitochondrial dysfunction.
• Links tRNA modification to iron-sulfur cluster metabolism and radical SAM enzymology.
• Provides a model for studying radical SAM enzyme mechanisms and C-S bond formation.
• Potential therapeutic target for metabolic disorders and hearing loss.
• Essential for bacterial operon regulation and stress responses.
• Serves as a paradigm for RNA modification crosstalk and epitranscriptomics.
• Enables CRISPR-based functional genomics of tRNA modification pathways.
What Happens During tRNA methylthiolation?
Substrate Recognition and i6A Formation
In simple terms: First, the tRNA is tagged with a prenyl group to create the substrate for methylthiolation.
tRNA methylthiolation requires prior isopentenylation of adenosine at position 37 to form N6-isopentenyladenosine (i6A). This step is catalyzed by tRNA isopentenyltransferase (MiaA in bacteria, TRIT1 in humans). The i6A modification is a prerequisite for MiaB-mediated methylthiolation, as MiaB specifically recognizes i6A-containing tRNA substrates.
Radical SAM Activation and Sulfur Insertion
In simple terms: The enzyme MiaB uses an iron-sulfur cluster and SAM to generate a reactive radical that inserts sulfur into the tRNA.
MiaB is a radical S-adenosylmethionine (SAM) enzyme that contains two [4Fe-4S] clusters. One cluster binds SAM and reductively cleaves it to generate a 5'-deoxyadenosyl radical, which abstracts a hydrogen atom from the methyl group of i6A. The second cluster is proposed to bind and deliver the sulfur atom from a sulfur donor (likely a persulfide or thiocarboxylate) to form the methylthioether group. Structural studies reveal a unique domain architecture that positions the substrate and sulfur donor for catalysis.
Methyl Group Transfer and ms2i6A Formation
In simple terms: A methyl group is transferred to the sulfur, completing the methylthioether modification on the tRNA.
Following sulfur insertion, a methyl group from SAM is transferred to the sulfur atom, yielding the final product 2-methylthio-N6-isopentenyladenosine (ms2i6A). This step may involve a methyltransferase activity intrinsic to MiaB or a separate enzyme. The reaction is tightly coupled to the radical SAM mechanism and requires reductive conditions and iron-sulfur cluster integrity.
Regulation by Reactive Sulfur Species and Iron-Sulfur Clusters
In simple terms: The availability of sulfur and iron-sulfur clusters controls how much methylthiolation occurs.
Reactive sulfur species (RSS) such as cysteine persulfide regulate MiaB activity by providing sulfur for the reaction. In pancreatic beta cells, RSS levels modulate tRNA methylthiolation and insulin secretion, linking this modification to metabolic signaling. Iron-sulfur cluster assembly and repair pathways also influence MiaB function, as mutations or oxidative stress that damage clusters impair methylthiolation.
Physiological Consequences of Methylthiolation
In simple terms: The modified tRNA works better in translation, affecting protein production and cellular health.
The ms2i6A modification enhances the efficiency and fidelity of translation by stabilizing codon-anticodon interactions, particularly for codons ending in U. In mitochondria, loss of methylthiolation leads to impaired oxidative phosphorylation and age-related hearing loss. In bacteria, methylthiolation affects operon expression and stress responses. Thus, tRNA methylthiolation is a critical determinant of proteostasis and cellular function.
