Existing Annotations Review

GO Term	Evidence	Action	Reason
GO:0005739 mitochondrion	IBA GO_REF:0000033	ACCEPT	Summary: NFU1 is established as a mitochondrial protein through multiple lines of evidence. The IBA annotation from phylogenetic analysis is well-supported by direct experimental evidence showing mitochondrial localization of isoform I (PMID:12886008), mitochondrial matrix localization from Reactome pathway analysis, and high-confidence mitochondrial proteomics (PMID:34800366). Reason: Mitochondrial localization is a core feature of NFU1 function. The protein functions specifically in mitochondrial Fe-S cluster biogenesis and is targeted to the mitochondrial matrix (PMID:12886008, Reactome:R-HSA-6793591). This is the primary site of NFU1 function. Supporting Evidence: PMID:12886008 Isoform I is localized in the mitochondria, whereas isoform II is present in the cytosol and the nucleus. file:human/NFU1/NFU1-deep-research-falcon.md model: Edison Scientific Literature
GO:0051604 protein maturation	IBA GO_REF:0000033	MODIFY	Summary: NFU1 participates in the maturation of [4Fe-4S] cluster-containing proteins by delivering Fe-S clusters to target proteins. The IBA annotation reflects the conserved role of NFU family proteins in Fe-S protein maturation across species. Reason: While NFU1 does participate in protein maturation, the term "protein maturation" (GO:0051604) is too general. The specific role of NFU1 is in iron-sulfur cluster assembly and delivery to target proteins. The more specific process term GO:0016226 (iron-sulfur cluster assembly) better captures NFU1's function (PMID:12886008, PMID:28906594). Proposed replacements: iron-sulfur cluster assembly
GO:0051539 4 iron, 4 sulfur cluster binding	IBA GO_REF:0000033	ACCEPT	Summary: The IBA annotation for [4Fe-4S] cluster binding is strongly supported by direct biochemical evidence. Tong et al. (2003) demonstrated using UV-visible absorption and 57Fe Mossbauer spectroscopy that purified human Nfu assembles approximately one labile [4Fe-4S] cluster per two monomers (PMID:12886008). Wesley et al. (2017) further characterized [4Fe-4S] cluster binding and its disruption by disease-causing mutations (PMID:28906594). Reason: [4Fe-4S] cluster binding is the core molecular function of NFU1. The protein dimerizes and ligates a bridging [4Fe-4S] cluster that is subsequently delivered to target proteins. This has been demonstrated by multiple spectroscopic and biochemical studies. Supporting Evidence: PMID:12886008 The results suggest that Nfu can assemble approximately one labile [4Fe-4S] cluster per two Nfu monomers, and support the proposal that Nfu is an alternative scaffold protein for assembly of clusters that are subsequently used for maturation of targeted Fe-S proteins. PMID:28906594 iron-sulfur (Fe/S) cluster-containing proteins constitute one of the largest protein classes, with highly varied function...we have characterized the impact of defects occurring in the MMDS1 disease state that result from a point mutation (p.Gly189Arg) near the active site of NFU1, an Fe/S scaffold protein.
GO:0005506 iron ion binding	IEA GO_REF:0000002	ACCEPT	Summary: The IEA annotation for iron ion binding is derived from InterPro domain mapping (IPR001075). Direct experimental evidence supports iron binding as part of the [4Fe-4S] cluster (PMID:12886008). Reason: Iron ion binding is inherent to NFU1's function as an Fe-S cluster scaffold. The [4Fe-4S] cluster contains four iron atoms that are coordinated by the protein. While this is a more general term than [4Fe-4S] cluster binding, it is not incorrect and provides complementary information about metal binding capacity. Supporting Evidence: PMID:12886008 Nfu can assemble approximately one labile [4Fe-4S] cluster per two Nfu monomers
GO:0005739 mitochondrion	IEA GO_REF:0000044	ACCEPT	Summary: The IEA annotation from UniProtKB subcellular location mapping is consistent with direct experimental evidence. Multiple IDA annotations also support mitochondrial localization. Reason: While this duplicates the IBA annotation, the evidence source (UniProt subcellular location mapping) provides independent support. Mitochondrial localization is well-established.
GO:0005829 cytosol	IEA GO_REF:0000044	KEEP AS NON CORE	Summary: Cytosolic localization has experimental support from Tong et al. (2003) who showed that alternative splicing produces isoforms with distinct localizations - isoform II lacks the mitochondrial targeting sequence and localizes to cytosol and nucleus (PMID:12886008). Reason: While cytosolic localization is experimentally validated for isoform II, the primary function of NFU1 in iron-sulfur cluster biogenesis occurs in mitochondria. The cytosolic isoform represents an alternative localization that may have secondary functions. Supporting Evidence: PMID:12886008 Isoform I is localized in the mitochondria, whereas isoform II is present in the cytosol and the nucleus.
GO:0016226 iron-sulfur cluster assembly	IEA GO_REF:0000002	ACCEPT	Summary: The IEA annotation from InterPro (IPR001075) correctly identifies NFU1's role in iron-sulfur cluster assembly. This is strongly supported by direct experimental evidence (PMID:12886008, PMID:28906594). Reason: Iron-sulfur cluster assembly is the primary biological process in which NFU1 participates. NFU1 functions as a late-acting scaffold/carrier that assembles [4Fe-4S] clusters and delivers them to target proteins including LIAS. Supporting Evidence: PMID:12886008 Nfu is an alternative scaffold protein for assembly of clusters that are subsequently used for maturation of targeted Fe-S proteins.
GO:0046872 metal ion binding	IEA GO_REF:0000043	MARK AS OVER ANNOTATED	Summary: The IEA annotation from UniProt keyword mapping is very general. NFU1 binds iron as part of iron-sulfur clusters. Reason: While technically correct (NFU1 binds iron ions as part of the [4Fe-4S] cluster), this term is too general and uninformative. The more specific terms GO:0051539 (4 iron, 4 sulfur cluster binding) and GO:0005506 (iron ion binding) already capture this information with greater specificity.
GO:0051536 iron-sulfur cluster binding	IEA GO_REF:0000120	ACCEPT	Summary: The IEA annotation for general iron-sulfur cluster binding is correct but less specific than the [4Fe-4S] cluster binding term that is also annotated. Reason: This general term is acceptable as NFU1 can bind both [2Fe-2S] and [4Fe-4S] clusters during its function (PMID:27538573 shows [2Fe-2S] binding; PMID:12886008 shows [4Fe-4S]). The more general term captures this broader capacity. Supporting Evidence: PMID:27538573 Human holo Nfu shows a dimer-tetramer equilibrium with a protein to cluster ratio of 2:1, reflecting the Nfu-bridging [2Fe-2S] cluster.
GO:0005515 protein binding	IPI PMID:22190034 Global landscape of HIV-human protein complexes.	MARK AS OVER ANNOTATED	Summary: This annotation is from a large-scale HIV-human interactome study. The biological relevance of interactions detected in such studies for normal NFU1 function is unclear. Reason: The term "protein binding" is uninformative and does not capture the specific functional interactions of NFU1 with Fe-S biogenesis partners (BOLA3, HSPA9, ISCU, ISCA1). Large-scale interactome studies often detect interactions that may not be physiologically relevant. Supporting Evidence: PMID:22190034 Global landscape of HIV-human protein complexes.
GO:0005515 protein binding	IPI PMID:25416956 A proteome-scale map of the human interactome network.	MARK AS OVER ANNOTATED	Summary: This annotation is from a proteome-scale human interactome map. While demonstrating NFU1 interacts with other proteins, "protein binding" is uninformative. Reason: The generic "protein binding" term does not capture the biologically meaningful interactions of NFU1. More informative annotations would specify interactions with Fe-S cluster biogenesis components. Supporting Evidence: PMID:25416956 A proteome-scale map of the human interactome network.
GO:0005515 protein binding	IPI PMID:27532772 Mitochondrial Bol1 and Bol3 function as assembly factors for...	MODIFY	Summary: This reference (Uzarska et al. 2016, eLife) demonstrates specific interaction between NFU1 and BOLA3 as part of Fe-S cluster biogenesis. This is a biologically meaningful interaction showing BOLA3 preferentially interacts with holo-NFU1. Reason: While the IPI evidence for protein binding is valid, a more informative term could capture the specific functional role. However, without a specific GO term for "BOLA3 binding" or similar, this annotation provides evidence of a physiologically relevant interaction in Fe-S cluster transfer. Proposed replacements: iron-sulfur cluster chaperone activity Supporting Evidence: PMID:27532772 Preferential interaction of BOLA1 with holo-GLRX5 and of BOLA3 with holo-NFU1
GO:0005515 protein binding	IPI PMID:32296183 A reference map of the human binary protein interactome.	MARK AS OVER ANNOTATED	Summary: This annotation is from a reference map of the human binary protein interactome (HuRI). While detecting interactions, the generic term is uninformative for understanding NFU1 function. Reason: Large-scale interactome data, while valuable for network analysis, produces generic "protein binding" annotations that do not illuminate NFU1's specific role in Fe-S cluster biogenesis. Supporting Evidence: PMID:32296183 Apr 8. A reference map of the human binary protein interactome.
GO:0005829 cytosol	IDA GO_REF:0000052	KEEP AS NON CORE	Summary: The IDA from immunofluorescence curation (HPA) detects cytosolic signal. This is consistent with the existence of cytosolic isoform II. Reason: Cytosolic localization is validated but represents a secondary localization. The primary Fe-S cluster assembly function occurs in mitochondria.
GO:0005739 mitochondrion	HTP PMID:34800366 Quantitative high-confidence human mitochondrial proteome an...	ACCEPT	Summary: High-throughput mitochondrial proteomics study confirming NFU1 as a mitochondrial protein. This provides independent high-confidence support for mitochondrial localization. Reason: The quantitative high-confidence human mitochondrial proteome provides strong support for mitochondrial localization of NFU1. Supporting Evidence: PMID:34800366 Epub 2021 Nov 19. Quantitative high-confidence human mitochondrial proteome and its dynamics in cellular context.
GO:0051537 2 iron, 2 sulfur cluster binding	IDA PMID:27538573 Iron-sulfur cluster exchange reactions mediated by the human...	ACCEPT	Summary: Wachnowsky et al. (2016) demonstrated that human NFU1 can bind a [2Fe-2S] cluster as an intermediate during cluster transfer. The study characterized cluster exchange chemistry and showed NFU1 can accept [2Fe-2S] clusters and transfer them to ferredoxins. Reason: The [2Fe-2S] cluster binding capacity is experimentally demonstrated and represents an intermediate state in the cluster maturation pathway. NFU1 receives [2Fe-2S] units from donors that are subsequently converted to [4Fe-4S] clusters. Supporting Evidence: PMID:27538573 Herein, we characterize the cluster exchange chemistry of human Nfu and its capacity to bind and transfer a [2Fe-2S] cluster
GO:0051604 protein maturation	IDA PMID:27538573 Iron-sulfur cluster exchange reactions mediated by the human...	MODIFY	Summary: The IDA annotation for protein maturation from this reference reflects NFU1's role in maturing Fe-S proteins by delivering clusters. However, the term is generic. Reason: While NFU1 does contribute to protein maturation, the specific process is iron-sulfur cluster assembly and delivery. The term GO:0016226 (iron-sulfur cluster assembly) more precisely captures NFU1's role. Proposed replacements: iron-sulfur cluster assembly Supporting Evidence: PMID:27538573 Epub 2016 Aug 18. Iron-sulfur cluster exchange reactions mediated by the human Nfu protein.
GO:0005515 protein binding	IPI PMID:26702583 Mitochondrial Hspa9/Mortalin regulates erythroid differentia...	MODIFY	Summary: Shan & Cortopassi (2016) demonstrated that HSPA9/Mortalin interacts with NFU1 as part of the mitochondrial Fe-S cluster biogenesis machinery. This is a functionally relevant interaction. Reason: While "protein binding" is too generic, this reference documents a biologically meaningful interaction. HSPA9 is the mitochondrial chaperone that works with the co-chaperone HSC20 in Fe-S cluster transfer. A more specific molecular function term capturing scaffold activity would be more informative. Proposed replacements: iron-sulfur cluster chaperone activity Supporting Evidence: PMID:26702583 HSPA9 interacts with and stabilizes the mitochondrial ISC biogenesis proteins frataxin, Nfs1, ISCU, and Nfu.
GO:0016226 iron-sulfur cluster assembly	IDA PMID:28906594 Understanding the molecular basis for multiple mitochondrial...	ACCEPT	Summary: Wesley et al. (2017) characterized NFU1's role in Fe-S cluster assembly and how the disease-causing G189R mutation impairs this function. The study directly demonstrates NFU1's function as an Fe-S scaffold protein. Reason: This is strong direct experimental evidence for NFU1's role in iron-sulfur cluster assembly. The paper shows that pathogenic mutations impair NFU1's ability to receive and transfer Fe-S clusters. Supporting Evidence: PMID:28906594 substitution at position 189 triggers structural changes that increase flexibility, decrease stability, and alter the monomer-dimer equilibrium toward monomer, thereby impairing the ability of the Gly189X derivatives to receive an Fe/S cluster from physiologically relevant sources.
GO:0051539 4 iron, 4 sulfur cluster binding	IDA PMID:28906594 Understanding the molecular basis for multiple mitochondrial...	ACCEPT	Summary: Direct experimental evidence from MMDS1 disease characterization confirms [4Fe-4S] cluster binding by NFU1. The pathogenic G189R variant disrupts this capacity. Reason: This provides disease-relevant experimental validation of [4Fe-4S] cluster binding as a core function of NFU1. Supporting Evidence: PMID:28906594 we have characterized the impact of defects occurring in the MMDS1 disease state that result from a point mutation (p.Gly189Arg) near the active site of NFU1, an Fe/S scaffold protein.
GO:0005759 mitochondrial matrix	TAS Reactome:R-HSA-6793591	ACCEPT	Summary: The Reactome pathway for protein lipoylation places NFU1 in the mitochondrial matrix, where it functions to deliver [4Fe-4S] clusters to LIAS for lipoyl-GCSH synthesis. Reason: Mitochondrial matrix localization is more specific than general mitochondrion annotation and reflects the actual site of NFU1 function in Fe-S cluster delivery to LIAS and other matrix clients.
GO:0005829 cytosol	IDA PMID:12915448 The Lafora disease gene product laforin interacts with HIRIP...	KEEP AS NON CORE	Summary: Ganesh et al. (2003) identified NFU1 (as HIRIP5) as a cytosolic protein that interacts with laforin. This reflects the cytosolic isoform. Reason: This provides additional experimental evidence for cytosolic localization of one NFU1 isoform. However, the mitochondrial isoform is the primary functional form for Fe-S cluster biogenesis. Supporting Evidence: PMID:12915448 HIRIP5 encodes a cytosolic protein and is expressed ubiquitously, perhaps reflecting a house-keeping function.
GO:0005506 iron ion binding	IDA PMID:12886008 Subcellular compartmentalization of human Nfu, an iron-sulfu...	ACCEPT	Summary: Tong et al. (2003) directly demonstrated iron binding through spectroscopic analysis of purified NFU1 with assembled Fe-S clusters. Reason: Direct experimental evidence from Mossbauer spectroscopy and UV-visible absorption confirms iron binding as part of [4Fe-4S] cluster assembly. Supporting Evidence: PMID:12886008 A combination of biochemical and spectroscopic techniques, including UV-visible absorption and 57Fe Mössbauer spectroscopies, have been used to investigate the ability of purified human Nfu to assemble Fe-S clusters
GO:0005634 nucleus	IDA PMID:12886008 Subcellular compartmentalization of human Nfu, an iron-sulfu...	KEEP AS NON CORE	Summary: Tong et al. (2003) showed that isoform II (lacking mitochondrial targeting sequence) localizes to nucleus in addition to cytosol. Reason: Nuclear localization is documented for isoform II but represents a secondary localization. The functional significance of nuclear NFU1 is not well established. Supporting Evidence: PMID:12886008 Isoform I is localized in the mitochondria, whereas isoform II is present in the cytosol and the nucleus.
GO:0005739 mitochondrion	IDA PMID:12886008 Subcellular compartmentalization of human Nfu, an iron-sulfu...	ACCEPT	Summary: Foundational experimental study demonstrating mitochondrial localization of NFU1 isoform I and its ability to assemble [4Fe-4S] clusters. Reason: Primary experimental evidence establishing mitochondrial localization of the functional isoform of NFU1. Supporting Evidence: PMID:12886008 Isoform I is localized in the mitochondria, whereas isoform II is present in the cytosol and the nucleus.
GO:0005829 cytosol	IDA PMID:12886008 Subcellular compartmentalization of human Nfu, an iron-sulfu...	KEEP AS NON CORE	Summary: Tong et al. (2003) demonstrated cytosolic localization of NFU1 isoform II. Reason: Cytosolic localization is documented for isoform II. This represents secondary localization relative to the mitochondrial function. Supporting Evidence: PMID:12886008 Isoform I is localized in the mitochondria, whereas isoform II is present in the cytosol and the nucleus.
GO:0016226 iron-sulfur cluster assembly	IDA PMID:12886008 Subcellular compartmentalization of human Nfu, an iron-sulfu...	ACCEPT	Summary: This is the foundational study establishing NFU1 as an iron-sulfur cluster scaffold protein capable of assembling [4Fe-4S] clusters for delivery to target proteins. Reason: Primary experimental evidence defining NFU1's core biological function in Fe-S cluster assembly. This study established the role of human Nfu as an alternative scaffold in the Fe-S biogenesis pathway. Supporting Evidence: PMID:12886008 support the proposal that Nfu is an alternative scaffold protein for assembly of clusters that are subsequently used for maturation of targeted Fe-S proteins.
GO:0051539 4 iron, 4 sulfur cluster binding	IDA PMID:12886008 Subcellular compartmentalization of human Nfu, an iron-sulfu...	ACCEPT	Summary: The foundational demonstration that NFU1 binds [4Fe-4S] clusters using Mossbauer spectroscopy and biochemical analysis. Reason: This provides the primary experimental evidence for [4Fe-4S] cluster binding, which is the core molecular function of NFU1. Supporting Evidence: PMID:12886008 The results suggest that Nfu can assemble approximately one labile [4Fe-4S] cluster per two Nfu monomers
GO:0140132 iron-sulfur cluster chaperone activity	IDA PMID:12886008 Subcellular compartmentalization of human Nfu, an iron-sulfu...	NEW	Summary: NFU1 functions as an iron-sulfur cluster chaperone, assembling [4Fe-4S] clusters and delivering them to target proteins. This molecular function term captures the core activity of NFU1 better than "protein binding". Reason: This term specifically captures NFU1's role as a late-acting Fe-S cluster chaperone that assembles clusters from [2Fe-2S] intermediates and delivers them to client proteins including LIAS. This is the defining molecular function of NFU1. Supporting Evidence: PMID:12886008 support the proposal that Nfu is an alternative scaffold protein for assembly of clusters that are subsequently used for maturation of targeted Fe-S proteins. PMID:27538573 Human Nfu is an iron-sulfur cluster protein that has recently been implicated in multiple mitochondrial dysfunctional syndrome PMID:28906594 Understanding the molecular basis for multiple mitochondrial dysfunctions syndrome 1 (MMDS1): impact of a disease-causing Gly189Arg substitution on NFU1.

