sod-2 encodes the principal manganese-dependent superoxide dismutase (MnSOD) of the Caenorhabditis elegans mitochondrion. The nuclear-encoded precursor carries an N-terminal mitochondrial transit peptide that directs import into the mitochondrial matrix, where the mature chain assembles into the characteristic iron/manganese superoxide dismutase fold and binds one catalytic Mn(2+) ion per subunit. The enzyme dismutates the superoxide anion radical, a by-product of the respiratory electron transport chain, into hydrogen peroxide and molecular oxygen (2 superoxide + 2 H+ -> H2O2 + O2; EC 1.15.1.1), providing a first line of antioxidant defense within the organelle. C. elegans has a second, closely related mitochondrial MnSOD, sod-3 (~86% identical), which is expressed at low basal levels and is strongly induced by the DAF-16/FOXO branch of insulin/IGF-1 signalling; sod-2 is the constitutively expressed and quantitatively dominant mitochondrial isoform. Beyond bulk matrix scavenging, SOD-2 physically associates with the respiratory-chain supercomplex I:III:IV, positioning it to detoxify superoxide at its site of production and potentially to influence supercomplex stability and complex I/II activity. Counterintuitively for a core antioxidant enzyme, loss of sod-2 does not shorten and in several mitochondrial-mutant backgrounds can extend C. elegans lifespan, a finding central to debates over the role of reactive oxygen species in aging. The enzyme's hydrogen peroxide product also serves as a signalling molecule: it contributes to a RAS-dependent ROS-signalling program linked to longevity and is required for sperm pseudopod extension during sperm activation.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
|
GO:0005739
mitochondrion
|
IBA
GO_REF:0000033 |
KEEP AS NON CORE |
Summary: Phylogenetic (IBA) inference that SOD-2 is active in the mitochondrion. Correct but less specific than the mitochondrial matrix, which is where this MnSOD acts.
Reason: Consistent with the mitochondrial transit peptide and with experimental localization, but generic relative to mitochondrial matrix (GO:0005759), which is retained as the core location. Kept as a correct, less-specific companion term.
|
|
GO:0004784
superoxide dismutase activity
|
IBA
GO_REF:0000033 |
ACCEPT |
Summary: Phylogenetic (IBA) inference of superoxide dismutase activity. This is the core molecular function of SOD-2 and is directly confirmed experimentally.
Reason: SOD-2 is an experimentally validated manganese superoxide dismutase; the IBA call is fully concordant with the IDA evidence (PMID:9353332) and with the Fe/Mn-SOD family assignment. Core function.
Supporting Evidence:
PMID:9353332
The expressed enzymes, which were not inhibited by hydrogen peroxide or cyanide, are dimeric, show quite different electrophoretic mobilities and isoelectric points, but exhibit comparable specific activities.
|
|
GO:0030145
manganese ion binding
|
IBA
GO_REF:0000033 |
ACCEPT |
Summary: Phylogenetic (IBA) inference of manganese ion binding, the catalytic cofactor of this MnSOD. Concordant with the UniProt Mn(2+) cofactor and Mn-ligand residues, and with the enzyme's Mn-type biochemistry.
Reason: Correct and specific metal-binding function: this is a Mn-type (not Fe- or Cu/Zn-type) SOD, insensitive to hydrogen peroxide and cyanide, binding one Mn(2+) per subunit. Core cofactor-binding function.
Supporting Evidence:
PMID:9353332
The expressed enzymes, which were not inhibited by hydrogen peroxide or cyanide, are dimeric, show quite different electrophoretic mobilities and isoelectric points, but exhibit comparable specific activities.
|
|
GO:0004784
superoxide dismutase activity
|
IEA
GO_REF:0000120 |
ACCEPT |
Summary: Electronic (IEA) assignment of superoxide dismutase activity from combined automated methods (ARBA/InterPro/EC/RHEA mapping). Redundant with the experimental IDA and phylogenetic IBA calls for the same core function.
Reason: Same core molecular function as the IDA/IBA annotations; the EC 1.15.1.1 / RHEA:20696 mapping is correct for this enzyme. Retained as concordant supporting evidence.
|
|
GO:0005759
mitochondrial matrix
|
IEA
GO_REF:0000044 |
ACCEPT |
Summary: Electronic (SubCell) localization to the mitochondrial matrix, matching the UniProt subcellular location and the N-terminal mitochondrial transit peptide. This is the core site of SOD-2 action.