Key Genes Involved in GO:0035600 tRNA methylthiolation
The following genes and proteins are central to tRNA methylthiolation, as supported by published literature.
| Gene | Major Role | Research Relevance |
|---|---|---|
| MiaB | Radical SAM enzyme that catalyzes methylthiolation of i6A in tRNA | Core enzyme; structural and mechanistic studies |
| MiaA | Isopentenyltransferase that forms i6A, the substrate for MiaB | Upstream modification; knockout affects methylthiolation |
| TRIT1 | Human homolog of MiaA; isopentenylates tRNA | Human disease links; mitochondrial tRNA modification |
| CDK5RAP1 | Human homolog of MiaB; mitochondrial tRNA methylthiolation | Mitochondrial function and hearing loss |
| IscS | Cysteine desulfurase involved in iron-sulfur cluster assembly | Provides sulfur for MiaB; cluster biogenesis |
| IscU | Scaffold protein for iron-sulfur cluster assembly | Cluster assembly for MiaB |
| SufA | Iron-sulfur cluster assembly protein | Alternative cluster pathway |
| Nfs1 | Cysteine desulfurase in eukaryotes | Mitochondrial iron-sulfur cluster biogenesis |
| ISD11 | Accessory protein for Nfs1 | Eukaryotic cluster assembly |
| Frataxin | Iron chaperone for cluster assembly | Friedreich ataxia; affects MiaB |
| CyaY | Iron-binding protein in cluster assembly | Regulates cluster formation |
| SAM | Cofactor for radical generation and methyl transfer | Essential for MiaB activity |
| tRNA (i6A-containing) | Substrate for methylthiolation | Substrate specificity and modification mapping |
| Reactive sulfur species | Regulate MiaB activity and sulfur supply | Metabolic regulation; insulin secretion |
| MiaB homologs | Conserved enzymes in bacteria and eukaryotes | Evolutionary and functional studies |
| Mitochonic acid 5 | Pharmacological agent targeting defective methylthiolation | Therapeutic for hearing loss |
How Is tRNA methylthiolation Regulated?
tRNA methylthiolation is regulated at multiple levels. The availability of reactive sulfur species (RSS) directly modulates MiaB activity, as RSS provide the sulfur for the methylthioether group and influence insulin secretion in pancreatic beta cells. Iron-sulfur cluster assembly and repair pathways control the maturation and activity of MiaB, with defects in cluster biogenesis leading to reduced methylthiolation. Additionally, the expression of MiaB and its homologs may be subject to transcriptional and post-transcriptional regulation in response to cellular stress, although specific mechanisms require further study.
tRNA methylthiolation and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| CDK5RAP1 | Age-related hearing loss | Knockout mouse; mitochonic acid 5 treatment |
| MiaB | Metabolic disorders | Beta-cell-specific knockout; insulin secretion assays |
| TRIT1 | Mitochondrial dysfunction | Patient-derived fibroblasts; CRISPR correction |
| IscS | Iron-sulfur cluster diseases | Knockout cell lines; cluster assembly assays |
| MiaA | Translational fidelity defects | Bacterial knockout; ribosome profiling |
Age-Related Hearing Loss and Mitochondrial Dysfunction
Defective tRNA methylthiolation in mitochondria contributes to age-related hearing loss. Mutations in CDK5RAP1, the human homolog of MiaB, impair mitochondrial translation and lead to progressive hearing loss in animal models. Mitochonic acid 5, a compound that targets defective 2-methylthiolation, mitigates hearing loss progression, suggesting a therapeutic avenue.
Metabolic Disorders and Insulin Secretion
Reactive sulfur species regulate tRNA methylthiolation and contribute to insulin secretion in pancreatic beta cells. Dysregulation of this pathway may impair glucose-stimulated insulin secretion, linking tRNA modification to type 2 diabetes and metabolic syndrome.
Neurodegeneration and Translational Stress
Impaired tRNA methylthiolation can cause translational stress and activate the integrated stress response, which is implicated in neurodegenerative diseases such as Alzheimer's and Parkinson's. However, direct evidence for MiaB mutations in neurodegeneration is still emerging.