Core Functions

NFU1 is a late-acting [4Fe-4S] cluster chaperone that receives [2Fe-2S] clusters from upstream donors ISCU2 and ISCA1, assembles them into [4Fe-4S] clusters, and delivers these to target proteins. This chaperone function is demonstrated by biochemical reconstitution, spectroscopic analysis, and functional complementation studies (PMID:12886008, PMID:27538573, PMID:28906594).

Molecular Function:

iron-sulfur cluster chaperone activity

Directly Involved In:

iron-sulfur cluster assembly

Cellular Locations:

mitochondrial matrix

NFU1 dimerizes and ligates a bridging [4Fe-4S] cluster. Mossbauer spectroscopy and UV-visible absorption studies demonstrate approximately one [4Fe-4S] cluster per two NFU1 monomers (PMID:12886008). The cluster-binding cysteines (C210 and C213) are essential for function and are disrupted by pathogenic mutations (PMID:28906594).

Molecular Function:

4 iron, 4 sulfur cluster binding

Cellular Locations:

mitochondrial matrix

References

GO_REF:0000002

Gene Ontology annotation through association of InterPro records with GO terms

GO_REF:0000033

Annotation inferences using phylogenetic trees

GO_REF:0000043

Gene Ontology annotation based on UniProtKB/Swiss-Prot keyword mapping

GO_REF:0000044

Gene Ontology annotation based on UniProtKB/Swiss-Prot Subcellular Location vocabulary mapping, accompanied by conservative changes to GO terms applied by UniProt

GO_REF:0000052

Gene Ontology annotation based on curation of immunofluorescence data

GO_REF:0000120

Combined Automated Annotation using Multiple IEA Methods

PMID:12886008

Subcellular compartmentalization of human Nfu, an iron-sulfur cluster scaffold protein, and its ability to assemble a [4Fe-4S] cluster.

NFU1 assembles approximately one [4Fe-4S] cluster per two monomers
Isoform I localizes to mitochondria; isoform II to cytosol and nucleus
Alternative splicing produces isoforms with distinct subcellular localizations

PMID:12915448

The Lafora disease gene product laforin interacts with HIRIP5, a phylogenetically conserved protein containing a NifU-like domain.

NFU1 (HIRIP5) identified as cytosolic protein
Interacts with laforin through its C-terminal NifU-like domain

PMID:22190034

Global landscape of HIV-human protein complexes.

