Affinage

BOLA3

BolA-like protein 3 · UniProt Q53S33

Length
107 aa
Mass
12.1 kDa
Annotated
2026-04-28
18 papers in source corpus 12 papers cited in narrative 12 extracted findings

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

BOLA3 is a mitochondrial iron-sulfur (Fe-S) cluster trafficking factor that bridges Fe-S cluster biogenesis to the maturation of respiratory chain complexes, lipoic acid-dependent enzymes, and the mitoribosome. BOLA3 forms a [2Fe-2S] cluster-bridged heterocomplex with the monothiol glutaredoxin GLRX5, which accepts clusters from upstream donors (ISCU) and delivers them downstream to NFU1 for [4Fe-4S] cluster assembly on respiratory chain complexes I and II and lipoic acid synthetase, as well as directly to the mitoribosome small subunit for mitochondrial protein synthesis (PMID:28483642, PMID:30137089, PMID:37511493, PMID:37823603). Disease-causing mutations in BOLA3 (e.g., Ile67Asn, His96Arg) disrupt either GLRX5 binding or cluster coordination within the heterocomplex, abolishing downstream [4Fe-4S] assembly on NFU1 and causing combined deficiency of respiratory chain complexes I, II, and III, pyruvate dehydrogenase, glycine cleavage enzyme, and lipoylation, while sparing aconitase (PMID:33693876, PMID:37511493, PMID:40273865). Biallelic loss-of-function mutations in BOLA3 cause multiple mitochondrial dysfunctions syndrome type 2 (MMDS2), a severe disorder characterized by combined respiratory chain and lipoylation defects (PMID:21944046, PMID:22562699, PMID:24334290).

Mechanistic history

Synthesis pass · year-by-year structured walk · 8 steps
  1. 2011 High

    Establishing that BOLA3 is essential for Fe-S cluster-dependent maturation of respiratory chain complexes and lipoate-containing enzymes resolved the genetic basis of a combined mitochondrial dysfunction syndrome and identified a new Fe-S biogenesis factor.

    Evidence Retroviral complementation of BOLA3-mutant patient fibroblasts with isoform-specific constructs; biochemical enzyme assays

    PMID:21944046

    Open questions at the time
    • Molecular mechanism of BOLA3 action unknown
    • Direct protein partners unidentified
    • Whether BOLA3 acts at [2Fe-2S] or [4Fe-4S] stage undetermined
  2. 2012 High

    Independent replication confirmed BOLA3 loss causes combined respiratory chain and lipoylation deficiency, and demonstrated that wild-type BOLA3 restores lipoic acid levels, cementing the link between Fe-S biogenesis and lipoate biosynthesis.

    Evidence Exome sequencing of new patients; lentiviral complementation; lipoic acid quantification in patient fibroblasts

    PMID:22562699 PMID:24334290

    Open questions at the time
    • Physical interaction partners not identified
    • Whether glycine cleavage system impairment is direct or indirect through lipoylation unclear
  3. 2017 High

    Biophysical reconstitution of the BOLA3-GLRX5 [2Fe-2S]-bridged heterocomplex defined the molecular species through which BOLA3 acts, revealing it coordinates an oxidized ferredoxin-like [2Fe-2S]²⁺ cluster distinct from the BOLA1-GLRX5 complex.

    Evidence UV/vis, CD, EPR, NMR spectroscopy and computational docking of purified human proteins

    PMID:28483642

    Open questions at the time
    • Direction of cluster flow (donor vs. acceptor) not yet demonstrated
    • In vivo relevance of heterocomplex not confirmed
  4. 2018 High

    Quantitative in vitro cluster transfer experiments established that the BOLA3-GLRX5 heterocomplex functions as a bona fide trafficking intermediate, accepting [2Fe-2S] clusters from ISCU and transferring them to downstream acceptors, and revealed weak binding of apo BOLA3 to NFU1.

    Evidence In vitro cluster transfer kinetics; isothermal titration calorimetry; UV/vis spectroscopy

    PMID:30137089

    Open questions at the time
    • Whether BOLA3-GLRX5 directly provides clusters to NFU1 for [4Fe-4S] assembly not shown
    • BOLA3 homodimer physiological relevance unclear
  5. 2021 High

    Structural and biochemical analysis of disease-causing mutations (Ile67Asn, Cys59Tyr) revealed that pathogenicity operates through distinct mechanisms — loss of GLRX5 binding versus perturbation of the cluster-binding site — explaining genotype-phenotype variability.

