GO:0099128 mitochondrial [2Fe-2S] assembly complex: Components, Assembly and Research Methods, Genes, Functions and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0099128 defines the mitochondrial [2Fe-2S] assembly complex, a protein machine that builds iron-sulfur clusters inside mitochondria.
• In humans, the complex contains ISCU, NFS1, LYRM4, NDUFAB1 and FXN, which cooperate to assemble 2Fe-2S clusters.
• These clusters are essential cofactors for respiratory chain complexes, aconitase, and many other mitochondrial enzymes.
• Defects in the complex cause mitochondrial disorders, including Friedreich ataxia and ISCU myopathy.
• The complex is regulated by the mitochondrial iron-sulfur cluster assembly (ISC) machinery and interacts with the respiratory chain assembly pathway.
• CRISPR knockout, point mutation, knock-in, and overexpression models are key tools to dissect its function and disease relevance.
Description
The mitochondrial [2Fe-2S] assembly complex (GO:0099128) is a cellular component that catalyzes the formation of 2Fe-2S clusters within mitochondria. Iron-sulfur clusters are ancient, versatile cofactors required for electron transfer, enzymatic catalysis, and regulatory sensing. In humans, the core assembly complex comprises the scaffold protein ISCU, the cysteine desulfurase NFS1, the accessory protein LYRM4, the acyl carrier protein NDUFAB1, and frataxin (FXN). This complex is the entry point for mitochondrial iron-sulfur cluster biogenesis, and its products are delivered to dozens of recipient proteins, including subunits of respiratory complexes I, II, and III, aconitase, and lipoic acid synthase. Because of its central role, dysfunction of the complex leads to severe mitochondrial diseases, and it is a focus of research in metabolism, neurodegeneration, and cancer. Understanding its structure, regulation, and disease links requires precise genetic models and functional assays.
mitochondrial [2Fe-2S] assembly complex At A Glance
| GO ID | GO:0099128 |
|---|---|
| GO term | mitochondrial [2Fe-2S] assembly complex |
| Ontology | cellular_component |
| Synonym | mitochondrial iron-sulfur cluster assembly complex; mitochondrial ISCU complex |
| Major function | Formation of 2Fe-2S clusters in mitochondria |
| Subunits (human) | ISCU, NFS1, LYRM4, NDUFAB1, FXN |
| Cellular location | Mitochondrial matrix |
| Associated process | Iron-sulfur cluster assembly and respiratory chain biogenesis |
What Is GO:0099128?
GO:0099128 describes a protein complex located in mitochondria that is capable of forming 2Fe-2S clusters. In humans, this complex is composed of ISCU, NFS1, LYRM4, NDUFAB1, and FXN. It is also known as the mitochondrial iron-sulfur cluster assembly complex or mitochondrial ISCU complex. The complex provides the scaffold and enzymatic machinery for the initial steps of iron-sulfur cluster biosynthesis in the mitochondrial matrix.
Why Is mitochondrial [2Fe-2S] assembly complex Important in Cell Biology?
The mitochondrial [2Fe-2S] assembly complex is essential for life because it produces iron-sulfur clusters that are indispensable for mitochondrial respiration, iron homeostasis, and numerous metabolic pathways. Mutations in its components cause devastating diseases such as Friedreich ataxia and ISCU myopathy, and its dysfunction is implicated in cancer and neurodegeneration. Studying this complex provides insights into mitochondrial biology and offers targets for therapeutic intervention.
• Produces 2Fe-2S clusters required for electron transfer in respiratory complexes I, II, and III.
• Supplies clusters to aconitase, lipoic acid synthase, and other mitochondrial enzymes.
• Mutations in FXN cause Friedreich ataxia, a neurodegenerative disorder.
• Mutations in ISCU cause hereditary myopathy with exercise intolerance.
• Dysregulation is linked to cancer metabolism and tumor growth.
• Interacts with the mitochondrial import and assembly machinery.
• Is a target for therapies aimed at boosting mitochondrial function.
• Its assembly is coordinated with respiratory chain supercomplex formation.
• Provides a model for studying iron-sulfur cluster trafficking.
• CRISPR screens can identify modifiers of its function.
What Happens During mitochondrial [2Fe-2S] assembly complex?
Cysteine Desulfurization by NFS1
In simple terms: NFS1 takes sulfur from cysteine and passes it on.
NFS1 is a pyridoxal phosphate-dependent cysteine desulfurase that abstracts sulfur from L-cysteine to form a persulfide intermediate. This step is the sulfur source for cluster assembly. NFS1 activity is enhanced by LYRM4 (also known as ISD11) and is coupled to the scaffold ISCU.