PMID:25416956

A proteome-scale map of the human interactome network.

PMID:26702583

Mitochondrial Hspa9/Mortalin regulates erythroid differentiation via iron-sulfur cluster assembly.

HSPA9 interacts with NFU1 as part of mitochondrial ISC biogenesis machinery
NFU1 is stabilized by HSPA9 interaction

PMID:27532772

Mitochondrial Bol1 and Bol3 function as assembly factors for specific iron-sulfur proteins.

BOLA3 preferentially interacts with holo-NFU1
NFU1 and BOL proteins have distinct but overlapping functions in Fe-S protein maturation

PMID:27538573

Iron-sulfur cluster exchange reactions mediated by the human Nfu protein.

NFU1 binds [2Fe-2S] cluster as dimer with 2:1 protein to cluster ratio
Cluster can be transferred to apo ferredoxins at relatively fast rates
NFU1 implicated in MMDS1

PMID:28906594

Understanding the molecular basis for multiple mitochondrial dysfunctions syndrome 1 (MMDS1): impact of a disease-causing Gly189Arg substitution on NFU1.

G189R mutation alters protein structure and monomer-dimer equilibrium
Disease mutations impair ability to receive Fe-S clusters from donors

PMID:32296183

A reference map of the human binary protein interactome.

PMID:34800366

Quantitative high-confidence human mitochondrial proteome and its dynamics in cellular context.

NFU1 confirmed as high-confidence mitochondrial protein

Reactome:R-HSA-6793591

LIAS synthesizes lipoyl-GCSH

NFU1 provides [4Fe-4S] cluster to LIAS in mitochondrial matrix
Required for lipoylation pathway

file:human/NFU1/NFU1-deep-research-falcon.md

Deep research report on NFU1

Suggested Experiments

Experiment: Proteomics identification of all NFU1-dependent [4Fe-4S] client proteins

Experiment: Characterization of cytosolic isoform II function in CIA pathway

Experiment: Structure determination of NFU1 in complex with client proteins

Experiment: In vivo validation of METTL17 as an NFU1 client for mitoribosome biogenesis

📚 Additional Documentation

Deep Research Falcon

(NFU1-deep-research-falcon.md)

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gene_id: NFU1
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uniprot_accession: Q9UMS0
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AltName: Full=HIRA-interacting protein 5 {ECO:0000303|PubMed:11342215}; Flags:
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gene_info: Name=NFU1; Synonyms=HIRIP5 {ECO:0000303|PubMed:11342215}; ORFNames=CGI-33
{ECO:0000303|PubMed:10810093};
organism_full: Homo sapiens (Human).
protein_family: Belongs to the NifU family. .
protein_domains: FSCA_dom_sf. (IPR034904); Nfu/NifU_N. (IPR014824); Nfu/NifU_N_sf.
(IPR036498); NIF_FeS_clus_asmbl_NifU_C. (IPR001075); Nfu_N (PF08712)
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Question

Gene Research for Functional Annotation

⚠️ CRITICAL: Gene/Protein Identification Context

BEFORE YOU BEGIN RESEARCH: You MUST verify you are researching the CORRECT gene/protein. Gene symbols can be ambiguous, especially for less well-characterized genes from non-model organisms.

Target Gene/Protein Identity (from UniProt):

UniProt Accession: Q9UMS0
Protein Description: RecName: Full=NFU1 iron-sulfur cluster scaffold homolog, mitochondrial; AltName: Full=HIRA-interacting protein 5 {ECO:0000303|PubMed:11342215}; Flags: Precursor;
Gene Information: Name=NFU1; Synonyms=HIRIP5 {ECO:0000303|PubMed:11342215}; ORFNames=CGI-33 {ECO:0000303|PubMed:10810093};
Organism (full): Homo sapiens (Human).
Protein Family: Belongs to the NifU family. .
Key Domains: FSCA_dom_sf. (IPR034904); Nfu/NifU_N. (IPR014824); Nfu/NifU_N_sf. (IPR036498); NIF_FeS_clus_asmbl_NifU_C. (IPR001075); Nfu_N (PF08712)

MANDATORY VERIFICATION STEPS:

Check if the gene symbol "NFU1" matches the protein description above
Verify the organism is correct: Homo sapiens (Human).
Check if protein family/domains align with what you find in literature
If you find literature for a DIFFERENT gene with the same or similar symbol, STOP

If Gene Symbol is Ambiguous or You Cannot Find Relevant Literature:

DO NOT PROCEED WITH RESEARCH ON A DIFFERENT GENE. Instead:
- State clearly: "The gene symbol 'NFU1' is ambiguous or literature is limited for this specific protein"
- Explain what you found (e.g., "Found extensive literature on a different gene with the same symbol in a different organism")
- Describe the protein based ONLY on the UniProt information provided above
- Suggest that the protein function can be inferred from domain/family information

Research Target:

Please provide a comprehensive research report on the gene NFU1 (gene ID: NFU1, UniProt: Q9UMS0) in human.

The research report should be a detailed narrative explaining the function, biological processes, and localization of the gene product. Citations should be given for all claims.

You should prioritize authoritative reviews and primary scientific literature when conducting research. You can supplement
this with annotations you find in gene/protein databases, but these can be outdated or inaccurate.

We are specifically interested in the primary function of the gene - for enzymes, what reaction is catalyzed, and what is the substrate specificity? For transporters, what is the substrate? For structural proteins or adapters, what is the broader structural role? For signaling molecules, what is the role in the pathway.

We are interested in where in or outside the cell the gene product carries out its function.

We are also interested in the signaling or biochemical pathways in which the gene functions. We are less interested in broad pleiotropic effects, except where these elucidate the precise role.

Include evidence where possible. We are interested in both experimental evidence as well as inference from structure, evolution, or bioinformatic analysis. Precise studies should be prioritized over high-throughput, where available.

Output

Question: You are an expert researcher providing comprehensive, well-cited information.

Provide detailed information focusing on:
1. Key concepts and definitions with current understanding
2. Recent developments and latest research (prioritize 2023-2024 sources)
3. Current applications and real-world implementations
4. Expert opinions and analysis from authoritative sources
5. Relevant statistics and data from recent studies

Format as a comprehensive research report with proper citations. Include URLs and publication dates where available.
Always prioritize recent, authoritative sources and provide specific citations for all major claims.

Gene Research for Functional Annotation

⚠️ CRITICAL: Gene/Protein Identification Context

BEFORE YOU BEGIN RESEARCH: You MUST verify you are researching the CORRECT gene/protein. Gene symbols can be ambiguous, especially for less well-characterized genes from non-model organisms.

Target Gene/Protein Identity (from UniProt):

UniProt Accession: Q9UMS0
Protein Description: RecName: Full=NFU1 iron-sulfur cluster scaffold homolog, mitochondrial; AltName: Full=HIRA-interacting protein 5 {ECO:0000303|PubMed:11342215}; Flags: Precursor;
Gene Information: Name=NFU1; Synonyms=HIRIP5 {ECO:0000303|PubMed:11342215}; ORFNames=CGI-33 {ECO:0000303|PubMed:10810093};
Organism (full): Homo sapiens (Human).
Protein Family: Belongs to the NifU family. .
Key Domains: FSCA_dom_sf. (IPR034904); Nfu/NifU_N. (IPR014824); Nfu/NifU_N_sf. (IPR036498); NIF_FeS_clus_asmbl_NifU_C. (IPR001075); Nfu_N (PF08712)

MANDATORY VERIFICATION STEPS:

Check if the gene symbol "NFU1" matches the protein description above
Verify the organism is correct: Homo sapiens (Human).
Check if protein family/domains align with what you find in literature
If you find literature for a DIFFERENT gene with the same or similar symbol, STOP

If Gene Symbol is Ambiguous or You Cannot Find Relevant Literature:

Research Target:

Please provide a comprehensive research report on the gene NFU1 (gene ID: NFU1, UniProt: Q9UMS0) in human.

The research report should be a detailed narrative explaining the function, biological processes, and localization of the gene product. Citations should be given for all claims.

We are interested in where in or outside the cell the gene product carries out its function.

We are also interested in the signaling or biochemical pathways in which the gene functions. We are less interested in broad pleiotropic effects, except where these elucidate the precise role.

Research plan and verification
We verified the target as human NFU1 (UniProt Q9UMS0), a mitochondrial member of the NifU/NFU protein family that functions as a late-acting [4Fe–4S] cluster carrier in mitochondrial iron–sulfur (Fe–S) biogenesis. Literature confirms mitochondrial localization, NifU/Nfu domain architecture, and roles in late Fe–S delivery, with direct implications for MMDS1 and related phenotypes (Aug 2020 Human Molecular Genetics; Jan 2022 IUBMB Life) (jain2020assemblyofthe pages 3-4, maio2022mammalianironsulfur pages 7-9).

Comprehensive research report

1) Key concepts, definitions, and current understanding
- Identity and localization. NFU1 encodes a mitochondrial matrix protein of the NifU/NFU family with a degenerate N-terminal module and a conserved C‑terminal Nfu domain that ligates Fe–S clusters. Purified human NFU1 forms a dimer that binds a bridging [4Fe–4S] cluster, consistent with its role as a late Fe–S carrier (Hum Mol Genet, Aug 2020, https://doi.org/10.1093/hmg/ddaa172; IUBMB Life, Jan 2022, https://doi.org/10.1002/iub.2597) (jain2020assemblyofthe pages 3-4, maio2022mammalianironsulfur pages 7-9).
- Molecular function in Fe–S biogenesis. NFU1 receives two [2Fe–2S] units from upstream donors and (with reducing equivalents) assembles a [4Fe–4S] center that it delivers to specific mitochondrial client proteins. Mechanistic mapping identifies a conserved hydrophobic patch at the end of the NFU1 C‑terminal α-helix essential for interactions with donors (ISCU2/ISCA1) and for cluster acquisition (Hum Mol Genet, Aug 2020, https://doi.org/10.1093/hmg/ddaa172) (jain2020assemblyofthe pages 2-2, jain2020assemblyofthe pages 16-17, jain2020assemblyofthe pages 19-20).
- Pathway positioning. Core mitochondrial Fe–S assembly begins on ISCU (primary scaffold), with HSC20–HSPA9 chaperone-cochaperone mediating release. Secondary carriers/converters (GLRX5, ISCA1/2, IBA57, BOLA3) form nodes that assemble and route [4Fe–4S] clusters to clients; NFU1 functions as a late carrier in this network (IUBMB Life, Jan 2022, https://doi.org/10.1002/iub.2597; Hum Mol Genet, Aug 2020, https://doi.org/10.1093/hmg/ddaa172) (maio2022mammalianironsulfur pages 7-9, jain2020assemblyofthe pages 3-4).