Reason: Correct and appropriately specific localization for a matrix MnSOD; supported by the transit peptide and by the primary-mtSOD role. Core location.
Supporting Evidence:
PMID:9353332
Both deduced protein sequences contain the expected N-terminal mitochondrial transit peptides.
|
|
GO:0006801
superoxide metabolic process
|
IEA
GO_REF:0000002 |
KEEP AS NON CORE |
Summary: Electronic (InterPro2GO) assignment to the general superoxide metabolic process. Correct but less specific than removal of superoxide radicals (GO:0019430), which is the experimentally supported process.
Reason: Accurate parent process, but subsumed by the more specific removal of superoxide radicals term retained as core. Kept as a correct, less-informative companion.
|
|
GO:0046872
metal ion binding
|
IEA
GO_REF:0000002 |
KEEP AS NON CORE |
Summary: Electronic (InterPro2GO) generic metal-ion-binding annotation. Subsumed by the specific manganese ion binding (GO:0030145) term.
Reason: Correct but uninformative parent of manganese ion binding; the specific Mn(2+) term is retained as core. Kept as a non-core, less-specific companion.
|
|
GO:0098803
respiratory chain complex
|
IEA
GO_REF:0000117 |
KEEP AS NON CORE |
Summary: Electronic (ARBA) assertion that SOD-2 is part_of the respiratory chain complex. SOD-2 is a soluble matrix MnSOD that physically associates with supercomplex I:III:IV (see the experimental located_in annotation), but it is not a canonical structural subunit of an electron-transport complex, so the part_of qualifier overstates the relationship.
Reason: The experimentally supported relationship is association/co-localization with the I:III:IV supercomplex (PMID:23895727, located_in), consistent with local superoxide scavenging and possible supercomplex stabilization; SOD-2 does not carry out or structurally constitute electron transport. The automated part_of qualifier is an over-generalization, so this is retained only as a non-core companion to the experimental located_in annotation rather than as evidence of structural subunit membership.
Supporting Evidence:
PMID:23895727
Western blots of BNGs indicated that SOD-2 co-localized with the I:III:IV supercomplex (Figure 4D).
|
|
GO:0004784
superoxide dismutase activity
|
IDA
PMID:9353332 Cloning, expression, and characterization of two manganese s... |
ACCEPT |
Summary: Direct assay (IDA) of superoxide dismutase activity: the mature SOD-2 protein was expressed in SOD-deficient E. coli and shown to be an active, Mn-type dismutase. This is the primary experimental evidence for the core function.
Reason: Gold-standard experimental support for the defining molecular function. Insensitivity to hydrogen peroxide and cyanide confirms the Mn-type (not Fe- or Cu/Zn-type) mechanism. Core function.
Supporting Evidence:
PMID:9353332
The expressed enzymes, which were not inhibited by hydrogen peroxide or cyanide, are dimeric, show quite different electrophoretic mobilities and isoelectric points, but exhibit comparable specific activities.
file:worm/sod-2/sod-2-deep-research-falcon.md
Primary mitochondrial Mn-superoxide dismutase that converts superoxide to hydrogen peroxide and oxygen
|
|
GO:0019430
removal of superoxide radicals
|
IMP
PMID:9353332 Cloning, expression, and characterization of two manganese s... |
ACCEPT |
Summary: SOD-2 removes superoxide radicals: heterologous expression of the worm enzyme rescued SOD-deficient E. coli from methyl-viologen (paraquat) oxidative stress. This is the core biological process the enzyme serves.
Reason: Functionally correct core process. The evidence is heterologous complementation (protection of SOD-null E. coli against a superoxide generator) rather than a worm loss-of-function phenotype, but it directly demonstrates superoxide-radical removal by the SOD-2 protein. Core process.
Supporting Evidence:
PMID:9353332
Both proteins were shown to be active in E. coli, providing similar protection against methyl viologen-induced oxidative stress.
|
|
GO:0098803
respiratory chain complex
|
IDA
PMID:23895727 Novel interactions between mitochondrial superoxide dismutas... |
KEEP AS NON CORE |
Summary: Direct assay (IDA) showing SOD-2 co-localizes with mitochondrial supercomplex I:III:IV by blue-native gel Western blotting. A genuine, sod-2-specific localization finding, but a peripheral association rather than the enzyme's core identity.
Reason: Experimentally supported association of SOD-2 with the I:III:IV supercomplex, consistent with local scavenging of superoxide at its site of production and a possible supercomplex-stabilizing role. Retained with the located_in qualifier as a real but non-core localization (SOD-2's core identity is a matrix MnSOD, not a structural ETC subunit).
