BOLA3 is a mitochondrial BolA-family protein that contributes to late iron-sulfur protein maturation. It forms a [2Fe-2S]-binding heterocomplex with the monothiol glutaredoxin GLRX5. Reconstituted human-protein experiments link this complex to cluster transfer and formation of [4Fe-4S]-bound NFU1, although reports differ on direct binding between isolated BOLA3 and NFU1. Mitochondrial Bol function is especially important for lipoic acid synthase maturation and protein lipoylation. Yeast loss-and-rescue experiments also link it to succinate dehydrogenase activity, and BOLA3-deficient patient cells show respiratory-complex I and II deficiencies. BOLA3 provides cluster-binding and transfer-associated function rather than lipoic-acid synthesis itself. Pathogenic variants cause multiple mitochondrial dysfunctions syndrome 2, with impaired lipoylation and mitochondrial energy metabolism; individual variants can retain partial biochemical activity.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0051604 protein maturation | IBA GO_REF:0000033 | ACCEPT | Summary: BOLA3 contributes to maturation of mitochondrial iron-sulfur proteins (PMID:27532772). Reason: Yeast loss-and-rescue experiments and human BOLA3 biochemistry support late Fe-S protein maturation (PMID:27532772). This is compatible with the PAINT assertion at PANTHER:PTN001763701; no target-specific loss or erroneous ancestral placement is established. Protein maturation and iron-sulfur cluster assembly describe compatible levels of this role. Supporting Evidence: PMID:27532772 insertion of [4Fe-4S] clusters into target apoproteins |
| GO:0005759 mitochondrial matrix | IBA GO_REF:0000033 | ACCEPT | Summary: The mitochondrial matrix is consistent with BOLA3 function in the mitochondrial ISC system (PMID:27532772). Reason: Retain the PAINT inference at PANTHER:PTN001763701. PMID:27532772 directly localizes yeast Bol3 to the matrix by fractionation and protease protection, and studies human BOLA3 interactions with mitochondrial ISC partners. This supports the conserved compartment; it is not a new direct human localization experiment. The BOLA1-specific localization sentence in PMID:22746225 is not used as BOLA3 proof. Supporting Evidence: PMID:27532772 Bol1 and Bol3 are constituents of the mitochondrial matrix. |
| GO:0005739 mitochondrion | IEA GO_REF:0000120 | ACCEPT | Summary: Mitochondrial localization is compatible with the reviewed BOLA3 record and its ISC function (PMID:27532772). Reason: The combined electronic annotation is broader than the matrix IBA but biologically consistent. Retain the machine-sourced assertion. Independent support includes the other curated mitochondrial annotations and the mitochondrial ISC role; no claim is made that the BOLA1 experiments in PMID:22746225 directly assay BOLA3. |
| GO:0005515 protein binding | IPI PMID:27499296 Mitochondrial Protein Interaction Mapping Identifies Regulat... | KEEP AS NON CORE | Summary: The source IPI records a BOLA3 interaction with GLRX5 (UniProtKB:Q86SX6; PMID:27499296). Reason: The source IPI names GLRX5/Q86SX6. Human BOLA3–GLRX5 binding is independently established by biochemical experiments in PMID:27532772 and PMID:34063696, supporting non-core retention with curator deference to the original interaction record. The original mapping-table experiment is unverified; corroboration does not certify that experiment. Protein-partner binding and 2Fe-2S cofactor binding are distinct molecular assertions. |
| GO:0005515 protein binding | IPI PMID:27532772 Mitochondrial Bol1 and Bol3 function as assembly factors for... | KEEP AS NON CORE | Summary: This source row includes BOLA3 interactions with processed GLRX5 and with NFU1 (PMID:27532772). Reason: The source records name processed GLRX5/UniProtKB:Q86SX6-PRO_0000141650 and NFU1/UniProtKB:Q9UMS0. In PMID:27532772, NMR detects GLRX5–BOLA3 interaction, whereas size-exclusion chromatography does not resolve a stable holo heterodimer and CD shows a weak, GSH-dependent response without cluster stabilization. Thus the interaction is condition-dependent. Microscale thermophoresis reports preferential BOLA3 binding to holo-NFU1, but PMID:34063696 summarizes later no-interaction results for isolated apo/holo BOLA3 and NFU1. The valid GLRX5 interaction supports retaining generic binding while preserving this NFU1 disagreement; neither a permanent ternary complex nor an exclusive cellular route follows. |