2) Recent developments and latest research (prioritize 2023–2024)
- Mitoribosome Fe–S clusters and METTL17. A 2023 study showed that human mitoribosomes contain three structural [2Fe–2S] clusters supplied by a GLRX5–BOLA3 node, and proposed that the mtSSU assembly factor METTL17 (with a [4Fe–4S] cluster) receives its cluster via an ISCA1–NFU1 node. Fibroblasts from NFU1 or BOLA3 patients exhibit attenuated mitochondrial protein synthesis, linking NFU1 dysfunction to translation defects in addition to canonical client maturation (Nucleic Acids Research, Oct 2023, https://doi.org/10.1093/nar/gkad842) (zhong2023bola3andnfu1 pages 1-2).
- System-level pathway mapping. Earlier mechanistic work consolidated in 2020–2022 reviews supports multiple, partially overlapping routes for [4Fe–4S] assembly/delivery to NFU1, with ISCU2→ISCA1→NFU1 as a predominant in vivo route and GLRX5–BOLA3 as an alternative or parallel node depending on client specificity (Hum Mol Genet, Aug 2020, https://doi.org/10.1093/hmg/ddaa172; IUBMB Life, Jan 2022, https://doi.org/10.1002/iub.2597) (jain2020assemblyofthe pages 3-4, maio2022mammalianironsulfur pages 7-9).

3) Current applications and real-world implementations
- Clinical genetics and diagnosis. Biallelic NFU1 variants cause Multiple Mitochondrial Dysfunction Syndrome type 1 (MMDS1) characterized by early-onset leukoencephalopathy, lactic acidosis, nonketotic hyperglycinemia, and frequent pulmonary hypertension. Diagnostic work-ups leverage elevated lactate, pyruvate, and glycine, plus targeted/exome sequencing of Fe–S pathway genes (Biomedicines, Aug 2021, https://doi.org/10.3390/biomedicines9080989) (lebigot2021areviewof pages 20-21).
- Functional assays in patient cells. Complementation with wild-type NFU1 restores lipoylation and client stability; pathogenic variants fail to rescue lipoylation (PDH, OGDH) and SDHB levels, supporting variant interpretation in clinical diagnostics (Hum Mol Genet, Aug 2020, https://doi.org/10.1093/hmg/ddaa172) (jain2020assemblyofthe pages 15-16).

4) Expert opinions and analyses from authoritative sources
- Fe–S pathway positioning and disease mapping. Authoritative reviews emphasize NFU1 as a late Fe–S carrier operating with ISCA1/2, IBA57, BOLA3, and GLRX5; mutations in these factors define MMDS subtypes. Commentaries highlight the association of NFU1 dysfunction with pulmonary arterial hypertension, expanding the recognized clinical spectrum (IUBMB Life, Jan 2022, https://doi.org/10.1002/iub.2597) (maio2022mammalianironsulfur pages 7-9).
- Mechanistic consolidation. Genetic, biochemical, and interaction studies support a model where NFU1 dimerizes to ligate a bridging [4Fe–4S] cluster formed by coordinated donations from ISCU2 and ISCA1, aided by FDX2; NFU1 primarily serves LIAS and, to a degree, SDHB/complex II and selected [4Fe–4S] clients (Hum Mol Genet, Aug 2020, https://doi.org/10.1093/hmg/ddaa172; eLife, Aug 2016, https://doi.org/10.7554/eLife.15991) (jain2020assemblyofthe pages 14-15, melber2016roleofnfu1 pages 1-2).

5) Relevant statistics and data from recent studies
- Variant-function data. Three NFU1 missense variants (N226D, M227I, Y231C) reduce or alter interactions with ISCA1/ISCU2 and fail to complement NFU1 loss in patient fibroblasts, evidenced by lack of restoration of PDH/OGDH lipoylation and SDHB protein levels (Hum Mol Genet, Aug 2020, https://doi.org/10.1093/hmg/ddaa172) (jain2020assemblyofthe pages 15-16).
- Transcriptional compensation. NFU1-deficient patient cells upregulate ISCU and ISCA1 mRNAs under both normoxia and 2.5% O2, indicating compensatory responses within the Fe–S network (Hum Mol Genet, Aug 2020, https://doi.org/10.1093/hmg/ddaa172) (jain2020assemblyofthe pages 14-15).
- Mitochondrial translation attenuation. Patient fibroblasts with NFU1 or BOLA3 mutations show decreased mitochondrial protein synthesis, consistent with impaired mitoribosome cluster assembly (Nucleic Acids Research, Oct 2023, https://doi.org/10.1093/nar/gkad842) (zhong2023bola3andnfu1 pages 1-2).

Mechanistic pathway and client specificity
- Upstream donors and assembly on NFU1. ISCU2 (primary scaffold) and ISCA1 (secondary carrier) directly donate [2Fe–2S] clusters to NFU1; FDX2 provides electrons for reductive coupling into a [4Fe–4S] on the NFU1 dimer. Mutations at NFU1’s conserved FY/hydrophobic region abolish acquisition and delivery to clients (Hum Mol Genet, Aug 2020, https://doi.org/10.1093/hmg/ddaa172) (jain2020assemblyofthe pages 16-17, jain2020assemblyofthe pages 19-20, jain2020assemblyofthe pages 2-2).
- Alternative nodes and client routing. The GLRX5–BOLA3 node can supply [4Fe–4S] to certain clients or to NFU1 in vitro; ISCA1/2 with IBA57 assemble [4Fe–4S] for a subset of targets; HSC20–HSPA9 mediate ISCU2 release and delivery to LYR-motif clients (e.g., SDHB). Distinct phenotypes of GLRX5 versus NFU1 deficiency suggest partial pathway overlap but different physiological priorities (Hum Mol Genet, Aug 2020, https://doi.org/10.1093/hmg/ddaa172; eLife, Aug 2016, https://doi.org/10.7554/eLife.15991) (jain2020assemblyofthe pages 3-4, jain2020assemblyofthe pages 17-18, melber2016roleofnfu1 pages 1-2).
- Primary clients and consequences. LIAS is a principal NFU1 client; NFU1 loss impairs lipoylation of PDH, OGDH, and the glycine cleavage system, explaining lactic acidosis and hyperglycinemia in MMDS1. Effects on SDHB/complex II vary with context; ISCA1 loss causes pronounced SDHB decrease whereas NFU1 patient cells show milder SDHB reduction, indicating client-specific routing (Hum Mol Genet, Aug 2020, https://doi.org/10.1093/hmg/ddaa172; eLife, Aug 2016, https://doi.org/10.7554/eLife.15991) (jain2020assemblyofthe pages 14-15, melber2016roleofnfu1 pages 1-2).

Disease associations and phenotypes
- MMDS1 and clinical spectrum. Biallelic NFU1 variants cause MMDS1 with early-onset leukoencephalopathy, lactic acidosis, nonketotic hyperglycinemia, and frequent pulmonary hypertension; phenotypes extend to autosomal recessive spastic paraplegia in some cases. Foundational genetic studies first linked NFU1 and BOLA3 to combined respiratory chain deficiency and 2-oxoacid dehydrogenase defects with impaired lipoylation (Am J Hum Genet, Oct–Nov 2011, https://doi.org/10.1016/j.ajhg.2011.08.011; https://doi.org/10.1016/j.ajhg.2011.10.005). Later synthesis confirms these associations and diagnostic features (Biomedicines, Aug 2021, https://doi.org/10.3390/biomedicines9080989; IUBMB Life, Jan 2022, https://doi.org/10.1002/iub.2597) (maio2022mammalianironsulfur pages 7-9, lebigot2021areviewof pages 20-21, melber2016roleofnfu1 pages 1-2).
- Translational defect linkage (2023). NFU1 dysfunction is newly linked to impaired mitoribosome function via METTL17 and mitoribosomal Fe–S clusters, providing an additional pathophysiological axis for MMDS1 (Nucleic Acids Research, Oct 2023, https://doi.org/10.1093/nar/gkad842) (zhong2023bola3andnfu1 pages 1-2).

Expert synthesis and open questions
- Converging evidence positions NFU1 as a selective, late [4Fe–4S] carrier with strongest, direct support for servicing LIAS, thereby controlling mitochondrial protein lipoylation. Distinct routing via ISCA1 and GLRX5–BOLA3 likely underlies client selectivity (e.g., SDHB) and phenotypic variability. Open questions include the full hierarchy between ISCA1/2–IBA57 versus GLRX5–BOLA3 routes in different tissues and stress conditions, and how redox-sensitive Fe–S elements in the mitoribosome and METTL17 integrate into metabolic signaling (Hum Mol Genet, Aug 2020; Nucleic Acids Research, Oct 2023; IUBMB Life, Jan 2022) (jain2020assemblyofthe pages 3-4, zhong2023bola3andnfu1 pages 1-2, maio2022mammalianironsulfur pages 7-9).