Supporting Evidence:
PMID:23895727
Western blots of BNGs indicated that SOD-2 co-localized with the I:III:IV supercomplex (Figure 4D).
|
|
GO:0005739
mitochondrion
|
HDA
PMID:20188671 The matrix peptide exporter HAF-1 signals a mitochondrial UP... |
KEEP AS NON CORE |
Summary: High-throughput direct-assay (HDA) mitochondrial-proteome localization of SOD-2. Correct but generic relative to the mitochondrial matrix term.
Reason: Mitochondrial localization of this MnSOD is biologically unambiguous and concordant with the transit peptide and matrix localization; retained as a correct, less-specific companion to mitochondrial matrix (GO:0005759). The cited abstract concerns the mtUPR and does not mention sod-2, so no sod-2-specific verbatim quote is available for the HDA dataset.
|
Q: By what mechanism does loss of the primary mitochondrial antioxidant SOD-2 fail to shorten, and in some backgrounds extend, C. elegans lifespan β is superoxide acting as a pro-longevity signal (mitohormesis), or is the effect mediated by metabolic slowing and supercomplex remodeling?
Q: What is the functional division of labour between the two nearly identical mitochondrial MnSODs, SOD-2 (constitutive, dominant) and SOD-3 (DAF-16-inducible, low basal), given their non-redundant and sometimes opposite genetic interactions with electron-transport-chain mutants?
Q: Is SOD-2's association with respiratory supercomplex I:III:IV purely a positioning device for local superoxide scavenging, or does SOD-2 also act as a structural stabilizer of the supercomplex independent of its catalytic activity?
Experiment: Catalytically-dead (metal-ligand mutant) versus wild-type sod-2 rescue in a sod-2 null, scoring lifespan, complex I/II activity, and supercomplex formation, to separate the scavenging function from a possible structural role.
Experiment: Quantitative, isoform-resolved proteomics and tagged-allele localization of SOD-2 versus SOD-3 across tissues and stress conditions to define their non-redundant contributions and supercomplex occupancy.
Experiment: Genetic-epistasis and redox-biosensor (e.g. mitochondrial roGFP/HyPer) analysis of sod-2 loss in long-lived ETC mutants to test whether a superoxide/ROS signal, rather than bulk oxidative damage, mediates the lifespan extension.
What is not known β curated, literature-grounded statements of the open unknowns (the inverse of core functions).
Gap: How loss of the primary mitochondrial superoxide dismutase SOD-2 extends C. elegans lifespan is only partly resolved. A specific mechanism has been proposed β a RAS-dependent ROS-signalling (RDRS) pathway in which elevated mitochondrial superoxide is converted by cytosolic SOD-1 to hydrogen peroxide that oxidizes a redox-sensitive cysteine of LET-60/RAS β but how much of the longevity effect is attributable to this ROS signal versus to the concurrent reduction in respiration, altered mitochondrial supercomplex stability, and developmental/metabolic slowing remains undetermined, as does why the same loss shortens lifespan once mitochondrial dysfunction exceeds a threshold.
NARROWING BIOLOGY BP_DARK
What is known: It is firmly established that SOD-2 is an active mitochondrial MnSOD and the primary mitochondrial superoxide scavenger, that sod-2 single mutants are not short-lived and are in fact long-lived despite increased protein oxidative damage, that deletion of sod-2 markedly increases lifespan in clk-1 but decreases it in isp-1 backgrounds, that loss of sod-2 lowers complex I/II activity and supercomplex formation, and that a RDRS mechanism requiring SOD-1 can account for part of the extension. What is not established is the causal weighting of the signalling versus metabolic contributions.
Significance: This is a central, counterintuitive case in the debate over the free-radical / oxidative-damage theory of aging: a core antioxidant enzyme whose removal does not shorten and can extend life. Resolving the causal weighting would clarify when mitochondrial superoxide acts as a damaging agent versus a pro-longevity signal.
Provenance (the field's own admissions):
Gap: The functional division of labour between the two nearly identical mitochondrial manganese superoxide dismutases, SOD-2 and SOD-3, is undefined. It is unknown why C. elegans maintains both, what distinguishes their substrates or sub-mitochondrial contexts, and why loss of sod-2 versus sod-3 produces different (sometimes opposite) genetic interactions with electron-transport-chain mutants.
