BOLA3 is a mitochondrial BolA-family protein that functions as a late-acting iron-sulfur (Fe-S) cluster assembly factor. BOLA3 forms a heterocomplex with the mitochondrial monothiol glutaredoxin GLRX5, bridged by a [2Fe-2S] cluster (coordinated by BOLA3 Cys59 and His96, and GLRX5 Cys67 plus glutathione). This GLRX5-BOLA3 complex acts as a [2Fe-2S] carrier/chaperone that delivers cluster equivalents to NFU1, where two [2Fe-2S] clusters are converted to a [4Fe-4S] cluster for insertion into downstream client proteins including lipoyl synthase (LIAS), succinate dehydrogenase, and the mitoribosome. BOLA3 deficiency causes Multiple Mitochondrial Dysfunctions Syndrome type 2 (MMDS2), characterized by defective protein lipoylation, impaired respiratory chain complex activities, and attenuated mitochondrial translation.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0051604 protein maturation | IBA GO_REF:0000033 | MODIFY | Summary: This annotation captures BOLA3's role in facilitating Fe-S cluster insertion into mitochondrial proteins, which is a form of protein maturation. BOLA3 functions in the late ISC pathway to enable [4Fe-4S] protein maturation (PMID:27532772). Reason: While "protein maturation" is technically accurate, it is too general. BOLA3 specifically functions in iron-sulfur cluster assembly and insertion. More precise terms exist that better describe the molecular function. Proposed replacements: iron-sulfur cluster assembly [4Fe-4S] cluster assembly Supporting Evidence: PMID:27532772 Bol1 and Bol3 as specific mitochondrial ISC assembly factors that facilitate [4Fe-4S] cluster insertion into a subset of mitochondrial proteins such as lipoate synthase and succinate dehydrogenase file:human/BOLA3/BOLA3-deep-research-falcon.md model: Edison Scientific Literature |
| GO:0005759 mitochondrial matrix | IBA GO_REF:0000033 | ACCEPT | Summary: BOLA3 localizes to mitochondria where it functions in the mitochondrial ISC assembly pathway. Multiple lines of evidence support mitochondrial localization (PMID:22746225, PMID:27532772). Reason: The mitochondrial matrix localization is well-supported by phylogenetic inference (IBA) and is consistent with experimental data. BOLA3 functions within the mitochondrial ISC pathway alongside GLRX5 and NFU1. Supporting Evidence: PMID:22746225 BOLA1 is a mitochondrial protein PMID:27532772 Mitochondrial Bol1 and Bol3 function as assembly factors for specific iron-sulfur proteins |
| GO:0005739 mitochondrion | IEA GO_REF:0000120 | ACCEPT | Summary: Automated annotation of mitochondrial localization is correct and consistent with experimental data showing BOLA3 is a mitochondrial protein (PMID:22746225). Reason: This IEA annotation is broader than the IBA to mitochondrial matrix but is not incorrect. Multiple annotations at different specificity levels are acceptable. Supporting Evidence: PMID:22746225 We show that BOLA1 is a mitochondrial protein |
| GO:0005515 protein binding | IPI PMID:27499296 Mitochondrial Protein Interaction Mapping Identifies Regulat... | MODIFY | Summary: This annotation captures interaction with GLRX5 from a mitochondrial protein interaction mapping study. The interaction is functionally significant. Reason: "Protein binding" is too vague and uninformative. BOLA3 specifically binds GLRX5 to form a Fe-S cluster-bridged heterocomplex. A more informative MF term should be used. Proposed replacements: 2 iron, 2 sulfur cluster binding Supporting Evidence: PMID:27532772 BOLA1 or BOLA3 and GLRX5 at the atomic level PMID:27499296 2016 Aug 4. Mitochondrial Protein Interaction Mapping Identifies Regulators of Respiratory Chain Function. |
| GO:0005515 protein binding | IPI PMID:27532772 Mitochondrial Bol1 and Bol3 function as assembly factors for... | MODIFY | Summary: This annotation reflects the physical interaction between BOLA3 and GLRX5 demonstrated by NMR spectroscopy. BOLA3 forms a [2Fe-2S]-bridged heterocomplex with GLRX5, with BOLA3 Cys59 and His96 serving as cluster ligands (PMID:27532772). Reason: "Protein binding" does not capture the specific nature of the BOLA3-GLRX5 interaction. The interaction involves forming a Fe-S cluster-bridged complex essential for cluster transfer. Proposed replacements: 2 iron, 2 sulfur cluster binding Supporting Evidence: PMID:27532772 The structures of (A) BOLA1 and (B) BOLA3 were solved by solution NMR. Residues His58, His67 and His102 are conserved within the eukaryotic BOLA1 proteins, and residues Cys59 and His96 are conserved within the BOLA3 proteins |