Embedded summary table
| Topic | Key points | Representative sources with year and DOI/URL |
|---|---|---|
| Identity / Localization / Family | NFU1 is a mitochondrial (matrix) NifU/NFU-family protein with a conserved C‑terminal Nfu domain and a degenerate N‑terminal module; mammalian NFU1 is encoded by NFU1 (UniProt Q9UMS0). | Jain et al., 2020, DOI: 10.1093/hmg/ddaa172 (jain2020assemblyofthe pages 3-4); Maio & Rouault, 2022, DOI: 10.1002/iub.2597 (maio2022mammalianironsulfur pages 7-9) |
| Molecular function | Acts as a late‑acting [4Fe‑4S] cluster carrier: NFU1 dimerizes and ligates a bridging [4Fe‑4S] cluster that is transferred to specific mitochondrial client proteins. | Jain et al., 2020, DOI: 10.1093/hmg/ddaa172 (jain2020assemblyofthe pages 3-4), Melber et al., 2016, DOI: 10.7554/eLife.15991 (melber2016roleofnfu1 pages 1-2) |
| Upstream donors / assembly pathway | NFU1 acquires two [2Fe‑2S] units donated by ISCU2 and ISCA1, which are reductively coupled (FDX2 provides electrons) to form the [4Fe‑4S] on NFU1; an alternative GLRX5–BOLA3 route can supply [4Fe‑4S] in vitro. | Jain et al., 2020, DOI: 10.1093/hmg/ddaa172 (jain2020assemblyofthe pages 14-15), Melber et al., 2016 (melber2016roleofnfu1 pages 1-2) |
| Primary clients / biochemical role | Primary client is lipoyl synthase (LIAS) — NFU1 supplies the auxiliary Fe‑S cluster required for LIAS activity and thus for lipoylation of PDH, OGDH/KGDH and the glycine cleavage system; NFU1 perturbation also affects SDHB/complex II levels variably. | Jain et al., 2020, DOI: 10.1093/hmg/ddaa172 (jain2020assemblyofthe pages 14-15), Melber et al., 2016 (melber2016roleofnfu1 pages 1-2) |
| Interaction network | Functions downstream of ISCU and the HSC20–HSPA9 cochaperone system and cooperates with ISCA1/ISCA2, IBA57, BOLA3 and GLRX5 in late mitochondrial Fe‑S maturation and delivery. | Maio & Rouault, 2022, DOI: 10.1002/iub.2597 (maio2022mammalianironsulfur pages 7-9); Jain et al., 2020 (jain2020assemblyofthe pages 3-4) |
| 2023–2024 update | NFU1 (ISCA1–NFU1 node) implicated in assembly/delivery of Fe‑S clusters required for METTL17 (a mitoribosome biogenesis factor with a [4Fe‑4S] cluster); GLRX5–BOLA3 supplies mitoribosome [2Fe‑2S] clusters; NFU1/BOLA3 deficiency attenuates mitochondrial translation. | Zhong et al., 2023, NAR, DOI: 10.1093/nar/gkad842 (zhong2023bola3andnfu1 pages 1-2) |
| Disease associations & phenotypes | Biallelic NFU1 mutations cause MMDS1 (Multiple Mitochondrial Dysfunction Syndrome type 1) with early‑onset leukoencephalopathy, lactic acidosis, non‑ketotic hyperglycinemia and frequent pulmonary hypertension; linked phenotypes include autosomal recessive spastic paraplegia (SPG93) and translation attenuation in patient fibroblasts. | Clinical/genetic studies summarized in review and experimental reports: Lebigot et al., 2021 (lebigot2021areviewof pages 20-21), Melber et al., 2016 (melber2016roleofnfu1 pages 1-2) |
| Experimental evidence types | Supported by in vitro biochemical cluster‑transfer/reconstitution, structural/interaction mapping, patient genetics (pathogenic variants and genotype–phenotype), complementation in patient fibroblasts, proteomics and enzymatic assays (lipoylation, respiratory complex abundance). | Jain et al., 2020 (jain2020assemblyofthe pages 3-4), Melber et al., 2016 (melber2016roleofnfu1 pages 1-2), Zhong et al., 2023 (zhong2023bola3andnfu1 pages 1-2) |
| Notable pathogenic variants / functional readouts | Specific NFU1 variants (e.g., N226D, M227I, Y231C) impair interactions with ISCA1/ISCU2 and fail to restore lipoylation or SDHB levels in complementation assays, linking molecular defect to biochemical loss (lipoylation, PDH/KGDH) and clinical MMDS1. | Jain et al., 2020, DOI: 10.1093/hmg/ddaa172 (jain2020assemblyofthe pages 15-16) |

Table: Concise table summarizing human NFU1 identity, mechanistic role in mitochondrial Fe–S [4Fe‑4S] delivery, key partners and clients, 2023 update on mitoribosome links, disease associations, and the main experimental evidence with representative citations.

Gene symbol ambiguity and verification
- The symbol NFU1 corresponds to human NFU1 iron–sulfur cluster scaffold homolog, mitochondrial (UniProt Q9UMS0). Literature confirms mitochondrial localization, NifU/Nfu family membership, and late Fe–S carrier function in Homo sapiens; no conflicting gene targets were used in this report (Hum Mol Genet, Aug 2020, https://doi.org/10.1093/hmg/ddaa172; IUBMB Life, Jan 2022, https://doi.org/10.1002/iub.2597) (jain2020assemblyofthe pages 3-4, maio2022mammalianironsulfur pages 7-9).

Cited sources (with dates/URLs)
- Jain et al., Human Molecular Genetics, Aug 2020. https://doi.org/10.1093/hmg/ddaa172 (jain2020assemblyofthe pages 3-4, jain2020assemblyofthe pages 15-16, jain2020assemblyofthe pages 17-18, jain2020assemblyofthe pages 16-17, jain2020assemblyofthe pages 19-20, jain2020assemblyofthe pages 14-15, jain2020assemblyofthe pages 2-2)
- Zhong et al., Nucleic Acids Research, Oct 2023. https://doi.org/10.1093/nar/gkad842 (zhong2023bola3andnfu1 pages 1-2)
- Maio & Rouault, IUBMB Life, Jan 2022. https://doi.org/10.1002/iub.2597 (maio2022mammalianironsulfur pages 7-9)
- Melber et al., eLife, Aug 2016. https://doi.org/10.7554/eLife.15991 (melber2016roleofnfu1 pages 1-2)
- Lebigot et al., Biomedicines, Aug 2021. https://doi.org/10.3390/biomedicines9080989 (lebigot2021areviewof pages 20-21)
- Cameron et al., American Journal of Human Genetics, Oct 2011. https://doi.org/10.1016/j.ajhg.2011.08.011 (melber2016roleofnfu1 pages 1-2)
- Navarro-Sastre et al., American Journal of Human Genetics, Nov 2011. https://doi.org/10.1016/j.ajhg.2011.10.005 (melber2016roleofnfu1 pages 1-2)

References

(jain2020assemblyofthe pages 3-4): Anshika Jain, Anamika Singh, Nunziata Maio, and Tracey A Rouault. Assembly of the [4fe–4s] cluster of nfu1 requires the coordinated donation of two [2fe–2s] clusters from the scaffold proteins, iscu2 and isca1. Human Molecular Genetics, 29:3165-3182, Aug 2020. URL: https://doi.org/10.1093/hmg/ddaa172, doi:10.1093/hmg/ddaa172. This article has 27 citations and is from a domain leading peer-reviewed journal.
(maio2022mammalianironsulfur pages 7-9): Nunziata Maio and Tracey A. Rouault. Mammalian iron sulfur cluster biogenesis and human diseases. IUBMB Life, 74:705-714, Jan 2022. URL: https://doi.org/10.1002/iub.2597, doi:10.1002/iub.2597. This article has 26 citations and is from a peer-reviewed journal.
(jain2020assemblyofthe pages 2-2): Anshika Jain, Anamika Singh, Nunziata Maio, and Tracey A Rouault. Assembly of the [4fe–4s] cluster of nfu1 requires the coordinated donation of two [2fe–2s] clusters from the scaffold proteins, iscu2 and isca1. Human Molecular Genetics, 29:3165-3182, Aug 2020. URL: https://doi.org/10.1093/hmg/ddaa172, doi:10.1093/hmg/ddaa172. This article has 27 citations and is from a domain leading peer-reviewed journal.
(jain2020assemblyofthe pages 16-17): Anshika Jain, Anamika Singh, Nunziata Maio, and Tracey A Rouault. Assembly of the [4fe–4s] cluster of nfu1 requires the coordinated donation of two [2fe–2s] clusters from the scaffold proteins, iscu2 and isca1. Human Molecular Genetics, 29:3165-3182, Aug 2020. URL: https://doi.org/10.1093/hmg/ddaa172, doi:10.1093/hmg/ddaa172. This article has 27 citations and is from a domain leading peer-reviewed journal.
(jain2020assemblyofthe pages 19-20): Anshika Jain, Anamika Singh, Nunziata Maio, and Tracey A Rouault. Assembly of the [4fe–4s] cluster of nfu1 requires the coordinated donation of two [2fe–2s] clusters from the scaffold proteins, iscu2 and isca1. Human Molecular Genetics, 29:3165-3182, Aug 2020. URL: https://doi.org/10.1093/hmg/ddaa172, doi:10.1093/hmg/ddaa172. This article has 27 citations and is from a domain leading peer-reviewed journal.
(zhong2023bola3andnfu1 pages 1-2): Hui Zhong, Alexandre Janer, Oleh Khalimonchuk, Hana Antonicka, Eric A Shoubridge, and Antoni Barrientos. Bola3 and nfu1 link mitoribosome iron–sulfur cluster assembly to multiple mitochondrial dysfunctions syndrome. Nucleic Acids Research, 51:11797-11812, Oct 2023. URL: https://doi.org/10.1093/nar/gkad842, doi:10.1093/nar/gkad842. This article has 31 citations and is from a highest quality peer-reviewed journal.
(lebigot2021areviewof pages 20-21): Elise Lebigot, Manuel Schiff, and Marie-Pierre Golinelli-Cohen. A review of multiple mitochondrial dysfunction syndromes, syndromes associated with defective fe-s protein maturation. Biomedicines, 9:989, Aug 2021. URL: https://doi.org/10.3390/biomedicines9080989, doi:10.3390/biomedicines9080989. This article has 28 citations and is from a poor quality or predatory journal.
(jain2020assemblyofthe pages 15-16): Anshika Jain, Anamika Singh, Nunziata Maio, and Tracey A Rouault. Assembly of the [4fe–4s] cluster of nfu1 requires the coordinated donation of two [2fe–2s] clusters from the scaffold proteins, iscu2 and isca1. Human Molecular Genetics, 29:3165-3182, Aug 2020. URL: https://doi.org/10.1093/hmg/ddaa172, doi:10.1093/hmg/ddaa172. This article has 27 citations and is from a domain leading peer-reviewed journal.
(jain2020assemblyofthe pages 14-15): Anshika Jain, Anamika Singh, Nunziata Maio, and Tracey A Rouault. Assembly of the [4fe–4s] cluster of nfu1 requires the coordinated donation of two [2fe–2s] clusters from the scaffold proteins, iscu2 and isca1. Human Molecular Genetics, 29:3165-3182, Aug 2020. URL: https://doi.org/10.1093/hmg/ddaa172, doi:10.1093/hmg/ddaa172. This article has 27 citations and is from a domain leading peer-reviewed journal.
(melber2016roleofnfu1 pages 1-2): Andrew Melber, Un Na, Ajay Vashisht, Benjamin D Weiler, Roland Lill, James A Wohlschlegel, and Dennis R Winge. Role of nfu1 and bol3 in iron-sulfur cluster transfer to mitochondrial clients. eLife, Aug 2016. URL: https://doi.org/10.7554/elife.15991, doi:10.7554/elife.15991. This article has 143 citations and is from a domain leading peer-reviewed journal.
(jain2020assemblyofthe pages 17-18): Anshika Jain, Anamika Singh, Nunziata Maio, and Tracey A Rouault. Assembly of the [4fe–4s] cluster of nfu1 requires the coordinated donation of two [2fe–2s] clusters from the scaffold proteins, iscu2 and isca1. Human Molecular Genetics, 29:3165-3182, Aug 2020. URL: https://doi.org/10.1093/hmg/ddaa172, doi:10.1093/hmg/ddaa172. This article has 27 citations and is from a domain leading peer-reviewed journal.

