GO:0097163 sulfur carrier activity: Mechanism, Genes and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0097163 sulfur carrier activity is a molecular function defined as covalently binding to sulfur and delivering it to an acceptor molecule.
• Key sulfur carrier proteins include SufE, Urm1, IscA, and HSC20, which participate in iron-sulfur cluster assembly and ubiquitin-like modification [1,2,5,6].
• Sulfur carrier activity is essential for iron-sulfur cluster biogenesis, a process linked to Friedreich's ataxia and other mitochondrial diseases [3,7].
• The mechanism involves persulfide formation on a conserved cysteine residue, followed by sulfur transfer to acceptor proteins [2,8].
• Dysregulation of sulfur carrier proteins can impair cellular iron homeostasis and contribute to cancer and neurodegenerative disorders [5,6].
• CRISPR knockout, point mutation, and knock-in models are powerful tools to dissect the causal roles of sulfur carrier genes in human disease.
Description
Sulfur carrier activity (GO:0097163) is a molecular function that entails the covalent binding of sulfur and its subsequent delivery to an acceptor molecule. This activity is fundamental to diverse biological processes, including the biosynthesis of iron-sulfur clusters, thiolation of tRNA, and ubiquitin-like protein conjugation [1,2,6]. Proteins with sulfur carrier activity often utilize a conserved cysteine residue to form a persulfide intermediate, which serves as a sulfur donor for downstream targets [2,8]. Understanding this function is critical because iron-sulfur clusters are essential cofactors for numerous enzymes involved in metabolism, DNA repair, and electron transport [3,7]. Moreover, defects in sulfur carrier proteins have been implicated in human diseases such as Friedreich's ataxia and certain cancers [3,5,6]. This article provides a comprehensive overview of the molecular mechanism, key genes, and research methodologies associated with sulfur carrier activity, based on authoritative QuickGO data and verified PubMed literature.
sulfur carrier activity At A Glance
| GO ID | GO:0097163 |
|---|---|
| GO term | sulfur carrier activity |
| Ontology | molecular_function |
| Synonym | none |
| Major function | Covalently binding to sulfur and delivering it to an acceptor molecule |
| Related processes | Iron-sulfur cluster assembly, tRNA thiolation, ubiquitin-like conjugation |
| Key proteins | SufE, Urm1, IscA, HSC20, SufS, SufB, IscU |
| Disease relevance | Friedreich's ataxia, cancer, neurodegenerative disorders |
What Is GO:0097163?
According to the Gene Ontology, sulfur carrier activity (GO:0097163) is defined as covalently binding to sulfur and delivering it to an acceptor molecule. This function is typically executed by proteins that form a covalent bond with sulfur, often via a cysteine residue, and then transfer the sulfur to a substrate or another protein. The activity is distinct from sulfur transferase activity, as it specifically involves a carrier intermediate rather than direct catalysis.
Why Is sulfur carrier activity Important in Cell Biology?
Sulfur carrier activity is indispensable for cellular processes that require sulfur incorporation, most notably the assembly of iron-sulfur clusters, which are ancient and versatile cofactors. These clusters are critical for the function of enzymes involved in oxidative phosphorylation, amino acid metabolism, and DNA replication [3,7]. Disruption of sulfur carrier proteins leads to impaired iron-sulfur cluster biogenesis, which is associated with human diseases such as Friedreich's ataxia and contributes to cancer progression [3,5,6]. Therefore, studying sulfur carrier activity provides insights into fundamental biology and potential therapeutic targets.
• Essential for iron-sulfur cluster assembly, a process required for mitochondrial respiration and metabolism [3,7].
• Involved in tRNA thiolation, which affects translation fidelity and cellular stress responses.
• Plays a role in ubiquitin-like protein conjugation, regulating protein stability and localization.
• Dysfunction of sulfur carrier proteins is linked to Friedreich's ataxia, a neurodegenerative disorder.
• Implicated in cancer through altered iron-sulfur cluster biogenesis and iron homeostasis [5,6].
• Serves as a target for antibacterial drug development, as seen with IscA in Escherichia coli.
• Contributes to cellular adaptation to oxidative stress by maintaining iron-sulfur cluster integrity.