| GO:0005515 protein binding | IPI PMID:32296183 A reference map of the human binary protein interactome. | MARK AS OVER ANNOTATED | Summary: High-throughput binary interactome mapping study. The specific interaction partners from this study include GLRX5. Reason: Generic "protein binding" from HTP studies provides limited functional insight. The functionally relevant interactions (GLRX5, NFU1) are better captured through more specific annotations. Supporting Evidence: PMID:32296183 Apr 8. A reference map of the human binary protein interactome. |
| GO:0005515 protein binding | IPI PMID:33961781 Dual proteome-scale networks reveal cell-specific remodeling... | MARK AS OVER ANNOTATED | Summary: Dual proteome-scale interactome study. This is a high-throughput study. Reason: Generic "protein binding" from HTP proteome-scale studies is not informative for functional annotation. The core BOLA3-GLRX5 interaction is better captured with more specific terms. Supporting Evidence: PMID:33961781 2021 May 6. Dual proteome-scale networks reveal cell-specific remodeling of the human interactome. |
| GO:0005515 protein binding | IPI PMID:34063696 Molecular Basis of Multiple Mitochondrial Dysfunctions Syndr... | MODIFY | Summary: This study examined the C59Y BOLA3 variant and demonstrated that the mutant still forms a heterocomplex with GLRX5, though with altered properties. The interaction between BOLA3 and GLRX5 involves [2Fe-2S] cluster coordination. Reason: The study provides detailed molecular characterization of the BOLA3-GLRX5 interaction showing cluster binding. More specific terms should be used. Proposed replacements: 2 iron, 2 sulfur cluster binding Supporting Evidence: PMID:34063696 C59Y BOLA3-GLRX5 Complex Bound a [2Fe-2S]2+ Cluster |
| GO:0005739 mitochondrion | IDA GO_REF:0000052 | ACCEPT | Summary: HPA immunofluorescence data supporting mitochondrial localization. Reason: Direct experimental evidence for mitochondrial localization is consistent with the known function of BOLA3 in the mitochondrial ISC assembly pathway. |
| GO:0005739 mitochondrion | NAS PMID:22746225 BOLA1 is an aerobic protein that prevents mitochondrial morp... | ACCEPT | Summary: This study primarily characterized BOLA1 but also demonstrated that the BolA family proteins are mitochondrial. BOLA3 was mentioned in the context of mitochondrial Fe-S cluster biogenesis. Reason: The study provides supporting evidence for mitochondrial localization of the BolA family proteins, consistent with their role in mitochondrial ISC assembly. Supporting Evidence: PMID:22746225 BOLA3 has recently been implicated in the biogenesis of [Fe-S] clusters for oxidative phosphorylation complexes and 2-oxo acid dehydrogenase enzymes in mitochondria |
| GO:0006879 intracellular iron ion homeostasis | NAS PMID:27532772 Mitochondrial Bol1 and Bol3 function as assembly factors for... | KEEP AS NON CORE | Summary: The BOLA3-GLRX5 complex functions in Fe-S cluster assembly, which indirectly affects iron homeostasis. However, BOLA3's primary role is in Fe-S cluster biogenesis rather than direct iron sensing or trafficking. Reason: While BOLA3 does influence iron homeostasis through its role in Fe-S cluster assembly, this is a downstream consequence rather than the core function. The primary role is in [4Fe-4S] cluster assembly. Supporting Evidence: PMID:27532772 Bol1 and Bol3 as specific mitochondrial ISC assembly factors |
| GO:0016226 iron-sulfur cluster assembly | NAS PMID:27532772 Mitochondrial Bol1 and Bol3 function as assembly factors for... | ACCEPT | Summary: BOLA3 functions in the late phase of mitochondrial Fe-S cluster assembly, specifically facilitating [4Fe-4S] cluster insertion into target proteins. The GLRX5-BOLA3 complex delivers [2Fe-2S] clusters to NFU1 for [4Fe-4S] assembly (PMID:27532772). Reason: This is a core function annotation. BOLA3 is a bona fide Fe-S cluster assembly factor as demonstrated by biochemical and genetic studies. The NAS evidence appropriately reflects the complex molecular pathway. Supporting Evidence: PMID:27532772 we characterize the BOLA family proteins Bol1 and Bol3 as specific mitochondrial ISC assembly factors that facilitate [4Fe-4S] cluster insertion into a subset of mitochondrial proteins such as lipoate synthase and succinate dehydrogenase |