| GO:0005515 protein binding | IPI PMID:32296183 A reference map of the human binary protein interactome. | UNDECIDED | Summary: The seven-partner HuRI BOLA3 assertion remains unresolved; independent GLRX5 biochemistry does not establish the original screen observations (PMID:32296183). Reason: The preserved partners are GLRX3/O76003, KRT34/O76011, MAGEA6/P43360, INCA1/Q0VD86, GLRX5/Q86SX6, RAB17/Q9H0T7 and PICK1/Q9NRD5. Separate human biochemical studies establish BOLA3–GLRX5 association (PMID:27532772; PMID:34063696), but the original HuRI BOLA3 edge/table and assay context remain uninspected, and the other six partner interactions remain unverified. That corroboration does not resolve this source-specific aggregate. Keep the assertion undecided without treating genericity, screen origin or missing inspection as evidence that the interactions are false. |
| GO:0005515 protein binding | IPI PMID:33961781 Dual proteome-scale networks reveal cell-specific remodeling... | UNDECIDED | Summary: The source IPI partner is FAAP100 (UniProtKB:Q0VG06), rather than GLRX5 (PMID:33961781). Reason: FAAP100/UniProtKB:Q0VG06 is the source partner, so independently established GLRX5 binding cannot adjudicate this distinct interaction. The target-specific AP-MS experiment, orientation and cellular context remain unverified. Retain the source assertion as undecided; the generic term and screen origin do not themselves make the interaction false. |
| GO:0005515 protein binding | IPI PMID:34063696 Molecular Basis of Multiple Mitochondrial Dysfunctions Syndr... | KEEP AS NON CORE | Summary: Human wild-type and C59Y BOLA3 interact with GLRX5, with variant-dependent changes in the interaction surface (PMID:34063696). Reason: Results section 2.2 compares wild-type and C59Y proteins by reciprocal NMR titration. C59Y retains heterocomplex formation but alters contacts at the higher concentration examined; this is not complete loss of binding. Protein interaction and the cluster coordination assays in section 2.3 support distinct molecular assertions, so the protein-partner IPI remains non-core. |
| GO:0005739 mitochondrion | IDA GO_REF:0000052 | ACCEPT | Summary: The curated immunofluorescence annotation places BOLA3 in mitochondria (GO_REF:0000052). Reason: The source immunofluorescence IDA agrees with the established mitochondrial ISC role and independent mitochondrial annotations. Retention uses curator deference for the underlying imaging; it does not add a new localization experiment. |
| GO:0005739 mitochondrion | NAS PMID:22746225 BOLA1 is an aerobic protein that prevents mitochondrial morp... | ACCEPT | Summary: PMID:22746225 discusses BOLA3 in mitochondrial Fe-S biogenesis while principally studying BOLA1. Reason: The cached Introduction specifically mentions BOLA3 in mitochondrial oxidative-phosphorylation and 2-oxo-acid-dehydrogenase Fe-S biogenesis. This supports the mitochondrial context of the NAS assertion. The paper’s BOLA1 localization and redox experiments must not be generalized to BOLA3. Retain the biologically established location without claiming all BolA-family proteins were directly localized here. Supporting Evidence: PMID:22746225 BOLA3 has recently been implicated in the biogenesis of [Fe-S] clusters |
| GO:0006879 intracellular iron ion homeostasis | NAS PMID:27532772 Mitochondrial Bol1 and Bol3 function as assembly factors for... | UNDECIDED | Summary: The relationship between human BOLA3 and intracellular iron homeostasis remains unresolved (PMID:27532772). Reason: Bol1/Bol3 deletion does not alter the tested yeast iron-regulon response, distinguishing their late Fe-S assembly role from cytosolic Bol2-dependent regulation. This is a negative result for a particular organism and endpoint, not a refutation of every human intracellular iron-homeostasis mechanism. Conversely, Fe-S maturation and Bol2-dependent metabolic crosstalk alone do not establish the particular human BOLA3 regulatory contribution. The human role asserted by this NAS annotation therefore remains uncertain rather than positively supported or generally contradicted. |
| GO:0016226 iron-sulfur cluster assembly | NAS PMID:27532772 Mitochondrial Bol1 and Bol3 function as assembly factors for... | ACCEPT | Summary: BOLA3 participates in the late mitochondrial iron-sulfur protein assembly pathway (PMID:27532772, PMID:34063696). Reason: PMID:27532772 combines yeast loss/rescue and Fe-S-protein measurements with human GLRX5/BOLA3 and NFU1 interaction studies, identifying a late role especially in LIAS maturation. The human NMR transfer comparison in PMID:34063696 section 2.3 additionally follows formation of cluster-bound NFU1 with wild-type versus C59Y BOLA3–GLRX5. BOLA3 supplies cluster-binding and transfer-associated function rather than catalyzing lipoic-acid synthesis itself. Retain the broad assembly annotation. The 2016 study alone did not demonstrate the complete GLRX5-to-NFU1 transfer scheme. Supporting Evidence: PMID:27532772 mitochondrial ISC assembly factors |