OPEN BIOLOGY RESIDUAL_SUBGAP
What is known: It is established that sod-2 and sod-3 are ~86% identical mitochondrial MnSODs, that sod-2 is constitutively expressed and dominant while sod-3 is expressed at low basal levels and induced by DAF-16/insulin signalling, that both associate with supercomplex I:III:IV, and that they are functionally non-redundant (loss of sod-2 versus sod-3 produces different genetic interactions with ETC mutants, and sod-2 but not sod-1 is specifically required for H2O2-dependent sperm activation). What is not established is the mechanistic basis of the non-redundancy at the level of substrate, sub-mitochondrial context, or partner; the authors of the key ETC study explicitly state that the sod-3/supercomplex relationship was still under investigation.
Significance: Two paralogous mitochondrial MnSODs with divergent, non-redundant phenotypes are a clean model for how gene duplication partitions an antioxidant function; the division of labour also determines which isoform is limiting under which stress.
Provenance (the field's own admissions):
Gap: Whether SOD-2's association with respiratory supercomplex I:III:IV reflects only local superoxide scavenging at the site of ROS production, or whether SOD-2 also acts as a direct structural stabilizer of the supercomplex independent of its catalytic activity, is undetermined.
OPEN BIOLOGY RESIDUAL_SUBGAP
What is known: It is established that SOD-2 co-localizes with the I:III:IV supercomplex by blue-native gel and that sod-2 loss reduces supercomplex formation and complex I activity. The open question is causality/mechanism: complex I function falls out of proportion to the measured ROS damage, so a catalysis-independent structural role remains possible but unproven.
Significance: Distinguishing a scavenging role from a structural role would determine whether MnSOD is a modular antioxidant or an integral stabilizer of the electron transport chain, with implications for how supercomplex integrity is maintained.
Provenance (the field's own admissions):
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.
The gene sod-2 (synonym: sdm-1; ORF name: F10D11.1) in Caenorhabditis elegans encodes Superoxide dismutase [Mn] 1, mitochondrial (EC 1.15.1.1), a member of the iron/manganese superoxide dismutase family. The gene is located on chromosome I and produces a precursor protein that is processed upon mitochondrial import (hunter1997cloningexpressionand pages 1-1). C. elegans possesses five superoxide dismutase genes: the cytoplasmic Cu/ZnSODs sod-1 and sod-5, the mitochondrial MnSODs sod-2 and sod-3, and the extracellular Cu/ZnSOD sod-4 (braeckman2016invivodetection pages 2-3). SOD-2 and SOD-3 are the products of a relatively recent gene duplication event, sharing 86.3% sequence identity (91.8% conservative identity), though their cDNAs are only 75.2% identical and the two proteins display distinct electrophoretic mobilities and isoelectric points (hunter1997cloningexpressionand pages 1-1, hunter1997cloningexpressionand pages 4-5).
The following table summarizes the key biochemical and functional properties of SOD-2:
| Property | SOD-2 summary | Evidence |
|---|---|---|
| Gene name | sod-2; historical synonym sdm-1 | (hunter1997cloningexpressionand pages 6-7, hunter1997cloningexpressionand pages 1-2) |
| Protein name | Manganese superoxide dismutase / mitochondrial superoxide dismutase (MnSOD) | (hunter1997cloningexpressionand pages 6-7, hunter1997cloningexpressionand pages 1-1) |
| UniProt accession | P31161 | (hunter1997cloningexpressionand pages 6-7) |
| Organism | Caenorhabditis elegans | (hunter1997cloningexpressionand pages 6-7, hunter1997cloningexpressionand pages 1-2) |
| Enzyme class | Superoxide dismutase, EC 1.15.1.1 | (hunter1997cloningexpressionand pages 1-1, hunter1997cloningexpressionand pages 1-2) |
| Catalytic reaction | Catalyzes dismutation of superoxide anion (O2β’β) to hydrogen peroxide (H2O2) and oxygen (O2) | (hunter1997cloningexpressionand pages 1-1, sakamoto2017hydrogenperoxideproduced pages 1-2) |
| Physiologic substrate specificity | Primary substrate is superoxide radical generated in mitochondria; product H2O2 can serve signaling roles | (raamsdonk2009deletionofthe pages 2-3, sakamoto2017hydrogenperoxideproduced pages 10-11, branicky2022stimulationofrasdependent pages 2-3) |
| Metal cofactor | Manganese (Mn) | (hunter1997cloningexpressionand pages 6-7, hunter1997cloningexpressionand pages 1-1) |