| GO:0045454 cell redox homeostasis | NAS PMID:27532772 Mitochondrial Bol1 and Bol3 function as assembly factors for... | KEEP AS NON CORE | Summary: BolA proteins interact with glutaredoxins and have been implicated in redox regulation. However, the primary characterized function of BOLA3 is in Fe-S cluster assembly rather than direct redox regulation. Reason: This annotation likely reflects the association with GLRX5, a glutaredoxin. While the BOLA3-GLRX5 interaction is functionally important, the primary role is in Fe-S cluster transfer rather than redox homeostasis per se. Supporting Evidence: PMID:22746225 A measured interaction of BOLA1 with the mitochondrial monothiol glutaredoxin GLRX5 provides hints for potential mechanisms behind BOLA1's effect on mitochondrial redox potential PMID:27532772 Mitochondrial Bol1 and Bol3 function as assembly factors for specific iron-sulfur proteins. |
| GO:0005739 mitochondrion | HTP PMID:34800366 Quantitative high-confidence human mitochondrial proteome an... | ACCEPT | Summary: High-confidence human mitochondrial proteome study confirms mitochondrial localization. Reason: HTP proteomics evidence is consistent with other evidence for mitochondrial localization of BOLA3. Supporting Evidence: PMID:34800366 Epub 2021 Nov 19. Quantitative high-confidence human mitochondrial proteome and its dynamics in cellular context. |
| GO:0005739 mitochondrion | IDA PMID:22746225 BOLA1 is an aerobic protein that prevents mitochondrial morp... | ACCEPT | Summary: Direct experimental evidence from the Willems et al. study that characterized BolA family proteins as mitochondrial. Reason: IDA evidence for mitochondrial localization is well-supported and consistent with BOLA3's role in the mitochondrial ISC pathway. Supporting Evidence: PMID:22746225 BOLA1 is a mitochondrial protein |
| GO:0051537 2 iron, 2 sulfur cluster binding | IDA PMID:27532772 Mitochondrial Bol1 and Bol3 function as assembly factors for... | NEW | Summary: BOLA3 binds a [2Fe-2S] cluster as part of the GLRX5-BOLA3 heterocomplex. NMR and spectroscopic studies demonstrate that BOLA3 Cys59 and His96 serve as cluster ligands (PMID:27532772, PMID:34063696). Reason: This is a core molecular function that is well-characterized but not present in the current annotation set. The [2Fe-2S] cluster binding is essential for BOLA3's function as a cluster carrier. Supporting Evidence: PMID:27532772 residues Cys59 and His96 are conserved within the BOLA3 proteins PMID:34063696 C59Y BOLA3-GLRX5 Complex Bound a [2Fe-2S]2+ Cluster |
| GO:0044572 [4Fe-4S] cluster assembly | IMP PMID:27532772 Mitochondrial Bol1 and Bol3 function as assembly factors for... | NEW | Summary: BOLA3 deficiency causes defects in [4Fe-4S] enzyme activities, demonstrating its role in [4Fe-4S] cluster assembly. The GLRX5-BOLA3 complex delivers [2Fe-2S] clusters to NFU1 for [4Fe-4S] assembly. Reason: This is a more specific term than GO:0016226 (iron-sulfur cluster assembly) and accurately reflects BOLA3's role in the late ISC pathway for [4Fe-4S] protein maturation. Supporting Evidence: PMID:27532772 Deficiency of both mitochondrial Bol proteins causes defects in a subset of mitochondrial [4Fe-4S] enzymes |
| GO:1990229 iron-sulfur cluster assembly complex | IDA PMID:27532772 Mitochondrial Bol1 and Bol3 function as assembly factors for... | NEW | Summary: BOLA3 is a component of the mitochondrial BOLA3-GLRX5 iron-sulfur cluster assembly complex (ComplexPortal:CPX-6863). This complex functions in Fe-S cluster transfer. Reason: ComplexPortal has curated the BOLA3-GLRX5 complex and this annotation appropriately reflects BOLA3's participation in this assembly complex. Supporting Evidence: PMID:27532772 In order to characterize the interaction between BOLA1 or BOLA3 and GLRX5 at the atomic level |
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Download this section (compressed HTML)Q: What is the relative contribution of BOLA3 vs BOLA1 to different [4Fe-4S] client proteins? Uzarska et al. showed Bol1 and Bol3 have overlapping but distinct client specificities. Understanding this would help interpret MMDS2 pathophysiology.
Q: Does BOLA3 have functions independent of the GLRX5-BOLA3 heterocomplex? Some interactions detected in HTP studies may represent additional BOLA3 functions not yet characterized.
Experiment: Systematic identification of all BOLA3-dependent [4Fe-4S] client proteins using proteomics in BOLA3-deficient cells. This would provide comprehensive understanding of BOLA3's role in [4Fe-4S] protein maturation beyond known clients like LIAS and SDH.
Hypothesis: BOLA3 deficiency affects specific subset of mitochondrial [4Fe-4S] enzymes that can be comprehensively identified by proteomics.
Experiment: Structure determination of the BOLA3-GLRX5-[2Fe-2S]-NFU1 transfer complex. This would reveal mechanism of [2Fe-2S] cluster transfer from BOLA3-GLRX5 to NFU1 for [4Fe-4S] assembly.
Hypothesis: BOLA3-GLRX5 complex directly interacts with NFU1 during cluster transfer, forming a transient ternary complex.
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