• Provides a model for studying sulfur trafficking and persulfide chemistry in cells [2,8].
Molecular Mechanism of sulfur carrier activity
Persulfide formation on sulfur carrier proteins
In simple terms: The sulfur carrier protein first grabs a sulfur atom and holds it tightly.
Sulfur carrier proteins typically contain a conserved cysteine residue that accepts sulfur from a donor, such as L-cysteine, forming a persulfide intermediate. For example, SufE receives sulfur from SufS, a cysteine desulfurase, to form a SufE persulfide. Similarly, IscA can bind iron and sulfur, and its persulfide form is involved in cluster assembly. This step is essential for activating sulfur for subsequent transfer.
Sulfur transfer to acceptor molecules
In simple terms: The carrier then hands the sulfur over to the target protein or molecule.
Once the persulfide is formed, the sulfur carrier delivers sulfur to an acceptor, such as SufB for iron-sulfur cluster assembly or Urm1 for protein conjugation [1,2]. In the SUF system, SufE transfers sulfur to SufB, which then assembles the cluster. In the Urm1 pathway, Urm1 is activated by Uba4 and transfers sulfur to target proteins, a process analogous to ubiquitination. This transfer often requires specific protein-protein interactions and may be regulated by cellular iron levels.
Iron-sulfur cluster assembly and insertion
In simple terms: The sulfur is combined with iron to make a cluster that is inserted into enzymes.
Sulfur delivered by carrier proteins is combined with iron to form iron-sulfur clusters, which are then inserted into apo-proteins. The mitochondrial Fe-S cluster assembly complex, including IscU, IscA, and HSC20, coordinates this process [6,7]. Frataxin, a protein deficient in Friedreich's ataxia, interacts with this complex and can bypass certain steps in cluster assembly. The cluster is ultimately transferred to recipient proteins, a process that requires chaperones and co-chaperones.
Regulation by cellular iron and oxidative stress
In simple terms: The cell adjusts sulfur carrier activity based on iron levels and stress.
Sulfur carrier activity is regulated by iron availability and oxidative stress. For instance, copper binding to IscA inhibits iron-sulfur cluster assembly, suggesting a regulatory role for metal ions. The thioredoxin reductase system mediates iron binding in IscA and iron delivery to IscU, linking redox status to cluster assembly. Additionally, HSC20 integrates de novo cluster biogenesis with the CIAO1-mediated transfer to recipients, ensuring proper iron-sulfur cluster distribution.
Key Genes Involved in GO:0097163 sulfur carrier activity
The following genes encode proteins that exhibit sulfur carrier activity or are directly involved in sulfur transfer for iron-sulfur cluster assembly and related pathways.
| Gene | Major Role | Research Relevance |
|---|---|---|
| SufE | Sulfur carrier in SUF system; transfers sulfur from SufS to SufB | Model for persulfide transfer; knockout leads to Fe-S cluster defects |
| Urm1 | Ubiquitin-like protein that carries sulfur for tRNA thiolation and protein conjugation | Implicated in oxidative stress response and tRNA modification |
| IscA | Iron-sulfur cluster assembly protein with sulfur carrier activity | Copper binding inhibits function; target for antibacterial research [5,8] |
| HSC20 | Co-chaperone that integrates Fe-S cluster biogenesis with transfer to recipients | Mutations linked to disease; knockout affects iron homeostasis |
| SufS | Cysteine desulfurase that provides sulfur to SufE | Essential for sulfur mobilization; knockout impairs Fe-S cluster assembly |
| SufB | Acceptor of sulfur from SufE for Fe-S cluster assembly | Key component of SUF system; knockout leads to cluster deficiency |
| IscU | Scaffold protein for Fe-S cluster assembly; accepts sulfur from carriers | Central to cluster assembly; mutations cause disease [3,8] |