Citations

lebigot2021areviewof pages 20-21
jain2020assemblyofthe pages 15-16
maio2022mammalianironsulfur pages 7-9
jain2020assemblyofthe pages 14-15
jain2020assemblyofthe pages 3-4
jain2020assemblyofthe pages 2-2
jain2020assemblyofthe pages 16-17
jain2020assemblyofthe pages 19-20
jain2020assemblyofthe pages 17-18
4Fe–4S
2Fe–2S
4Fe‑4S
2Fe‑2S
4fe–4s
2fe–2s
https://doi.org/10.1093/hmg/ddaa172;
https://doi.org/10.1002/iub.2597
https://doi.org/10.1093/hmg/ddaa172
https://doi.org/10.1002/iub.2597;
https://doi.org/10.1093/nar/gkad842
https://doi.org/10.3390/biomedicines9080989
https://doi.org/10.7554/eLife.15991
https://doi.org/10.1016/j.ajhg.2011.08.011;
https://doi.org/10.1016/j.ajhg.2011.10.005
https://doi.org/10.3390/biomedicines9080989;
https://doi.org/10.1016/j.ajhg.2011.08.011
https://doi.org/10.1093/hmg/ddaa172,
https://doi.org/10.1002/iub.2597,
https://doi.org/10.1093/nar/gkad842,
https://doi.org/10.3390/biomedicines9080989,
https://doi.org/10.7554/elife.15991,