| Molecular mass, monomer | 21,986 Da, 192 aa mature protein | (hunter1997cloningexpressionand pages 6-7, hunter1997cloningexpressionand pages 5-6) |
| Oligomeric state / dimer mass | Functions as an active dimer; measured mass 44,961 Da | (hunter1997cloningexpressionand pages 6-7, hunter1997cloningexpressionand pages 5-6) |
| Specific activity | 2516 units/mg protein when expressed in E. coli | (hunter1997cloningexpressionand pages 6-7) |
| Subcellular localization | Mitochondrial, specifically consistent with the mitochondrial matrix | (hunter1997cloningexpressionand pages 1-1, raamsdonk2009deletionofthe pages 2-3) |
| N-terminal transit peptide | Contains an N-terminal mitochondrial transit peptide; mature enzyme generated after targeting/processing | (hunter1997cloningexpressionand pages 1-1, hunter1997cloningexpressionand pages 4-5) |
| Physical mitochondrial association | Reported as physically associated with the I:III:IV respiratory supercomplex in the inner mitochondrial membrane context | (braeckman2016invivodetection pages 2-3) |
| Isoelectric point (pI) | 6.5 | (hunter1997cloningexpressionand pages 6-7) |
| Chromosome location | Chromosome I | (hunter1997cloningexpressionand pages 1-1) |
| Key domains / family | Member of the iron/manganese superoxide dismutase family; Mn/Fe SOD-type enzyme | (hunter1997cloningexpressionand pages 6-7, hunter1997cloningexpressionand pages 1-1) |
| Inhibitor sensitivity | Not inhibited by hydrogen peroxide or potassium cyanide, consistent with MnSOD rather than Cu/ZnSOD | (hunter1997cloningexpressionand pages 6-7, hunter1997cloningexpressionand pages 1-1) |
| Functional complementation | Expressed SOD-2 protects SOD-deficient E. coli from methyl viologen-induced oxidative stress | (hunter1997cloningexpressionand pages 1-1) |
| Core biological role in worm | Major mitochondrial superoxide detox enzyme; also shapes redox signaling by controlling conversion of mitochondrial superoxide into signaling-competent peroxide | (raamsdonk2009deletionofthe pages 2-3, branicky2022stimulationofrasdependent pages 2-3, onukwufor2022areversiblemitochondrial pages 8-9) |
| Lifespan phenotype of loss | Deletion of sod-2 extends lifespan in C. elegans despite increased oxidative stress sensitivity and oxidative damage | (raamsdonk2009deletionofthe pages 1-2, raamsdonk2009deletionofthe pages 6-8, raamsdonk2009deletionofthe pages 3-5) |
| Mitochondrial-function phenotype of loss | sod-2 mutants show decreased oxygen consumption, slow development, low brood size, and slow defecation, resembling long-lived mitochondrial mutants | (raamsdonk2009deletionofthe pages 1-2, raamsdonk2009deletionofthe pages 9-10, raamsdonk2009deletionofthe pages 5-6) |
| Interaction with mitochondrial mutants | Extends lifespan in clk-1, but shortens lifespan in isp-1 backgrounds; supports a mitochondrial threshold model | (raamsdonk2009deletionofthe pages 8-9, raamsdonk2009deletionofthe pages 10-11, raamsdonk2009deletionofthe pages 9-10) |
| Role in ROS signaling | Loss of SOD-2 elevates mitochondrial superoxide; longevity signaling requires downstream conversion involving SOD-1 and LET-60/RAS redox signaling | (branicky2022stimulationofrasdependent pages 2-3, raamsdonk2009deletionofthe pages 5-6) |
| Role in reproduction | SOD-2-generated H2O2 activates sperm pseudopod extension and is required for normal sperm activation | (sakamoto2017hydrogenperoxideproduced pages 10-11, sakamoto2017hydrogenperoxideproduced pages 1-2) |
| Comparison with SOD-3: localization/class | Both SOD-2 and SOD-3 are mitochondrial MnSODs with transit peptides and comparable specific activities | (hunter1997cloningexpressionand pages 1-1, hunter1997cloningexpressionand pages 4-5) |
| Comparison with SOD-3: biochemical differences | Both are dimers and active MnSODs, but show different electrophoretic mobilities and isoelectric points | (hunter1997cloningexpressionand pages 1-1) |
| Comparison with SOD-3: expression/regulation | sod-2 is relatively constitutive and similar in adult/dauer, whereas sod-3 is more dauer-associated and strongly induced in daf-2 mutants; sod-2 is more linked to SKN-1/p38 MAPK regulation, sod-3 to DAF-16/IIS | (honda1999thedafβ2gene pages 6-7, yanase2020interactionbetweenthe pages 4-5, honda1999thedafβ2gene pages 3-5) |
Table: This table summarizes the main biochemical, localization, and functional properties of C. elegans SOD-2, including direct comparisons with the paralog SOD-3. It is useful as a compact reference for annotation of sod-2/MnSOD in mitochondrial redox biology and lifespan signaling.