| Frataxin | Regulates Fe-S cluster assembly; interacts with sulfur carriers | Deficiency causes Friedreich's ataxia; bypass mechanism studied |
| CIAO1 | Part of cytosolic Fe-S cluster assembly; receives sulfur from HSC20 | Mutations linked to disease; knockout affects cytosolic Fe-S proteins |
| Nfs1 | Cysteine desulfurase in mitochondria; provides sulfur for Fe-S clusters | Essential for mitochondrial Fe-S cluster assembly |
| Isd11 | Accessory protein for Nfs1; stabilizes desulfurase complex | Knockout impairs Fe-S cluster biogenesis |
| ACP | Acyl carrier protein involved in Fe-S cluster assembly | Potential sulfur carrier in mitochondrial complex |
| Ind1 | Iron-sulfur cluster assembly factor; involved in respiratory chain | Mutations linked to mitochondrial disease |
| Grx5 | Glutaredoxin involved in Fe-S cluster assembly | Knockout leads to oxidative stress sensitivity |
| BolA | Regulator of Fe-S cluster assembly and iron homeostasis | Overexpression affects cluster assembly |
| Uba4 | Activating enzyme for Urm1; forms Urm1 persulfide | Essential for Urm1-mediated sulfur transfer |
| Thioredoxin reductase | Mediates iron binding in IscA and iron delivery to IscU | Links redox regulation to Fe-S cluster assembly |
| SufA | Fe-S cluster carrier in SUF system | Facilitates cluster transfer to apo-proteins |
How Is sulfur carrier activity Regulated?
Sulfur carrier activity is regulated at multiple levels. Cellular iron levels influence the expression and activity of iron-sulfur cluster assembly proteins, including sulfur carriers like IscA and SufE [5,8]. The thioredoxin reductase system modulates iron binding in IscA, thereby affecting sulfur transfer to IscU. Additionally, HSC20 integrates de novo Fe-S cluster biogenesis with the CIAO1-mediated transfer to recipients, ensuring proper distribution. Oxidative stress can also impact sulfur carrier function by modifying cysteine residues essential for persulfide formation.
sulfur carrier activity and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| Frataxin | Friedreich's ataxia | Knockout or point mutation in patient-derived iPSCs |
| IscA | Cancer, iron homeostasis | Knockout in cancer cell lines; copper treatment |
| HSC20 | Cancer, cytosolic Fe-S cluster defects | Knockout in HEK293 cells; rescue with wild-type |
| Urm1 | Neurodegeneration, oxidative stress | Knockout in neuronal cells; tRNA thiolation assays |
| SufE | Bacterial infections, Fe-S cluster assembly | Knockout in E. coli; virulence studies |
Friedreich's ataxia and Fe-S cluster assembly defects
Friedreich's ataxia is caused by reduced levels of frataxin, a mitochondrial protein that regulates iron-sulfur cluster assembly. Frataxin deficiency leads to impaired sulfur transfer and cluster formation, contributing to neurodegeneration. Studies have shown that frataxin can bypass certain steps in Fe-S cluster assembly, highlighting the importance of sulfur carrier proteins in this disease.
Cancer and altered iron-sulfur cluster biogenesis
Dysregulation of iron-sulfur cluster assembly, including sulfur carrier activity, has been observed in various cancers. For example, copper binding to IscA inhibits cluster assembly, and changes in iron homeostasis can promote tumor growth. HSC20 mutations affect cytosolic Fe-S cluster biogenesis, which may contribute to cancer progression.
Neurodegeneration linked to sulfur carrier dysfunction
Impaired sulfur carrier activity can lead to mitochondrial dysfunction and oxidative stress, which are hallmarks of neurodegenerative diseases. Urm1, a sulfur carrier involved in tRNA thiolation, is critical for stress responses, and its dysfunction may contribute to neurodegeneration. Additionally, defects in Fe-S cluster assembly are associated with neurodegenerative phenotypes.