    Evidence NMR, native MS, EPR spectroscopy, and in vitro cluster reconstitution with mutant BOLA3 proteins

    PMID:33693876 PMID:34063696

    Open questions at the time
    • In vivo validation of mutant complex formation not performed
    • Whether aberrant apo complex has gain-of-function effects unknown
  6. 2023 High

    The His96Arg mutation demonstrated that His96 is a critical [2Fe-2S] cluster ligand in the heterocomplex and that [4Fe-4S] cluster assembly on NFU1 lies directly downstream of the BOLA3-GLRX5 node, ordering the pathway from [2Fe-2S] trafficking to [4Fe-4S] maturation.

    Evidence Size exclusion chromatography, NMR, EPR, CD spectroscopy, and in vitro [4Fe-4S] cluster assembly assay on NFU1

    PMID:37511493

    Open questions at the time
    • Complete set of cluster ligands in the heterocomplex not fully resolved
    • Whether BOLA3-GLRX5 directly donates to NFU1 or requires additional intermediates in vivo unknown
  7. 2023 High

    Discovery that the mitoribosome receives [2Fe-2S] clusters from the GLRX5-BOLA3 node expanded BOLA3 function beyond respiratory chain and lipoylation to mitochondrial translation, and revealed redox-sensing by a mitoribosomal [2Fe-2S] cluster as a regulatory mechanism.

    Evidence siRNA knockdown of Fe-S factors; mitoribosome stability and translation assays in BOLA3-mutant patient fibroblasts

    PMID:37823603

    Open questions at the time
    • Identity of the mitoribosomal [2Fe-2S] acceptor protein not specified
    • Whether translation defect contributes to respiratory chain loss or is independent phenotype unclear
  8. 2025 Medium

    Metabolomic profiling of BOLA3-deficient cells defined pathway specificity: BOLA3 is required for [4Fe-4S] delivery to complexes I, II, and lipoic acid synthetase but not for aconitase maturation, distinguishing BOLA3 from other late-acting Fe-S factors.

    Evidence CE-TOF-MS metabolomics, BN-PAGE, and in-gel enzyme activity in patient fibroblasts

    PMID:40273865

    Open questions at the time
    • Mechanism by which aconitase escapes BOLA3 dependence not explained
    • Single-lab metabolomic study without independent replication

Open questions

Synthesis pass · forward-looking unresolved questions
  • The structural basis of the intact [2Fe-2S]-BOLA3-GLRX5 heterocomplex, the mechanism by which it selectively delivers clusters to NFU1 versus the mitoribosome, and whether the BOLA3 homodimer has a physiological role remain unresolved.
  • No high-resolution structure of the holo BOLA3-GLRX5 heterocomplex
  • Selectivity mechanism for [2Fe-2S] delivery to mitoribosome vs. NFU1 unknown
  • Physiological relevance of BOLA3 homodimer not established in vivo

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0140104 molecular carrier activity 4
Localization
GO:0005739 mitochondrion 5
Pathway
R-HSA-1430728 Metabolism 6 R-HSA-1643685 Disease 4
Partners
GLRX5ISCUNFU1
Complex memberships
BOLA3-GLRX5 [2Fe-2S]-bridged heterocomplex