Scaffold Assembly on ISCU
In simple terms: ISCU holds the iron and sulfur atoms together to form a cluster.
ISCU serves as the scaffold upon which 2Fe-2S clusters are assembled. It receives sulfur from NFS1 and iron from frataxin (FXN), which acts as an iron chaperone or regulator. The cluster is transiently coordinated by conserved cysteine residues on ISCU before being transferred to recipient proteins.
Role of Frataxin (FXN) in Iron Delivery
In simple terms: Frataxin helps deliver iron to the assembly site.
FXN is a mitochondrial protein that binds iron and interacts with the NFS1-ISCU-LYRM4 complex. It is proposed to regulate the rate of cluster assembly and to provide iron in a bioavailable form. Loss of FXN leads to decreased cluster formation and mitochondrial iron overload.
Acyl Carrier Protein NDUFAB1
In simple terms: NDUFAB1 is a small protein that may help stabilize the complex.
NDUFAB1 (also known as ACP) is a mitochondrial acyl carrier protein that is part of the complex. It is thought to play a structural or regulatory role, possibly linking cluster assembly to fatty acid synthesis. Its exact function in the complex is still under investigation.
Cluster Transfer to Recipient Proteins
In simple terms: The finished cluster is handed off to other proteins that need it.
After assembly on ISCU, the 2Fe-2S cluster is transferred to recipient apoproteins via chaperone systems such as HSC20 and GRP75. These recipients include respiratory chain subunits, aconitase, and lipoic acid synthase. Defects in transfer lead to impaired mitochondrial function.
Key Genes Involved in GO:0099128 mitochondrial [2Fe-2S] assembly complex
The following genes encode components or regulators of the mitochondrial [2Fe-2S] assembly complex and are frequently studied in mitochondrial biology.
| Gene | Major Role | Research Relevance |
|---|---|---|
| ISCU | Scaffold for 2Fe-2S cluster assembly | Mutations cause myopathy; target for functional studies |
| NFS1 | Cysteine desulfurase providing sulfur | Essential for cluster assembly; knockout is lethal |
| LYRM4 | Accessory protein stabilizing NFS1 | Required for NFS1 activity; mutations affect assembly |
| NDUFAB1 | Acyl carrier protein component | Structural role; links to complex I assembly |
| FXN | Iron chaperone/regulator | Mutations cause Friedreich ataxia |
| HSC20 | Chaperone for cluster transfer | Facilitates transfer to recipient proteins |
| GRP75 | Mitochondrial chaperone | Assists in cluster transfer and protein folding |
| FDX1 | Ferredoxin involved in cluster assembly | Provides electrons for sulfur reduction |
| FDXR | Ferredoxin reductase | Supplies electrons to FDX1 |
| GLRX5 | Glutaredoxin involved in cluster transfer | Facilitates 2Fe-2S cluster transfer |
| ABCB7 | Mitochondrial iron exporter | Links cluster assembly to iron homeostasis |
| ISCU1 | Isoform of ISCU | Tissue-specific roles in cluster assembly |
| ISCU2 | Isoform of ISCU | Muscle-specific isoform affected in myopathy |
| NFS1 | Cysteine desulfurase | Target for cancer metabolism studies |
| LYRM4 | Accessory protein | Mutations cause mitochondrial disorder |
| NDUFAB1 | Acyl carrier protein | Component of complex I and assembly complex |
| FXN | Frataxin | Therapeutic target for Friedreich ataxia |
| HSC20 | Co-chaperone | Required for cluster transfer to iron-sulfur proteins |
How Is mitochondrial [2Fe-2S] assembly complex Regulated?
The mitochondrial [2Fe-2S] assembly complex is regulated at multiple levels. Its expression is controlled by the mitochondrial unfolded protein response (UPRmt) and by iron-sulfur cluster assembly regulators such as ISR (integrated stress response). The availability of iron and cysteine, as well as the redox state of the mitochondria, influences complex activity. Additionally, the complex interacts with the respiratory chain assembly machinery, and its function is coordinated with mitochondrial protein import and supercomplex formation.
mitochondrial [2Fe-2S] assembly complex and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| FXN | Friedreich ataxia | Knockout or knock-in of expanded GAA repeats in iPSCs |
| ISCU | Hereditary myopathy | Point mutation knock-in in mouse models |
| NFS1 | Cancer dependency | CRISPR knockout in cancer cell lines |
| LYRM4 | Mitochondrial disorder | Knockout in patient fibroblasts |
| NDUFAB1 | Complex I deficiency | Knockout in HEK293 cells |
Friedreich Ataxia
Friedreich ataxia is caused by reduced levels of frataxin (FXN), a component of the mitochondrial [2Fe-2S] assembly complex. Loss of FXN leads to decreased iron-sulfur cluster biogenesis, mitochondrial iron accumulation, and oxidative stress, resulting in neurodegeneration and cardiomyopathy.