From tRNA methylthiolation-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| Does MiaB loss impair translation? | MiaB knockout cell line; Ribo-seq |
| How does a point mutation in MiaB affect catalysis? | Point-mutation knock-in via CRISPR |
| Can wild-type MiaB rescue methylthiolation? | Knock-in of tagged MiaB; overexpression |
| What is the role of RSS in insulin secretion? | Beta-cell knockout of MiaB; RSS supplementation |
| Does CDK5RAP1 mutation cause hearing loss? | Knockout mouse; auditory brainstem response |
| How do iron-sulfur clusters regulate MiaB? | Knockout of IscS; cluster analysis |
How to Study the tRNA methylthiolation Process
| Method | What It Measures | Typical Application |
|---|---|---|
| Ribo-seq | Translation efficiency and ribosome pausing | Assess impact of methylthiolation on protein synthesis |
| LC-MS/MS | tRNA modification levels | Quantify ms2i6A in knockout/knock-in cells |
| EPR spectroscopy | Iron-sulfur cluster state | Characterize MiaB mutants |
| CRISPR knockout screens | Gene essentiality and modifier identification | Discover pathways regulating methylthiolation |
| Northern blot | tRNA levels and integrity | Confirm tRNA stability in mutants |
| Polysome profiling | Ribosome association | Measure global translation changes |
| Immunoblotting | Protein expression | Validate MiaB knockout or overexpression |
| Seahorse assay | Mitochondrial respiration | Assess mitochondrial function in CDK5RAP1 mutants |
Ribosome Profiling (Ribo-seq)
Ribo-seq measures translation efficiency and codon occupancy at single-codon resolution. In tRNA methylthiolation studies, Ribo-seq can reveal increased ribosome pausing at codons that depend on ms2i6A-modified tRNA, providing functional evidence for the modification's role in translation.
RNA Mass Spectrometry and Modification Mapping
Liquid chromatography-tandem mass spectrometry (LC-MS/MS) enables direct detection and quantification of ms2i6A in tRNA. This method is used to confirm the loss or restoration of methylthiolation in knockout or knock-in models.
Iron-Sulfur Cluster Analysis
UV-visible absorption spectroscopy, electron paramagnetic resonance (EPR), and iron/sulfide quantification assays are used to characterize the iron-sulfur clusters in MiaB and assess the impact of mutations or oxidative stress.
CRISPR Screening and Functional Genomics
Genome-wide CRISPR knockout screens can identify genes that modulate tRNA methylthiolation or its downstream effects. Coupled with sequencing and bioinformatics, these screens reveal pathways that interact with MiaB and ms2i6A.
How CRISPR Can Be Used to Study GO:0035600 tRNA methylthiolation
Knockout
CRISPR knockout of MiaB or CDK5RAP1 in human cell lines abolishes tRNA methylthiolation, leading to translational defects and mitochondrial dysfunction. These models are used to study the physiological consequences of losing ms2i6A and to test rescue by wild-type or mutant enzymes.
Point Mutation
CRISPR-mediated point mutations in the catalytic residues of MiaB or in the iron-sulfur cluster ligands can dissect the mechanism of methylthiolation. Such models help distinguish between defects in substrate binding, radical generation, and sulfur insertion.
Knock-in
Knock-in of tagged MiaB (e.g., FLAG or HA) allows affinity purification and proteomic analysis of the methylthiolation complex. Knock-in of disease-associated variants can model human pathologies such as hearing loss or metabolic disorders.
Overexpression
Overexpression of MiaB or its homologs in mammalian cells can enhance methylthiolation and rescue phenotypes caused by endogenous mutations. This approach is useful for structure-function studies and for producing large quantities of modified tRNA for biochemical assays.
How EDITGENE Supports tRNA methylthiolation Research
Researchers studying tRNA methylthiolation-related genes often need to determine whether a candidate gene is causally involved in the modification, how mutations affect enzyme function, and what downstream pathways are perturbed. EDITGENE provides end-to-end CRISPR solutions to generate precisely engineered cell models for such investigations.
Contact EDITGENE today to design your custom CRISPR model for tRNA methylthiolation research.