Evidence

Reading pass · 12 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2011 BOLA3 is required for the biogenesis of iron-sulfur ([Fe-S]) clusters necessary for normal maturation of lipoate-containing 2-oxoacid dehydrogenases and assembly of mitochondrial respiratory chain complexes I, II, and III. Retroviral transduction with the mitochondrial isoform 1 (but not isoform 2) of BOLA3 rescued both respiratory chain function and oxoacid dehydrogenase activity in patient fibroblasts. Retroviral complementation of patient fibroblasts with isoform-specific BOLA3 constructs; biochemical enzyme activity assays American journal of human genetics High 21944046
2012 A homozygous missense mutation in BOLA3 causes combined deficiency of respiratory chain complexes I, II, and II+III and pyruvate dehydrogenase complex; lentiviral expression of wild-type mitochondrial BOLA3 isoform in patient fibroblasts restored residual enzyme activities and lipoic acid levels, confirming BOLA3's role in Fe-S cluster biogenesis and lipoylation. Exome sequencing; lentiviral complementation; biochemical enzyme activity assays; lipoic acid quantification Journal of inherited metabolic disease High 22562699
2013 BOLA3 mutations cause deficiency of lipoylation of mitochondrial proteins and deficient glycine cleavage enzyme activity, impacting lipoate-dependent enzymes including pyruvate dehydrogenase; transfection with native BOLA3 corrected the biochemical deficiency, demonstrating its essential role in lipoate biosynthesis. Genetic sequencing; cell transfection complementation; lipoylation assay; enzyme activity measurement Brain : a journal of neurology High 24334290
2017 Human mitochondrial BOLA3 forms a [2Fe-2S] cluster-bridged dimeric heterocomplex with the monothiol glutaredoxin GRX5. The BOLA3-GRX5 complex coordinates an oxidized, ferredoxin-like [2Fe-2S]2+ cluster, in contrast to the reduced Rieske-type [2Fe-2S]1+ cluster found in the BOLA1-GRX5 complex. The BOLA1-GRX5 complex has higher cluster binding affinity than BOLA3-GRX5. UV/vis, CD, EPR, NMR spectroscopy; computational protein-protein docking; in vitro reconstitution of complexes Biochimica et biophysica acta. General subjects High 28483642
2018 The [2Fe-2S] cluster-bridged BOLA3-GLRX5 heterocomplex functions as a cluster trafficking intermediate: apo BOLA3-glutaredoxin complexes accept [2Fe-2S] clusters from donors (ISCU and [2Fe-2S](GS)4), preferentially forming the heterodimer over the holo glutaredoxin homodimer; holo BOLA3-GLRX5 transfers clusters to apo acceptors at rates comparable to other Fe-S trafficking proteins. ITC confirmed strong binding of apo BOLA3 with GLRX5 and weak binding with NFU1. In vitro cluster transfer assays; isothermal titration calorimetry (ITC); UV/vis spectroscopy Metallomics : integrated biometal science High 30137089
2019 Human BOLA3 can form a functional [2Fe-2S]-bridged homodimer capable of Fe-S cluster binding and inter-protein cluster transfer, in addition to its known heterodimeric interactions with GLRX5 and NFU1. In vitro reconstitution; spectroscopic characterization; cluster transfer assays Journal of biological inorganic chemistry : JBIC Medium 31486956
2021 The disease-causing Ile67Asn substitution in BOLA3 impairs the ability of BOLA3 to bind its physiological partner GLRX5 and prevents formation of the [2Fe-2S]-bridged heterocomplex, thereby blocking downstream cluster reconstitution, without causing major overall structural changes to BOLA3 itself. 1H-15N HSQC NMR; ion mobility native mass spectrometry; in vitro cluster reconstitution assays Metallomics : integrated biometal science High 33693876
2021 The Cys59Tyr BOLA3 mutation structurally perturbs the [2Fe-2S] cluster-binding region of BOLA3 without abolishing cluster binding on the BOLA3-GLRX5 heterocomplex; Tyr59 does not replace Cys59 as a cluster ligand, but promotes formation of an aberrant apo BOLA3-GLRX5 complex, explaining the unique milder clinical phenotype. NMR; UV/vis, CD, EPR spectroscopy; experimentally driven molecular docking; size exclusion chromatography International journal of molecular sciences High 34063696
2021 BOLA3 deficiency in beige adipocytes inhibits thermogenesis by impairing mitochondrial homeostasis (reduced respiratory chain complexes and mitochondrial formation) and adrenergic signaling-induced lipolysis, without affecting lipogenesis. Lentiviral shRNA knockdown in differentiated beige adipocytes; Seahorse respirometry; Western blot for respiratory chain complexes; lipolysis assay Frontiers in endocrinology Medium 33505355
2023 The His96Arg BOLA3 mutation does not impair BOLA3-GLRX5 interaction but leads to an aberrant [2Fe-2S]-BOLA3-GLRX5 heterocomplex that cannot assemble a [4Fe-4S] cluster on NFU1, establishing that His96 is a critical [2Fe-2S] cluster ligand in the BOLA3-GLRX5 complex and that [4Fe-4S] delivery to NFU1 is downstream of the BOLA3-GLRX5 node. Size exclusion chromatography; NMR; UV/vis; CD; EPR spectroscopy; in vitro [4Fe-4S] cluster assembly assay on NFU1 International journal of molecular sciences High 37511493
2023 The mitoribosome receives its [2Fe-2S] clusters from the GLRX5-BOLA3 node; loss of BOLA3 attenuates mitochondrial protein synthesis through impaired [2Fe-2S] cluster assembly into the mitoribosome small subunit. One of the mitoribosomal [2Fe-2S] clusters senses changes in the redox environment, providing a regulatory mechanism for organellar protein synthesis. siRNA silencing of Fe-S cluster biosynthetic factors; mitoribosome stability assays; mitochondrial protein synthesis assays in BOLA3-mutant patient fibroblasts; structure-function correlation studies Nucleic acids research High 37823603
2025 Metabolomic analysis of BOLA3-deficient patient fibroblasts shows elevated lactic acid, pyruvic acid, TCA cycle intermediates (α-ketoglutaric acid, succinic acid), branched-chain amino acids, and lysine/tryptophan metabolites, with near-absent complex I and II bands; aconitase activity is unaffected. This defines BOLA3 as specifically involved in [4Fe-4S] cluster delivery to respiratory chain complexes I and II and lipoic acid synthetase, but not aconitase. Capillary electrophoresis time-of-flight mass spectrometry metabolomics; BN-PAGE/Western blot; in-gel enzyme staining of mitochondrial complexes in patient fibroblasts Molecular genetics and metabolism Medium 40273865