ISCU Myopathy
Mutations in ISCU cause hereditary myopathy with exercise intolerance. These mutations impair the scaffold function of ISCU, leading to reduced cluster assembly in muscle and severe metabolic consequences.
Cancer Metabolism
The mitochondrial [2Fe-2S] assembly complex is upregulated in some cancers to support increased metabolic demands. Targeting NFS1 or other components has been proposed as a therapeutic strategy, and CRISPR screens have identified dependencies.
Neurodegeneration
Defects in iron-sulfur cluster assembly are linked to neurodegenerative diseases beyond Friedreich ataxia, including Parkinson's and Alzheimer's disease, where mitochondrial dysfunction and iron dyshomeostasis are common features.
From mitochondrial [2Fe-2S] assembly complex-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| Does ISCU mutation affect cluster assembly? | Point mutation knock-in in cell lines |
| What is the role of FXN in iron delivery? | FXN knockout and overexpression models |
| Can NFS1 be targeted in cancer? | CRISPR knockout in cancer cells |
| How does the complex interact with respiratory chain? | Tagged knock-in for proteomics |
| What are the dynamics of cluster transfer? | Overexpression of tagged ISCU and live-cell imaging |
| Is LYRM4 required for NFS1 stability? | Knockout and rescue experiments |
How to Study the mitochondrial [2Fe-2S] assembly complex Process
| Method | What It Measures | Typical Application |
|---|---|---|
| CRISPR knockout screens | Gene essentiality and modifiers | Identify novel regulators of cluster assembly |
| AP-MS | Protein-protein interactions | Define complex composition and dynamics |
| Isotope tracing | Sulfur and iron flux | Quantify cluster assembly activity |
| Live-cell imaging | Complex localization and dynamics | Study assembly in real time |
| RNA-seq | Transcriptional changes | Assess UPRmt and iron homeostasis |
| Ribo-seq | Translation efficiency | Measure synthesis of complex components |
| Seahorse respirometry | Mitochondrial respiration | Functional impact of complex mutations |
| Blue native PAGE | Complex integrity and supercomplexes | Analyze assembly and respiratory chain |
CRISPR-Cas9 Knockout Screens
Genome-wide CRISPR knockout screens can identify genes that are essential for the function of the mitochondrial [2Fe-2S] assembly complex or that modify its activity. Such screens have revealed dependencies on NFS1 and other components in cancer cells.
Proteomics and Interactomics
Affinity purification coupled to mass spectrometry (AP-MS) of tagged complex subunits (e.g., ISCU, NFS1) can define the interactome and identify dynamic partners. This approach has been used to map the assembly complex and its clients.
Metabolic and Isotope Tracing
Isotope tracing with 34S-cysteine or 55Fe can measure flux through the cluster assembly pathway. These methods quantify the incorporation of sulfur and iron into recipient proteins and assess complex activity.
Imaging and Live-Cell Assays
Fluorescently tagged ISCU or FXN can be used to visualize the complex in live cells. Mitochondrial morphology and iron levels can be monitored using dyes and genetically encoded sensors.
How CRISPR Can Be Used to Study GO:0099128 mitochondrial [2Fe-2S] assembly complex
Knockout
CRISPR knockout of ISCU, NFS1, LYRM4, NDUFAB1, or FXN can abolish complex function, leading to impaired respiration and cell death. These models are used to study the essentiality of each subunit and to identify compensatory pathways.
Point Mutation
Point mutations that mimic patient alleles (e.g., ISCU G50E) can be introduced via CRISPR to study the molecular basis of disease. Such models reveal subtle defects in cluster assembly and transfer.
Knock-in
Knock-in of tagged versions (e.g., HA-ISCU) allows for affinity purification and imaging. Knock-in of disease-associated mutations or regulatory elements can model human disorders in cells and animals.
Overexpression
Overexpression of complex components or FXN can rescue defects or exacerbate phenotypes. CRISPR activation (CRISPRa) can be used to upregulate endogenous genes for gain-of-function studies.