Frequently Asked Questions About tRNA methylthiolation
What is tRNA methylthiolation?
tRNA methylthiolation (GO:0035600) is the addition of a methylthioether group (-SCH3) to a nucleotide in a tRNA molecule, typically at position 37, catalyzed by the radical SAM enzyme MiaB.
What genes are involved in tRNA methylthiolation?
Key genes include MiaB (catalytic enzyme), MiaA/TRIT1 (isopentenyltransferase), CDK5RAP1 (human MiaB homolog), and iron-sulfur cluster assembly genes such as IscS and Nfs1.
What is the function of MiaB in tRNA methylthiolation?
MiaB is a radical SAM enzyme that uses iron-sulfur clusters and SAM to catalyze the methylthiolation of i6A in tRNA, forming ms2i6A.
How is tRNA methylthiolation regulated?
It is regulated by reactive sulfur species, iron-sulfur cluster availability, and cellular stress pathways that affect MiaB activity.
What diseases are associated with defective tRNA methylthiolation?
Defective methylthiolation is linked to age-related hearing loss, mitochondrial dysfunction, and metabolic disorders such as impaired insulin secretion.
What methods are used to study tRNA methylthiolation?
Common methods include LC-MS/MS for modification detection, Ribo-seq for translation analysis, EPR for iron-sulfur cluster characterization, and CRISPR screens for gene discovery.
Can CRISPR be used to study tRNA methylthiolation?
Yes, CRISPR knockout, point mutation, knock-in, and overexpression models enable precise functional studies of MiaB and related genes.
What is the role of iron-sulfur clusters in tRNA methylthiolation?
Iron-sulfur clusters in MiaB are essential for radical generation and sulfur insertion during the methylthiolation reaction.
Is tRNA methylthiolation conserved in humans?
Yes, the process is conserved from bacteria to humans, with CDK5RAP1 as the human homolog of MiaB.
How does tRNA methylthiolation affect insulin secretion?
Reactive sulfur species regulate tRNA methylthiolation, and this modification contributes to insulin secretion in pancreatic beta cells.
Conclusion
tRNA methylthiolation (GO:0035600) is a conserved and essential RNA modification that ensures translational fidelity and cellular homeostasis. The radical SAM enzyme MiaB, along with iron-sulfur cluster and sulfur metabolism pathways, orchestrates this modification, and its dysfunction is linked to hearing loss, metabolic disorders, and mitochondrial disease. CRISPR-based models are powerful tools to dissect the molecular mechanisms and therapeutic potential of tRNA methylthiolation.
References
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- 2. Takahashi N et al.. 2017. Reactive sulfur species regulate tRNA methylthiolation and contribute to insulin secretion.. Nucleic Acids Res 45(1):435-445 PMID: 27568003
- 3. Ma ZH et al.. 2025. Iron-Sulfur-Mediated C-S Bond Formation: Mechanistic Insights from the state-crossing tRNA Methylthiolation by the Radical SAM Enzyme MiaB.. Chemistry 31(49):e01463 PMID: 40778570
- 4. Kimura S et al.. 2015. Iron-sulfur proteins responsible for RNA modifications.. Biochim Biophys Acta 1853(6):1272-83 PMID: 25533083
- 5. Kouga T et al.. 2025. Mitochonic acid 5 mitigates age-related hearing loss progression by targeting defective 2-methylthiolation in mitochondrial transfer RNAs.. Front Cell Neurosci 19:1541347 PMID: 40260078
- 6. Frey PA et al.. 2008. The Radical SAM Superfamily.. Crit Rev Biochem Mol Biol 43(1):63-88 PMID: 18307109
- 7. Wei FY et al.. 2016. [Molecular basis of tRNA methylthiolation and the pathological implications].. Seikagaku 88(3):328-34 PMID: 27483951
- 8. Buck M et al.. 1982. Iron mediated methylthiolation of tRNA as a regulator of operon expression in Escherichia coli.. Nucleic Acids Res 10(8):2609-24 PMID: 7043398