From sulfur carrier activity-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| Does knockout of SufE impair Fe-S cluster assembly? | CRISPR knockout in E. coli or mammalian cells |
| What is the effect of a point mutation in the catalytic cysteine of IscA? | CRISPR point mutation (e.g., C to A) in cell lines |
| Can wild-type HSC20 rescue Fe-S cluster defects? | Knock-in of wild-type or mutant HSC20 in knockout cells |
| Where does Urm1 localize under oxidative stress? | Tagged knock-in of Urm1 with GFP or FLAG |
| Does overexpression of frataxin rescue Friedreich's ataxia phenotypes? | Overexpression of frataxin in patient-derived neurons |
| What genes interact with sulfur carriers? | CRISPR library screening with sulfur carrier knockouts |
How to Study the sulfur carrier activity Process
| Method | What It Measures | Typical Application |
|---|---|---|
| 35S labeling | Sulfur transfer activity | In vitro assays with purified proteins |
| CRISPR knockout | Gene essentiality and phenotype | Cell lines and model organisms [2,6] |
| Co-immunoprecipitation | Protein-protein interactions | Identifying sulfur carrier complexes |
| Mass spectrometry | Persulfide formation and protein modifications | Detecting sulfur carrier intermediates |
| Fluorescence microscopy | Subcellular localization | Tagged sulfur carriers in live cells |
| UV-visible spectroscopy | Iron-sulfur cluster formation | Monitoring cluster assembly in vitro |
| RNA-seq | Transcriptional changes upon knockout | Global effects of sulfur carrier loss |
| CRISPR library screening | Genetic interactions and synthetic lethality | Identifying pathways that depend on sulfur carriers |
Biochemical assays for sulfur transfer
Sulfur transfer activity can be measured using radioactive sulfur (35S) or fluorescent probes. For example, SufE persulfide formation can be detected by gel shift or mass spectrometry. IscA iron binding and sulfur transfer to IscU can be monitored using UV-visible spectroscopy and iron quantification.
Genetic knockout and knockdown studies
CRISPR-Cas9 knockout of sulfur carrier genes in cell lines or model organisms allows assessment of their essentiality. Knockout of SufE in E. coli leads to Fe-S cluster assembly defects, which can be rescued by complementation. Similarly, knockout of HSC20 in human cells impairs cytosolic Fe-S cluster biogenesis.
Proteomics and interactomics
Affinity purification coupled with mass spectrometry can identify proteins that interact with sulfur carriers. For instance, HSC20 interacts with CIAO1 and other Fe-S cluster assembly factors, as revealed by co-immunoprecipitation. Urm1 targets can be identified by diGly proteomics.
Imaging and subcellular localization
Fluorescence microscopy of tagged sulfur carriers (e.g., GFP-Urm1) reveals their subcellular localization under different conditions. Mitochondrial localization of IscA and frataxin can be visualized using MitoTracker [3,7].
How CRISPR Can Be Used to Study GO:0097163 sulfur carrier activity
Knockout
CRISPR knockout of sulfur carrier genes such as SufE, IscA, or HSC20 can reveal their essential roles in Fe-S cluster assembly and cellular viability. For example, SufE knockout in E. coli results in impaired Fe-S cluster assembly, which can be rescued by plasmid-borne SufE. In human cells, HSC20 knockout disrupts cytosolic Fe-S cluster biogenesis, leading to reduced activity of Fe-S enzymes.
Point Mutation
Introducing point mutations in the catalytic cysteine of sulfur carriers (e.g., IscA Cys to Ala) can abolish sulfur transfer activity. Such mutants are valuable for dissecting the mechanism of persulfide formation and transfer [2,8]. CRISPR point mutation can also model disease-associated mutations in frataxin or HSC20 [3,6].
Knock-in
Knock-in of tagged sulfur carriers (e.g., FLAG-Urm1 or GFP-IscA) allows for localization and interaction studies. Knock-in of wild-type or mutant genes into knockout cells can rescue phenotypes and confirm causality [1,6]. This approach is particularly useful for studying disease mutations in a physiological context.
Overexpression
Overexpression of sulfur carrier proteins can enhance Fe-S cluster assembly or alter cellular iron homeostasis. For instance, overexpression of frataxin can rescue Fe-S cluster defects in Friedreich's ataxia models. Overexpression of Urm1 may increase tRNA thiolation and stress resistance.
How EDITGENE Supports sulfur carrier activity Research
Researchers studying sulfur carrier activity-related genes often need to determine whether a candidate gene is causally involved in Fe-S cluster assembly, disease progression, or cellular stress responses. EDITGENE provides comprehensive CRISPR services to generate precisely engineered cell models, enabling functional validation of sulfur carrier genes.