SOD-2 catalyzes the dismutation of the superoxide radical anion (Oββ’β») into hydrogen peroxide (HβOβ) and molecular oxygen (Oβ), using a manganese cofactor at its active site (hunter1997cloningexpressionand pages 1-1, hunter1997cloningexpressionand pages 1-2). The reaction is:
2 Oββ’β» + 2 HβΊ β HβOβ + Oβ
Recombinant SOD-2 expressed in E. coli deficient in endogenous SODs exhibits a specific activity of 2,516 units/mg protein, comparable to that of its paralog SOD-3 (hunter1997cloningexpressionand pages 6-7). The mature SOD-2 monomer has a calculated molecular mass of 21,986 Da (192 amino acids) and functions as an active homodimer with a measured dimer mass of 44,961 Da (hunter1997cloningexpressionand pages 6-7, hunter1997cloningexpressionand pages 5-6). Consistent with its identity as an MnSOD, SOD-2 is not inhibited by hydrogen peroxide or potassium cyanide, distinguishing it biochemically from the Cu/Zn class of superoxide dismutases (hunter1997cloningexpressionand pages 6-7, hunter1997cloningexpressionand pages 1-1). Both recombinant SOD-2 and SOD-3 conferred comparable protection against methyl viologen (paraquat)-induced oxidative stress when expressed in SOD-deficient E. coli (hunter1997cloningexpressionand pages 1-1).
A critical insight from recent work is that the product of the SOD-2 catalyzed reactionβHβOββis not merely a detoxified by-product but serves as a biologically active signaling molecule in multiple physiological contexts (sakamoto2017hydrogenperoxideproduced pages 10-11, branicky2022stimulationofrasdependent pages 2-3).
SOD-2 contains an N-terminal mitochondrial transit peptide that targets the protein to the mitochondrial matrix, where the transit peptide is cleaved to generate the mature enzyme (hunter1997cloningexpressionand pages 1-1, hunter1997cloningexpressionand pages 4-5). The positively charged residues in the transit peptide and at the beginning of the mature peptide are characteristic of mitochondrially targeted MnSODs across species (hunter1997cloningexpressionand pages 4-5). Within the mitochondria, SOD-2 has been reported to be physically associated with the I:III:IV respiratory supercomplex of the inner mitochondrial membrane (braeckman2016invivodetection pages 2-3), placing it in close proximity to the major sites of superoxide generationβparticularly Complex I and Complex III of the electron transport chain (raamsdonk2009deletionofthe pages 2-3). This localization is functionally significant, as the mitochondrial matrix is the primary intracellular compartment where superoxide is actively produced during oxidative phosphorylation (raamsdonk2009deletionofthe pages 2-3, honda1999thedafβ2gene pages 2-3).
SOD-2 is expressed under normal growth conditions in C. elegans, and its transcripts are trans-spliced to the SL-1 leader sequence, indicating mono-cistronic transcription (hunter1997cloningexpressionand pages 1-1, hunter1997cloningexpressionand pages 5-6). Northern blot analysis confirms a single transcript of approximately 800 nucleotides (hunter1997cloningexpressionand pages 5-6).
A key distinction between the two mitochondrial MnSODs involves their transcriptional regulation. sod-2 is expressed at relatively constitutive levels across developmental stages, including both adult and dauer stages, whereas sod-3 is more specifically induced during the dauer stage and in daf-2 (insulin receptor) mutants (honda1999thedafβ2gene pages 6-7, honda1999thedafβ2gene pages 3-5). Importantly, sod-2 mRNA levels in daf-2 mutants are comparable to wild-type, while sod-3 mRNA is markedly elevated (honda1999thedafβ2gene pages 3-5). This indicates that sod-2 and sod-3 are regulated through distinct transcriptional programs: sod-2 is predominantly regulated by the SKN-1/Nrf2 transcription factor acting downstream of the p38 MAPK signaling pathway, whereas sod-3 is primarily a target of DAF-16/FOXO within the insulin/IGF-1 signaling (IIS) pathway (yanase2020interactionbetweenthe pages 4-5). Although putative DAF-16 binding elements (DBEs) exist in the sod-2 promoter, functional studies in daf-16 null mutants suggest these sites are non-functional for sod-2 regulation (yanase2020interactionbetweenthe pages 4-5).