| GO:0045454 cell redox homeostasis | NAS PMID:27532772 Mitochondrial Bol1 and Bol3 function as assembly factors for... | UNDECIDED | Summary: Direct BOLA3 participation in cell redox homeostasis is unresolved from the cited evidence (PMID:27532772). Reason: A human BOLA3 contribution to cellular redox balance cannot be resolved from the available mechanistic evidence. BOLA1-dependent redox phenotypes and the redox sensitivity of reconstituted BOLA3–GLRX5 clusters address different proteins or levels of organization. They neither establish a BOLA3 cellular homeostasis mechanism nor exclude one. The NAS assertion remains undecided without treating glutaredoxin association as sufficient positive evidence or extrapolating a negative cellular conclusion from an in vitro stability assay. |
| GO:0005739 mitochondrion | HTP PMID:34800366 Quantitative high-confidence human mitochondrial proteome an... | ACCEPT | Summary: The curated HTP annotation places BOLA3 in the human mitochondrial proteome (PMID:34800366). Reason: The study combines subtractive proteomics, spatial profiling and importomics in human cells. Its source-curated mitochondrial placement agrees with BOLA3 biology, so the HTP annotation is retained with curator deference; the exact BOLA3 measurement is not independently verified. |
| GO:0005739 mitochondrion | IDA PMID:22746225 BOLA1 is an aerobic protein that prevents mitochondrial morp... | ACCEPT | Summary: The source IDA reports mitochondrial localization for BOLA3 (PMID:22746225). Reason: BOLA3 mitochondrial localization is biologically established, supporting retention of this source IDA with curator deference. The visible BOLA1 localization experiment is not used as direct BOLA3 evidence, and the original BOLA3-specific assay remains unverified. |
| 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 in the human GLRX5–BOLA3 heterocomplex (PMID:27532772, PMID:34063696). Reason: Human holo-complex reconstitution and NMR/spectroscopy support it; PMID:34063696 directly compares wild-type and C59Y holo-complexes. Conservation of Cys59/His96 alone is not the evidence for binding. C59Y perturbs coordination but retains cluster binding, and Tyr59 does not simply substitute as a ligand. This function is distinct from the retained IPI protein-partner interactions. Supporting Evidence: PMID:34063696 the [2Fe–2S]2+ BOLA3–GLRX5 complex |
| GO:1990229 iron-sulfur cluster assembly complex | IDA PMID:27532772 Mitochondrial Bol1 and Bol3 function as assembly factors for... | NEW | Summary: BOLA3 forms a mitochondrial iron-sulfur assembly heterocomplex with GLRX5 (PMID:27532772, PMID:34063696). Reason: PMID:34063696 directly compares wild-type and C59Y BOLA3–GLRX5 complexes by reciprocal NMR titration, chemical cluster reconstitution and spectroscopy, supporting a cluster-binding Fe-S assembly heterocomplex. The earlier PMID:27532772 detects interaction by NMR but reports no stable holo heterodimer on size-exclusion chromatography and weak, GSH-dependent CD effects without cluster stabilization. Complex formation therefore does not imply a permanently stable assembly under every condition. GO:1990229 does not require fixed subunit stoichiometry or a ternary NFU1 complex. The UniProt CPX-6863/GO:1990229 cross-references are corroborating curated records; the direct later biochemical evidence is primary here. Supporting Evidence: PMID:34063696 the [2Fe–2S]2+ BOLA3–GLRX5 complex |
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Download this section (compressed HTML)Q: Which human BOLA3–GLRX5 cluster-transfer routes predominate in cells, and how do they relate to NFU1, ISCA1/ISCA2 and individual Fe-S clients? What explains the reported disagreement about direct binding of isolated BOLA3 to NFU1 between the 2016 MST assays and later studies summarized in PMID:34063696? Reconstitution and yeast loss/rescue data do not establish the exclusive human route.
Q: Can the target-specific records for the HuRI BOLA3 partners and the BOLA3–FAAP100 interaction be examined to distinguish validated physical interactions from physiological functions?
Q: Does human BOLA3 perform a sufficiently defined step of [4Fe-4S] cluster assembly to justify GO:0044572 specifically, beyond its supported broad GO:0016226 role? Reconstitution forms the [4Fe-4S] cluster on NFU1, and the limited GLRX5/NFU1/ISCA1/ISCA2 UniProt comparator snapshots do not carry the finer term. Clarify the intended role and avoid adding an ancestor/descendant pair as redundant coverage.
Experiment: Test cluster-transfer and LIAS-maturation phenotypes using human BOLA3 depletion and rescue with wild-type and defined variants, while measuring the relevant complex and Fe-S clients separately.
Hypothesis: Variant-dependent effects on BOLA3 cluster handling alter late Fe-S protein maturation; the relative cellular contribution of the reconstituted GLRX5–BOLA3–NFU1 route remains testable.
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