How EDITGENE Supports mitochondrial [2Fe-2S] assembly complex Research
Researchers studying mitochondrial [2Fe-2S] assembly complex-related genes often need to determine whether a candidate gene is causally involved in cluster assembly, respiratory chain function, or disease. EDITGENE provides a comprehensive suite of CRISPR services to generate precisely engineered cell models for such investigations.
Contact EDITGENE today to design your custom CRISPR model for mitochondrial [2Fe-2S] assembly complex research.
Frequently Asked Questions About mitochondrial [2Fe-2S] assembly complex
What is the mitochondrial [2Fe-2S] assembly complex?
It is a protein complex in mitochondria that builds 2Fe-2S iron-sulfur clusters, composed of ISCU, NFS1, LYRM4, NDUFAB1, and FXN in humans.
What genes are involved in the mitochondrial [2Fe-2S] assembly complex?
The core genes are ISCU, NFS1, LYRM4, NDUFAB1, and FXN, with additional factors like HSC20, GRP75, FDX1, and GLRX5 assisting in cluster transfer.
What is the function of GO:0099128?
GO:0099128 defines a cellular component that catalyzes the formation of 2Fe-2S clusters in mitochondria, essential for respiratory chain and metabolic enzymes.
Which diseases are linked to the mitochondrial [2Fe-2S] assembly complex?
Mutations in FXN cause Friedreich ataxia, and mutations in ISCU cause hereditary myopathy; the complex is also implicated in cancer and neurodegeneration.
How is the mitochondrial [2Fe-2S] assembly complex regulated?
It is regulated by iron and cysteine availability, the mitochondrial unfolded protein response, and interactions with the respiratory chain assembly machinery.
What methods are used to study the mitochondrial [2Fe-2S] assembly complex?
Common methods include CRISPR knockout screens, affinity purification mass spectrometry, isotope tracing, live-cell imaging, and respirometry.
Can CRISPR be used to model mitochondrial [2Fe-2S] assembly complex diseases?
Yes, CRISPR knockout, point mutation knock-in, and tagged knock-in models are widely used to study disease mechanisms and test therapies.
What is the role of frataxin in the mitochondrial [2Fe-2S] assembly complex?
Frataxin (FXN) is an iron-binding protein that regulates iron delivery to the complex and is mutated in Friedreich ataxia.
What is the role of NFS1 in the mitochondrial [2Fe-2S] assembly complex?
NFS1 is a cysteine desulfurase that provides sulfur for cluster assembly and is essential for the complex function.
How does the mitochondrial [2Fe-2S] assembly complex interact with the respiratory chain?
The clusters produced are inserted into respiratory chain subunits, and the complex physically and functionally interacts with respiratory chain assembly factors.
Conclusion
The mitochondrial [2Fe-2S] assembly complex (GO:0099128) is a central hub for iron-sulfur cluster biogenesis in mitochondria, with critical roles in respiration, metabolism, and disease. Its components, including ISCU, NFS1, LYRM4, NDUFAB1, and FXN, are the subject of intense research because of their links to Friedreich ataxia, myopathy, and cancer. Advanced CRISPR models and multi-omics approaches are essential to unravel its mechanisms and to develop targeted therapies. EDITGENE provides the tools and expertise to accelerate this research.
References
- 1. Vercellino I et al.. 2022. The assembly, regulation and function of the mitochondrial respiratory chain.. Nat Rev Mol Cell Biol 23(2):141-161 PMID: 34621061
- 2. Fernandez-Vizarra E et al.. 2021. Mitochondrial disorders of the OXPHOS system.. FEBS Lett 595(8):1062-1106 PMID: 33159691
- 3. Stroud DA et al.. 2016. Accessory subunits are integral for assembly and function of human mitochondrial complex I.. Nature 538(7623):123-126 PMID: 27626371
- 4. Fung TS et al.. 2023. The multiple links between actin and mitochondria.. Nat Rev Mol Cell Biol 24(9):651-667 PMID: 37277471
- 5. Tang JX et al.. 2020. Mitochondrial OXPHOS Biogenesis: Co-Regulation of Protein Synthesis, Import, and Assembly Pathways.. Int J Mol Sci 21(11) PMID: 32481479
- 6. Guan S et al.. 2022. Mitochondrial Respiratory Chain Supercomplexes: From Structure to Function.. Int J Mol Sci 23(22) PMID: 36430359
- 7. Guo R et al.. 2018. Structure and mechanism of mitochondrial electron transport chain.. Biomed J 41(1):9-20 PMID: 29673555
- 8. Zheng W et al.. 2024. High-resolution in situ structures of mammalian respiratory supercomplexes.. Nature 631(8019):232-239 PMID: 38811722