Source papers

Stage 0 corpus · 18 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2011 Mutations in iron-sulfur cluster scaffold genes NFU1 and BOLA3 cause a fatal deficiency of multiple respiratory chain and 2-oxoacid dehydrogenase enzymes. American journal of human genetics 220 21944046
2013 Variant non ketotic hyperglycinemia is caused by mutations in LIAS, BOLA3 and the novel gene GLRX5. Brain : a journal of neurology 170 24334290
2012 Homozygous missense mutation in BOLA3 causes multiple mitochondrial dysfunctions syndrome in two siblings. Journal of inherited metabolic disease 75 22562699
2017 Structural insights into the molecular function of human [2Fe-2S] BOLA1-GRX5 and [2Fe-2S] BOLA3-GRX5 complexes. Biochimica et biophysica acta. General subjects 44 28483642
2023 BOLA3 and NFU1 link mitoribosome iron-sulfur cluster assembly to multiple mitochondrial dysfunctions syndrome. Nucleic acids research 26 37823603
2018 Cluster exchange reactivity of [2Fe-2S] cluster-bridged complexes of BOLA3 with monothiol glutaredoxins. Metallomics : integrated biometal science 20 30137089
2018 An infant case of diffuse cerebrospinal lesions and cardiomyopathy caused by a BOLA3 mutation. Brain & development 19 29501406
2018 Imaging phenotype of multiple mitochondrial dysfunction syndrome 2, a rare BOLA3-associated leukodystrophy. American journal of medical genetics. Part A 13 30302924
2021 Bola3 Regulates Beige Adipocyte Thermogenesis via Maintaining Mitochondrial Homeostasis and Lipolysis. Frontiers in endocrinology 12 33505355
2018 Severe Leukoencephalopathy with Clinical Recovery Caused by Recessive BOLA3 Mutations. JIMD reports 11 29654549
2021 Molecular Basis of Multiple Mitochondrial Dysfunctions Syndrome 2 Caused by CYS59TYR BOLA3 Mutation. International journal of molecular sciences 8 34063696
2019 Reconstitution, characterization, and [2Fe-2S] cluster exchange reactivity of a holo human BOLA3 homodimer. Journal of biological inorganic chemistry : JBIC : a publication of the Society of Biological Inorganic Chemistry 4 31486956
2021 Biochemical impact of a disease-causing Ile67Asn substitution on BOLA3 protein. Metallomics : integrated biometal science 2 33693876
2024 Dysregulated inclusion of BOLA3 exon 3 promoted by HNRNPC accelerates the progression of esophageal squamous cell carcinoma. Frontiers of medicine 1 39455467
2023 Understanding the Molecular Basis of the Multiple Mitochondrial Dysfunctions Syndrome 2: The Disease-Causing His96Arg Mutation of BOLA3. International journal of molecular sciences 1 37511493
2025 Exploring the potential of BOLA3-DT as a diagnostic biomarker in prostate cancer. Urologia 0 39849679
2025 Role of BOLA3 in the mitochondrial Fe-S cluster clarified by metabolomic analysis. Molecular genetics and metabolism 0 40273865
2025 BOLA3 as a key protein for the treatment of diabetic skeletal muscle atrophy. International immunopharmacology 0 40850197