📄 View Raw YAML

id: Q9UMS0
gene_symbol: NFU1
product_type: PROTEIN
status: COMPLETE
taxon:
  id: NCBITaxon:9606
  label: Homo sapiens
description: NFU1 encodes a mitochondrial matrix protein of the NifU/NFU family 
  that functions as a late-acting [4Fe-4S] cluster carrier in mitochondrial 
  iron-sulfur cluster biogenesis. The protein dimerizes and ligates a bridging 
  [4Fe-4S] cluster that is transferred to specific client proteins. NFU1 
  receives two [2Fe-2S] units from upstream donors ISCU2 and ISCA1, which are 
  reductively coupled (with electrons from FDX2) to form the [4Fe-4S] cluster. 
  The primary client is lipoyl synthase (LIAS), which requires the auxiliary 
  [4Fe-4S] cluster for its catalytic activity. NFU1 dysfunction therefore 
  impairs lipoylation of pyruvate dehydrogenase (PDH), 2-oxoglutarate 
  dehydrogenase (OGDH), and the glycine cleavage system, explaining the 
  metabolic features of NFU1 deficiency. Biallelic mutations in NFU1 cause 
  Multiple Mitochondrial Dysfunctions Syndrome type 1 (MMDS1), characterized by 
  early-onset leukoencephalopathy, lactic acidosis, nonketotic hyperglycinemia, 
  and pulmonary hypertension. Alternative splicing produces isoforms with 
  distinct subcellular localizations, with isoform I targeted to mitochondria 
  and isoform II present in cytosol and nucleus.
existing_annotations:
  - term:
      id: GO:0005739
      label: mitochondrion
    evidence_type: IBA
    original_reference_id: GO_REF:0000033
    review:
      summary: NFU1 is established as a mitochondrial protein through multiple 
        lines of evidence. The IBA annotation from phylogenetic analysis is 
        well-supported by direct experimental evidence showing mitochondrial 
        localization of isoform I (PMID:12886008), mitochondrial matrix 
        localization from Reactome pathway analysis, and high-confidence 
        mitochondrial proteomics (PMID:34800366).
      action: ACCEPT
      reason: Mitochondrial localization is a core feature of NFU1 function. The
        protein functions specifically in mitochondrial Fe-S cluster biogenesis 
        and is targeted to the mitochondrial matrix (PMID:12886008, 
        Reactome:R-HSA-6793591). This is the primary site of NFU1 function.
      supported_by:
        - reference_id: PMID:12886008
          supporting_text: Isoform I is localized in the mitochondria, whereas 
            isoform II is present in the cytosol and the nucleus.
        - reference_id: file:human/NFU1/NFU1-deep-research-falcon.md
          supporting_text: 'model: Edison Scientific Literature'
  - term:
      id: GO:0051604
      label: protein maturation
    evidence_type: IBA
    original_reference_id: GO_REF:0000033
    review:
      summary: NFU1 participates in the maturation of [4Fe-4S] 
        cluster-containing proteins by delivering Fe-S clusters to target 
        proteins. The IBA annotation reflects the conserved role of NFU family 
        proteins in Fe-S protein maturation across species.
      action: MODIFY
      reason: While NFU1 does participate in protein maturation, the term 
        "protein maturation" (GO:0051604) is too general. The specific role of 
        NFU1 is in iron-sulfur cluster assembly and delivery to target proteins.
        The more specific process term GO:0016226 (iron-sulfur cluster assembly)
        better captures NFU1's function (PMID:12886008, PMID:28906594).
      proposed_replacement_terms:
        - id: GO:0016226
          label: iron-sulfur cluster assembly
  - term:
      id: GO:0051539
      label: 4 iron, 4 sulfur cluster binding
    evidence_type: IBA
    original_reference_id: GO_REF:0000033
    review:
      summary: The IBA annotation for [4Fe-4S] cluster binding is strongly 
        supported by direct biochemical evidence. Tong et al. (2003) 
        demonstrated using UV-visible absorption and 57Fe Mossbauer spectroscopy
        that purified human Nfu assembles approximately one labile [4Fe-4S] 
        cluster per two monomers (PMID:12886008). Wesley et al. (2017) further 
        characterized [4Fe-4S] cluster binding and its disruption by 
        disease-causing mutations (PMID:28906594).
      action: ACCEPT
      reason: '[4Fe-4S] cluster binding is the core molecular function of NFU1. The
        protein dimerizes and ligates a bridging [4Fe-4S] cluster that is subsequently
        delivered to target proteins. This has been demonstrated by multiple spectroscopic
        and biochemical studies.'
      supported_by:
        - reference_id: PMID:12886008
          supporting_text: The results suggest that Nfu can assemble 
            approximately one labile [4Fe-4S] cluster per two Nfu monomers, and 
            support the proposal that Nfu is an alternative scaffold protein for
            assembly of clusters that are subsequently used for maturation of 
            targeted Fe-S proteins.
        - reference_id: PMID:28906594
          supporting_text: iron-sulfur (Fe/S) cluster-containing proteins 
            constitute one of the largest protein classes, with highly varied 
            function...we have characterized the impact of defects occurring in 
            the MMDS1 disease state that result from a point mutation 
            (p.Gly189Arg) near the active site of NFU1, an Fe/S scaffold 
            protein.
  - term:
      id: GO:0005506
      label: iron ion binding
    evidence_type: IEA
    original_reference_id: GO_REF:0000002
    review:
      summary: The IEA annotation for iron ion binding is derived from InterPro 
        domain mapping (IPR001075). Direct experimental evidence supports iron 
        binding as part of the [4Fe-4S] cluster (PMID:12886008).
      action: ACCEPT
      reason: Iron ion binding is inherent to NFU1's function as an Fe-S cluster
        scaffold. The [4Fe-4S] cluster contains four iron atoms that are 
        coordinated by the protein. While this is a more general term than 
        [4Fe-4S] cluster binding, it is not incorrect and provides complementary
        information about metal binding capacity.
      supported_by:
        - reference_id: PMID:12886008
          supporting_text: Nfu can assemble approximately one labile [4Fe-4S] 
            cluster per two Nfu monomers
  - term:
      id: GO:0005739
      label: mitochondrion
    evidence_type: IEA
    original_reference_id: GO_REF:0000044
    review:
      summary: The IEA annotation from UniProtKB subcellular location mapping is
        consistent with direct experimental evidence. Multiple IDA annotations 
        also support mitochondrial localization.
      action: ACCEPT
      reason: While this duplicates the IBA annotation, the evidence source 
        (UniProt subcellular location mapping) provides independent support. 
        Mitochondrial localization is well-established.
  - term:
      id: GO:0005829
      label: cytosol
    evidence_type: IEA
    original_reference_id: GO_REF:0000044
    review:
      summary: Cytosolic localization has experimental support from Tong et al. 
        (2003) who showed that alternative splicing produces isoforms with 
        distinct localizations - isoform II lacks the mitochondrial targeting 
        sequence and localizes to cytosol and nucleus (PMID:12886008).
      action: KEEP_AS_NON_CORE
      reason: While cytosolic localization is experimentally validated for 
        isoform II, the primary function of NFU1 in iron-sulfur cluster 
        biogenesis occurs in mitochondria. The cytosolic isoform represents an 
        alternative localization that may have secondary functions.
      supported_by:
        - reference_id: PMID:12886008
          supporting_text: Isoform I is localized in the mitochondria, whereas 
            isoform II is present in the cytosol and the nucleus.
  - term:
      id: GO:0016226
      label: iron-sulfur cluster assembly
    evidence_type: IEA
    original_reference_id: GO_REF:0000002
    review:
      summary: The IEA annotation from InterPro (IPR001075) correctly identifies
        NFU1's role in iron-sulfur cluster assembly. This is strongly supported 
        by direct experimental evidence (PMID:12886008, PMID:28906594).
      action: ACCEPT
      reason: Iron-sulfur cluster assembly is the primary biological process in 
        which NFU1 participates. NFU1 functions as a late-acting 
        scaffold/carrier that assembles [4Fe-4S] clusters and delivers them to 
        target proteins including LIAS.
      supported_by:
        - reference_id: PMID:12886008
          supporting_text: Nfu is an alternative scaffold protein for assembly 
            of clusters that are subsequently used for maturation of targeted 
            Fe-S proteins.
  - term:
      id: GO:0046872
      label: metal ion binding
    evidence_type: IEA
    original_reference_id: GO_REF:0000043
    review:
      summary: The IEA annotation from UniProt keyword mapping is very general. 
        NFU1 binds iron as part of iron-sulfur clusters.
      action: MARK_AS_OVER_ANNOTATED
      reason: While technically correct (NFU1 binds iron ions as part of the 
        [4Fe-4S] cluster), this term is too general and uninformative. The more 
        specific terms GO:0051539 (4 iron, 4 sulfur cluster binding) and 
        GO:0005506 (iron ion binding) already capture this information with 
        greater specificity.
  - term:
      id: GO:0051536
      label: iron-sulfur cluster binding
    evidence_type: IEA
    original_reference_id: GO_REF:0000120
    review:
      summary: The IEA annotation for general iron-sulfur cluster binding is 
        correct but less specific than the [4Fe-4S] cluster binding term that is
        also annotated.
      action: ACCEPT
      reason: This general term is acceptable as NFU1 can bind both [2Fe-2S] and
        [4Fe-4S] clusters during its function (PMID:27538573 shows [2Fe-2S] 
        binding; PMID:12886008 shows [4Fe-4S]). The more general term captures 
        this broader capacity.
      supported_by:
        - reference_id: PMID:27538573
          supporting_text: Human holo Nfu shows a dimer-tetramer equilibrium 
            with a protein to cluster ratio of 2:1, reflecting the Nfu-bridging 
            [2Fe-2S] cluster.
  - term:
      id: GO:0005515
      label: protein binding
    evidence_type: IPI
    original_reference_id: PMID:22190034
    review:
      summary: This annotation is from a large-scale HIV-human interactome 
        study. The biological relevance of interactions detected in such studies
        for normal NFU1 function is unclear.
      action: MARK_AS_OVER_ANNOTATED
      reason: The term "protein binding" is uninformative and does not capture 
        the specific functional interactions of NFU1 with Fe-S biogenesis 
        partners (BOLA3, HSPA9, ISCU, ISCA1). Large-scale interactome studies 
        often detect interactions that may not be physiologically relevant.
      supported_by:
        - reference_id: PMID:22190034
          supporting_text: Global landscape of HIV-human protein complexes.
  - term:
      id: GO:0005515
      label: protein binding
    evidence_type: IPI
    original_reference_id: PMID:25416956
    review:
      summary: This annotation is from a proteome-scale human interactome map. 
        While demonstrating NFU1 interacts with other proteins, "protein 
        binding" is uninformative.
      action: MARK_AS_OVER_ANNOTATED
      reason: The generic "protein binding" term does not capture the 
        biologically meaningful interactions of NFU1. More informative 
        annotations would specify interactions with Fe-S cluster biogenesis 
        components.
      supported_by:
        - reference_id: PMID:25416956
          supporting_text: A proteome-scale map of the human interactome 
            network.
  - term:
      id: GO:0005515
      label: protein binding
    evidence_type: IPI
    original_reference_id: PMID:27532772
    review:
      summary: This reference (Uzarska et al. 2016, eLife) demonstrates specific
        interaction between NFU1 and BOLA3 as part of Fe-S cluster biogenesis. 
        This is a biologically meaningful interaction showing BOLA3 
        preferentially interacts with holo-NFU1.
      action: MODIFY
      reason: While the IPI evidence for protein binding is valid, a more 
        informative term could capture the specific functional role. However, 
        without a specific GO term for "BOLA3 binding" or similar, this 
        annotation provides evidence of a physiologically relevant interaction 
        in Fe-S cluster transfer.
      proposed_replacement_terms:
        - id: GO:0140132
          label: iron-sulfur cluster chaperone activity
      additional_reference_ids:
        - PMID:27532772
      supported_by:
        - reference_id: PMID:27532772
          supporting_text: Preferential interaction of BOLA1 with holo-GLRX5 and
            of BOLA3 with holo-NFU1
  - term:
      id: GO:0005515
      label: protein binding
    evidence_type: IPI
    original_reference_id: PMID:32296183
    review:
      summary: This annotation is from a reference map of the human binary 
        protein interactome (HuRI). While detecting interactions, the generic 
        term is uninformative for understanding NFU1 function.
      action: MARK_AS_OVER_ANNOTATED
      reason: Large-scale interactome data, while valuable for network analysis,
        produces generic "protein binding" annotations that do not illuminate 
        NFU1's specific role in Fe-S cluster biogenesis.
      supported_by:
        - reference_id: PMID:32296183
          supporting_text: Apr 8. A reference map of the human binary protein 
            interactome.
  - term:
      id: GO:0005829
      label: cytosol
    evidence_type: IDA
    original_reference_id: GO_REF:0000052
    review:
      summary: The IDA from immunofluorescence curation (HPA) detects cytosolic 
        signal. This is consistent with the existence of cytosolic isoform II.
      action: KEEP_AS_NON_CORE
      reason: Cytosolic localization is validated but represents a secondary 
        localization. The primary Fe-S cluster assembly function occurs in 
        mitochondria.
  - term:
      id: GO:0005739
      label: mitochondrion
    evidence_type: HTP
    original_reference_id: PMID:34800366
    review:
      summary: High-throughput mitochondrial proteomics study confirming NFU1 as
        a mitochondrial protein. This provides independent high-confidence 
        support for mitochondrial localization.
      action: ACCEPT
      reason: The quantitative high-confidence human mitochondrial proteome 
        provides strong support for mitochondrial localization of NFU1.
      supported_by:
        - reference_id: PMID:34800366
          supporting_text: Epub 2021 Nov 19. Quantitative high-confidence human 
            mitochondrial proteome and its dynamics in cellular context.
  - term:
      id: GO:0051537
      label: 2 iron, 2 sulfur cluster binding
    evidence_type: IDA
    original_reference_id: PMID:27538573
    review:
      summary: Wachnowsky et al. (2016) demonstrated that human NFU1 can bind a 
        [2Fe-2S] cluster as an intermediate during cluster transfer. The study 
        characterized cluster exchange chemistry and showed NFU1 can accept 
        [2Fe-2S] clusters and transfer them to ferredoxins.
      action: ACCEPT
      reason: The [2Fe-2S] cluster binding capacity is experimentally 
        demonstrated and represents an intermediate state in the cluster 
        maturation pathway. NFU1 receives [2Fe-2S] units from donors that are 
        subsequently converted to [4Fe-4S] clusters.
      supported_by:
        - reference_id: PMID:27538573
          supporting_text: Herein, we characterize the cluster exchange 
            chemistry of human Nfu and its capacity to bind and transfer a 
            [2Fe-2S] cluster
  - term:
      id: GO:0051604
      label: protein maturation
    evidence_type: IDA
    original_reference_id: PMID:27538573
    review:
      summary: The IDA annotation for protein maturation from this reference 
        reflects NFU1's role in maturing Fe-S proteins by delivering clusters. 
        However, the term is generic.
      action: MODIFY
      reason: While NFU1 does contribute to protein maturation, the specific 
        process is iron-sulfur cluster assembly and delivery. The term 
        GO:0016226 (iron-sulfur cluster assembly) more precisely captures NFU1's
        role.
      proposed_replacement_terms:
        - id: GO:0016226
          label: iron-sulfur cluster assembly
      supported_by:
        - reference_id: PMID:27538573
          supporting_text: Epub 2016 Aug 18. Iron-sulfur cluster exchange 
            reactions mediated by the human Nfu protein.
  - term:
      id: GO:0005515
      label: protein binding
    evidence_type: IPI
    original_reference_id: PMID:26702583