One of the most striking and paradigm-challenging findings regarding sod-2 is that its deletion extends lifespan in C. elegans, in stark contrast to yeast, flies, and mice where SOD2 loss shortens lifespan (raamsdonk2009deletionofthe pages 1-2, raamsdonk2009deletionofthe pages 2-3). Van Raamsdonk and Hekimi (2009) demonstrated that sod-2 deletion mutants live significantly longer than wild-type worms, despite exhibiting increased oxidative damage (measured as oxidatively modified proteins) and increased sensitivity to paraquat- and juglone-induced oxidative stress (raamsdonk2009deletionofthe pages 1-2, raamsdonk2009deletionofthe pages 3-5). This paradox fundamentally challenged the oxidative stress theory of aging.
The mechanism underlying this lifespan extension appears to involve altered mitochondrial function rather than changes in oxidative stress per se. sod-2 mutant worms display a suite of phenotypes characteristic of long-lived mitochondrial mutants: slow post-embryonic development, reduced brood size, slow defecation cycle rate, and critically, decreased whole-worm oxygen consumption (raamsdonk2009deletionofthe pages 1-2, raamsdonk2009deletionofthe pages 5-6, raamsdonk2009deletionofthe pages 6-8). Genetic interaction studies revealed that sod-2 deletion markedly extends lifespan (by ~15 days) in clk-1 mutant backgrounds (which have mildly impaired mitochondrial function), but decreases lifespan (by ~25 days) in isp-1 mutant backgrounds (which already have >50% reduced respiration) (raamsdonk2009deletionofthe pages 8-9, raamsdonk2009deletionofthe pages 9-10, raamsdonk2009deletionofthe pages 6-8). This led to a mitochondrial threshold model: moderate reductions in mitochondrial function can activate compensatory longevity-promoting programs, but when dysfunction exceeds a critical threshold, the organism can no longer compensate and lifespan shortens (raamsdonk2009deletionofthe pages 10-11, raamsdonk2009deletionofthe pages 9-10).
Recent work by Branicky et al. (2022) has elucidated a mechanistic pathway explaining how loss of SOD-2 extends lifespan through a RAS-dependent ROS signaling (RDRS) pathway. Loss of SOD-2 elevates mitochondrial superoxide levels. This superoxide exits the mitochondria and is converted to hydrogen peroxide by cytoplasmic SOD-1 (Cu/ZnSOD). The HβOβ then acts on a redox-sensitive cysteine residue (C118) of LET-60/RAS, modulating its activity and triggering a global program of gene expression that affects approximately half of the genome (branicky2022stimulationofrasdependent pages 2-3). Critically, the longevity benefit of sod-2 loss requires SOD-1: when SOD-1 is also deleted, the lifespan extension of sod-2 mutants is completely suppressed, demonstrating that the longevity signal is not from superoxide itself but from the SOD-1-generated HβOβ acting through cytoplasmic RAS signaling (branicky2022stimulationofrasdependent pages 2-3).
Onukwufor et al. (2022) demonstrated that SOD-2 is required for Complex I-derived ROS to drive behavioral responses in C. elegans. Using optogenetic tools to generate site-specific mitochondrial ROS, they showed that SOD-2/SOD-3-dependent conversion of superoxide to HβOβ is necessary for ROS-induced locomotory remodeling, specifically hypoxic avoidance behavior. In the absence of SOD-2, the behavioral response to Complex I ROS is abolished, though it can be rescued by a SOD mimetic compound (MnPyP) (onukwufor2022areversiblemitochondrial pages 8-9, onukwufor2022areversiblemitochondrial pages 6-8). This establishes SOD-2 as a critical mediator linking mitochondrial ROS production to acute behavioral outputs.
Senchuk et al. (2018) showed that elevated ROS in sod-2 mutants contributes to DAF-16/FOXO activation, which is required for the full longevity of long-lived mitochondrial mutants. The transcriptional changes in mitochondrial mutants overlap significantly with those in long-lived daf-2 (insulin/IGF-1 receptor) mutants, and DAF-16 along with multiple DAF-16-interacting proteins are required for full lifespan extension (prasad2013evaluationofrole pages 3-4). Overexpression of SOD-2 has also been shown to extend lifespan in a daf-16-dependent manner, indicating that both gain and loss of SOD-2 function can modulate longevity signaling through DAF-16, albeit through distinct mechanisms (prasad2013evaluationofrole pages 3-4).