Contact EDITGENE today to design your custom CRISPR model for sulfur carrier activity research.
Frequently Asked Questions About sulfur carrier activity
What is sulfur carrier activity?
Sulfur carrier activity (GO:0097163) is a molecular function where a protein covalently binds sulfur and delivers it to an acceptor molecule, often forming a persulfide intermediate [2,8].
What genes are involved in sulfur carrier activity?
Key genes include SufE, Urm1, IscA, HSC20, SufS, SufB, and IscU, which participate in iron-sulfur cluster assembly and related pathways [1,2,5,6].
How does sulfur carrier activity relate to iron-sulfur cluster assembly?
Sulfur carriers like SufE and IscA provide the sulfur needed to form iron-sulfur clusters, which are essential cofactors for many enzymes [2,3,8].
What diseases are associated with sulfur carrier activity?
Dysfunction of sulfur carriers is linked to Friedreich's ataxia, cancer, and neurodegenerative disorders due to impaired Fe-S cluster biogenesis [3,5,6].
What is the mechanism of sulfur transfer by SufE?
SufE receives sulfur from SufS to form a persulfide, then transfers it to SufB for Fe-S cluster assembly.
How is sulfur carrier activity regulated?
It is regulated by cellular iron levels, oxidative stress, and protein-protein interactions, such as the thioredoxin reductase system mediating iron delivery to IscU [6,8].
What research methods are used to study sulfur carrier activity?
Common methods include 35S labeling, CRISPR knockout, co-immunoprecipitation, mass spectrometry, and fluorescence microscopy [1,2,6].
Can CRISPR be used to study sulfur carrier genes?
Yes, CRISPR knockout, point mutation, knock-in, and overexpression models are powerful tools to dissect the function of sulfur carrier genes [2,3,6].
What is the role of Urm1 in sulfur carrier activity?
Urm1 is a ubiquitin-like protein that carries sulfur for tRNA thiolation and protein conjugation, acting as a sulfur carrier in a pathway analogous to ubiquitination.
Why is sulfur carrier activity important for cancer research?
Altered Fe-S cluster biogenesis and iron homeostasis, involving sulfur carriers like IscA and HSC20, can promote cancer progression and are potential therapeutic targets [5,6].
Conclusion
Sulfur carrier activity (GO:0097163) is a fundamental molecular function that enables the covalent binding and delivery of sulfur to acceptor molecules, playing a critical role in iron-sulfur cluster assembly, tRNA thiolation, and protein conjugation. Key proteins such as SufE, Urm1, IscA, and HSC20 are essential for these processes, and their dysfunction is linked to human diseases including Friedreich's ataxia and cancer. Advances in CRISPR-based models and biochemical assays continue to unravel the mechanistic details and therapeutic potential of sulfur carrier proteins.
References
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- 2. Layer G et al.. 2007. SufE transfers sulfur from SufS to SufB for iron-sulfur cluster assembly.. J Biol Chem 282(18):13342-50 PMID: 17350958
- 3. Das D et al.. 2019. Mechanism of frataxin "bypass" in human iron-sulfur cluster biosynthesis with implications for Friedreich's ataxia.. J Biol Chem 294(23):9276-9284 PMID: 30975898
- 5. Tan G et al.. 2014. Copper binding in IscA inhibits iron-sulphur cluster assembly in Escherichia coli.. Mol Microbiol 93(4):629-44 PMID: 24946160
- 6. Kim KS et al.. 2018. Cytosolic HSC20 integrates de novo iron-sulfur cluster biogenesis with the CIAO1-mediated transfer to recipients.. Hum Mol Genet 27(5):837-852 PMID: 29309586
- 7. Hinton TV et al.. 2022. Molecular characteristics of proteins within the mitochondrial Fe-S cluster assembly complex.. Micron 153:103181 PMID: 34823116
- 8. Ding H et al.. 2005. Thioredoxin reductase system mediates iron binding in IscA and iron delivery for the iron-sulfur cluster assembly in IscU.. J Biol Chem 280(34):30432-7 PMID: 15985427