    review:
      summary: Shan & Cortopassi (2016) demonstrated that HSPA9/Mortalin 
        interacts with NFU1 as part of the mitochondrial Fe-S cluster biogenesis
        machinery. This is a functionally relevant interaction.
      action: MODIFY
      reason: While "protein binding" is too generic, this reference documents a
        biologically meaningful interaction. HSPA9 is the mitochondrial 
        chaperone that works with the co-chaperone HSC20 in Fe-S cluster 
        transfer. A more specific molecular function term capturing scaffold 
        activity would be more informative.
      proposed_replacement_terms:
        - id: GO:0140132
          label: iron-sulfur cluster chaperone activity
      supported_by:
        - reference_id: PMID:26702583
          supporting_text: HSPA9 interacts with and stabilizes the mitochondrial
            ISC biogenesis proteins frataxin, Nfs1, ISCU, and Nfu.
  - term:
      id: GO:0016226
      label: iron-sulfur cluster assembly
    evidence_type: IDA
    original_reference_id: PMID:28906594
    review:
      summary: Wesley et al. (2017) characterized NFU1's role in Fe-S cluster 
        assembly and how the disease-causing G189R mutation impairs this 
        function. The study directly demonstrates NFU1's function as an Fe-S 
        scaffold protein.
      action: ACCEPT
      reason: This is strong direct experimental evidence for NFU1's role in 
        iron-sulfur cluster assembly. The paper shows that pathogenic mutations 
        impair NFU1's ability to receive and transfer Fe-S clusters.
      supported_by:
        - reference_id: PMID:28906594
          supporting_text: substitution at position 189 triggers structural 
            changes that increase flexibility, decrease stability, and alter the
            monomer-dimer equilibrium toward monomer, thereby impairing the 
            ability of the Gly189X derivatives to receive an Fe/S cluster from 
            physiologically relevant sources.
  - term:
      id: GO:0051539
      label: 4 iron, 4 sulfur cluster binding
    evidence_type: IDA
    original_reference_id: PMID:28906594
    review:
      summary: Direct experimental evidence from MMDS1 disease characterization 
        confirms [4Fe-4S] cluster binding by NFU1. The pathogenic G189R variant 
        disrupts this capacity.
      action: ACCEPT
      reason: This provides disease-relevant experimental validation of [4Fe-4S]
        cluster binding as a core function of NFU1.
      supported_by:
        - reference_id: PMID:28906594
          supporting_text: we have characterized the impact of defects occurring
            in the MMDS1 disease state that result from a point mutation 
            (p.Gly189Arg) near the active site of NFU1, an Fe/S scaffold 
            protein.
  - term:
      id: GO:0005759
      label: mitochondrial matrix
    evidence_type: TAS
    original_reference_id: Reactome:R-HSA-6793591
    review:
      summary: The Reactome pathway for protein lipoylation places NFU1 in the 
        mitochondrial matrix, where it functions to deliver [4Fe-4S] clusters to
        LIAS for lipoyl-GCSH synthesis.
      action: ACCEPT
      reason: Mitochondrial matrix localization is more specific than general 
        mitochondrion annotation and reflects the actual site of NFU1 function 
        in Fe-S cluster delivery to LIAS and other matrix clients.
  - term:
      id: GO:0005829
      label: cytosol
    evidence_type: IDA
    original_reference_id: PMID:12915448
    review:
      summary: Ganesh et al. (2003) identified NFU1 (as HIRIP5) as a cytosolic 
        protein that interacts with laforin. This reflects the cytosolic 
        isoform.
      action: KEEP_AS_NON_CORE
      reason: This provides additional experimental evidence for cytosolic 
        localization of one NFU1 isoform. However, the mitochondrial isoform is 
        the primary functional form for Fe-S cluster biogenesis.
      supported_by:
        - reference_id: PMID:12915448
          supporting_text: HIRIP5 encodes a cytosolic protein and is expressed 
            ubiquitously, perhaps reflecting a house-keeping function.
  - term:
      id: GO:0005506
      label: iron ion binding
    evidence_type: IDA
    original_reference_id: PMID:12886008
    review:
      summary: Tong et al. (2003) directly demonstrated iron binding through 
        spectroscopic analysis of purified NFU1 with assembled Fe-S clusters.
      action: ACCEPT
      reason: Direct experimental evidence from Mossbauer spectroscopy and 
        UV-visible absorption confirms iron binding as part of [4Fe-4S] cluster 
        assembly.
      supported_by:
        - reference_id: PMID:12886008
          supporting_text: "A combination of biochemical and spectroscopic techniques,
            including UV-visible absorption and 57Fe Mössbauer spectroscopies, have
            been used to investigate the ability of purified human Nfu to assemble
            Fe-S clusters"
  - term:
      id: GO:0005634
      label: nucleus
    evidence_type: IDA
    original_reference_id: PMID:12886008
    review:
      summary: Tong et al. (2003) showed that isoform II (lacking mitochondrial 
        targeting sequence) localizes to nucleus in addition to cytosol.
      action: KEEP_AS_NON_CORE
      reason: Nuclear localization is documented for isoform II but represents a
        secondary localization. The functional significance of nuclear NFU1 is 
        not well established.
      supported_by:
        - reference_id: PMID:12886008
          supporting_text: Isoform I is localized in the mitochondria, whereas 
            isoform II is present in the cytosol and the nucleus.
  - term:
      id: GO:0005739
      label: mitochondrion
    evidence_type: IDA
    original_reference_id: PMID:12886008
    review:
      summary: Foundational experimental study demonstrating mitochondrial 
        localization of NFU1 isoform I and its ability to assemble [4Fe-4S] 
        clusters.
      action: ACCEPT
      reason: Primary experimental evidence establishing mitochondrial 
        localization of the functional isoform of NFU1.
      supported_by:
        - reference_id: PMID:12886008
          supporting_text: Isoform I is localized in the mitochondria, whereas 
            isoform II is present in the cytosol and the nucleus.
  - term:
      id: GO:0005829
      label: cytosol
    evidence_type: IDA
    original_reference_id: PMID:12886008
    review:
      summary: Tong et al. (2003) demonstrated cytosolic localization of NFU1 
        isoform II.
      action: KEEP_AS_NON_CORE
      reason: Cytosolic localization is documented for isoform II. This 
        represents secondary localization relative to the mitochondrial 
        function.
      supported_by:
        - reference_id: PMID:12886008
          supporting_text: Isoform I is localized in the mitochondria, whereas 
            isoform II is present in the cytosol and the nucleus.
  - term:
      id: GO:0016226
      label: iron-sulfur cluster assembly
    evidence_type: IDA
    original_reference_id: PMID:12886008
    review:
      summary: This is the foundational study establishing NFU1 as an 
        iron-sulfur cluster scaffold protein capable of assembling [4Fe-4S] 
        clusters for delivery to target proteins.
      action: ACCEPT
      reason: Primary experimental evidence defining NFU1's core biological 
        function in Fe-S cluster assembly. This study established the role of 
        human Nfu as an alternative scaffold in the Fe-S biogenesis pathway.
      supported_by:
        - reference_id: PMID:12886008
          supporting_text: support the proposal that Nfu is an alternative 
            scaffold protein for assembly of clusters that are subsequently used
            for maturation of targeted Fe-S proteins.
  - term:
      id: GO:0051539
      label: 4 iron, 4 sulfur cluster binding
    evidence_type: IDA
    original_reference_id: PMID:12886008
    review:
      summary: The foundational demonstration that NFU1 binds [4Fe-4S] clusters 
        using Mossbauer spectroscopy and biochemical analysis.
      action: ACCEPT
      reason: This provides the primary experimental evidence for [4Fe-4S] 
        cluster binding, which is the core molecular function of NFU1.
      supported_by:
        - reference_id: PMID:12886008
          supporting_text: The results suggest that Nfu can assemble 
            approximately one labile [4Fe-4S] cluster per two Nfu monomers
  - term:
      id: GO:0140132
      label: iron-sulfur cluster chaperone activity
    evidence_type: IDA
    original_reference_id: PMID:12886008
    review:
      summary: NFU1 functions as an iron-sulfur cluster chaperone, assembling 
        [4Fe-4S] clusters and delivering them to target proteins. This molecular
        function term captures the core activity of NFU1 better than "protein 
        binding".
      action: NEW
      reason: This term specifically captures NFU1's role as a late-acting Fe-S 
        cluster chaperone that assembles clusters from [2Fe-2S] intermediates 
        and delivers them to client proteins including LIAS. This is the 
        defining molecular function of NFU1.
      additional_reference_ids:
        - PMID:27538573
        - PMID:28906594
      supported_by:
        - reference_id: PMID:12886008
          supporting_text: support the proposal that Nfu is an alternative 
            scaffold protein for assembly of clusters that are subsequently used
            for maturation of targeted Fe-S proteins.
        - reference_id: PMID:27538573
          supporting_text: Human Nfu is an iron-sulfur cluster protein that has 
            recently been implicated in multiple mitochondrial dysfunctional 
            syndrome
        - reference_id: PMID:28906594
          supporting_text: 'Understanding the molecular basis for multiple mitochondrial
            dysfunctions syndrome 1 (MMDS1): impact of a disease-causing Gly189Arg
            substitution on NFU1.'
references:
  - id: GO_REF:0000002
    title: Gene Ontology annotation through association of InterPro records with
      GO terms
    findings: []
  - id: GO_REF:0000033
    title: Annotation inferences using phylogenetic trees
    findings: []
  - id: GO_REF:0000043
    title: Gene Ontology annotation based on UniProtKB/Swiss-Prot keyword 
      mapping
    findings: []
  - id: GO_REF:0000044
    title: Gene Ontology annotation based on UniProtKB/Swiss-Prot Subcellular 
      Location vocabulary mapping, accompanied by conservative changes to GO 
      terms applied by UniProt
    findings: []
  - id: GO_REF:0000052
    title: Gene Ontology annotation based on curation of immunofluorescence data
    findings: []
  - id: GO_REF:0000120
    title: Combined Automated Annotation using Multiple IEA Methods
    findings: []
  - id: PMID:12886008
    title: Subcellular compartmentalization of human Nfu, an iron-sulfur cluster
      scaffold protein, and its ability to assemble a [4Fe-4S] cluster.
    findings:
      - statement: NFU1 assembles approximately one [4Fe-4S] cluster per two 
          monomers
      - statement: Isoform I localizes to mitochondria; isoform II to cytosol 
          and nucleus
      - statement: Alternative splicing produces isoforms with distinct 
          subcellular localizations
  - id: PMID:12915448
    title: The Lafora disease gene product laforin interacts with HIRIP5, a 
      phylogenetically conserved protein containing a NifU-like domain.
    findings:
      - statement: NFU1 (HIRIP5) identified as cytosolic protein
      - statement: Interacts with laforin through its C-terminal NifU-like 
          domain
  - id: PMID:22190034
    title: Global landscape of HIV-human protein complexes.
    findings: []
  - id: PMID:25416956
    title: A proteome-scale map of the human interactome network.
    findings: []
  - id: PMID:26702583
    title: Mitochondrial Hspa9/Mortalin regulates erythroid differentiation via 
      iron-sulfur cluster assembly.
    findings:
      - statement: HSPA9 interacts with NFU1 as part of mitochondrial ISC 
          biogenesis machinery
      - statement: NFU1 is stabilized by HSPA9 interaction
  - id: PMID:27532772
    title: Mitochondrial Bol1 and Bol3 function as assembly factors for specific
      iron-sulfur proteins.
    findings:
      - statement: BOLA3 preferentially interacts with holo-NFU1
      - statement: NFU1 and BOL proteins have distinct but overlapping functions
          in Fe-S protein maturation
  - id: PMID:27538573
    title: Iron-sulfur cluster exchange reactions mediated by the human Nfu 
      protein.
    findings:
      - statement: NFU1 binds [2Fe-2S] cluster as dimer with 2:1 protein to 
          cluster ratio
      - statement: Cluster can be transferred to apo ferredoxins at relatively 
          fast rates
      - statement: NFU1 implicated in MMDS1
  - id: PMID:28906594
    title: 'Understanding the molecular basis for multiple mitochondrial dysfunctions
      syndrome 1 (MMDS1): impact of a disease-causing Gly189Arg substitution on NFU1.'
    findings:
      - statement: G189R mutation alters protein structure and monomer-dimer 
          equilibrium
      - statement: Disease mutations impair ability to receive Fe-S clusters 
          from donors
  - id: PMID:32296183
    title: A reference map of the human binary protein interactome.
    findings: []
  - id: PMID:34800366
    title: Quantitative high-confidence human mitochondrial proteome and its 
      dynamics in cellular context.
    findings:
      - statement: NFU1 confirmed as high-confidence mitochondrial protein
  - id: Reactome:R-HSA-6793591
    title: LIAS synthesizes lipoyl-GCSH
    findings:
      - statement: NFU1 provides [4Fe-4S] cluster to LIAS in mitochondrial 
          matrix
      - statement: Required for lipoylation pathway
  - id: file:human/NFU1/NFU1-deep-research-falcon.md
    title: Deep research report on NFU1
    findings: []
core_functions:
  - molecular_function:
      id: GO:0140132
      label: iron-sulfur cluster chaperone activity
    description: NFU1 is a late-acting [4Fe-4S] cluster chaperone that receives 
      [2Fe-2S] clusters from upstream donors ISCU2 and ISCA1, assembles them 
      into [4Fe-4S] clusters, and delivers these to target proteins. This 
      chaperone function is demonstrated by biochemical reconstitution, 
      spectroscopic analysis, and functional complementation studies 
      (PMID:12886008, PMID:27538573, PMID:28906594).
    locations:
      - id: GO:0005759
        label: mitochondrial matrix
    directly_involved_in:
      - id: GO:0016226
        label: iron-sulfur cluster assembly
  - molecular_function:
      id: GO:0051539
      label: 4 iron, 4 sulfur cluster binding
    description: NFU1 dimerizes and ligates a bridging [4Fe-4S] cluster. 
      Mossbauer spectroscopy and UV-visible absorption studies demonstrate 
      approximately one [4Fe-4S] cluster per two NFU1 monomers (PMID:12886008). 
      The cluster-binding cysteines (C210 and C213) are essential for function 
      and are disrupted by pathogenic mutations (PMID:28906594).
    locations:
      - id: GO:0005759
        label: mitochondrial matrix
suggested_questions:
  - question: What is the full spectrum of [4Fe-4S] client proteins for NFU1 
      beyond LIAS?
  - question: Does the cytosolic/nuclear isoform II have a distinct function in 
      cytosolic Fe-S cluster biogenesis?
  - question: What determines the specificity of cluster delivery to different 
      client proteins?
  - question: How does the ISCA1-NFU1 pathway differ from the GLRX5-BOLA3 
      pathway in client selectivity?
suggested_experiments:
  - description: Proteomics identification of all NFU1-dependent [4Fe-4S] client
      proteins
  - description: Characterization of cytosolic isoform II function in CIA 
      pathway
  - description: Structure determination of NFU1 in complex with client proteins
  - description: In vivo validation of METTL17 as an NFU1 client for 
      mitoribosome biogenesis
tags:
  - iron-sulfur-cluster-biogenesis

NFU1

Gene Description

Existing Annotations Review

Core Functions

References

Suggested Questions for Experts

Suggested Experiments

Tags

📚 Additional Documentation

Deep Research Falcon

Question

Gene Research for Functional Annotation

⚠️ CRITICAL: Gene/Protein Identification Context

Target Gene/Protein Identity (from UniProt):

MANDATORY VERIFICATION STEPS:

If Gene Symbol is Ambiguous or You Cannot Find Relevant Literature:

Research Target:

Output

Gene Research for Functional Annotation

⚠️ CRITICAL: Gene/Protein Identification Context

Target Gene/Protein Identity (from UniProt):

MANDATORY VERIFICATION STEPS:

If Gene Symbol is Ambiguous or You Cannot Find Relevant Literature:

Research Target:

Citations

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