Sakamoto and Imai (2017) discovered a surprising role for SOD-2 in sperm activation in C. elegans. The HβOβ produced by SOD-2's catalytic activity acts as a positive signaling molecule required for pseudopod extension during sperm activation. In sod-1;sod-2 double mutant sperm, pseudopod extension is defective, leading to significantly reduced brood size (sakamoto2017hydrogenperoxideproduced pages 10-11, sakamoto2017hydrogenperoxideproduced pages 1-2). Exogenous application of HβOβ rescues the activation defects of double mutant sperm, while the HβOβ scavenger ebselen completely inhibits pseudopod extension in wild-type sperm (sakamoto2017hydrogenperoxideproduced pages 10-11). Analysis of single mutants demonstrated that sod-2, rather than sod-1, is the specific SOD gene required for proper pseudopod extension during sperm activation (sakamoto2017hydrogenperoxideproduced pages 10-11, sakamoto2017hydrogenperoxideproduced pages 1-2).
SOD-2 plays a critical protective role in contexts of compromised mitochondrial morphology. Kanazawa et al. (2008) demonstrated that eat-3 mutants (defective in mitochondrial inner membrane fusion, homologous to human OPA1) are highly sensitive to loss of sod-2. The eat-3 mutants upregulate SOD-2 protein levels more than two-fold as a compensatory response, and depletion of sod-2 by RNAi or genetic mutation causes a strong negative effect on survival and growth in the eat-3 background (kanazawa2008thec.elegans pages 8-9, kanazawa2008thec.elegans pages 1-2). This effect is specific to sod-2, as loss of other SOD genes (sod-1, sod-3, sod-5) has only modest effects in eat-3 animals (kanazawa2008thec.elegans pages 9-10). The selective dependency on SOD-2 is consistent with its mitochondrial matrix localization, where disrupted cristae morphology in eat-3 mutants leads to increased free radical production that must be managed locally (kanazawa2008thec.elegans pages 9-10).
The following table summarizes the key pathways in which SOD-2 participates:
| Pathway | Key components | Role of SOD-2 | Biological outcome | Evidence |
|---|---|---|---|---|
| Mitochondrial superoxide detoxification | Mitochondrial electron transport chain; superoxide (O2β’β); Mn cofactor; SOD-2 in mitochondrial matrix; H2O2/O2 products | Primary mitochondrial Mn-superoxide dismutase that converts superoxide to hydrogen peroxide and oxygen; active dimeric enzyme with mitochondrial transit peptide and matrix localization | Limits mitochondrial superoxide burden and contributes to basal antioxidant defense; loss increases oxidative stress sensitivity and oxidative damage even when lifespan is not shortened | (hunter1997cloningexpressionand pages 6-7, hunter1997cloningexpressionand pages 1-1, raamsdonk2009deletionofthe pages 2-3, raamsdonk2009deletionofthe pages 3-5) |
| RAS-dependent ROS signaling (RDRS) | Mitochondrial superoxide; SOD-2; cytosolic SOD-1; H2O2; LET-60/RAS C118 redox switch | Loss of SOD-2 raises mitochondrial superoxide; longevity signal requires downstream conversion by SOD-1 to H2O2, which oxidizes LET-60/RAS and activates RDRS | Global transcriptional remodeling and lifespan extension from mitochondrial ROS signaling rather than simple detoxification | (branicky2022stimulationofrasdependent pages 2-3, raamsdonk2009deletionofthe pages 5-6) |
| p38 MAPK/SKN-1/Nrf2 regulation of sod-2 | p38 MAPK pathway; SKN-1/Nrf2; sod-2 promoter | sod-2 is regulated predominantly by SKN-1 rather than DAF-16 under stress-responsive conditions, especially in molecular compensation among sod mutants | Supports stress adaptation and longevity-associated redox homeostasis under intracellular oxidative stress | (yanase2020interactionbetweenthe pages 4-5) |
| Insulin/IGF-1 signaling (IIS) via DAF-2/DAF-16 | DAF-2 insulin/IGF-1 receptor; DAF-16/FoxO; MnSOD genes sod-2 and sod-3 | sod-2 is part of the MnSOD antioxidant network linked to longevity signaling, but unlike sod-3 it is not strongly induced in daf-2 mutants and appears less directly controlled by DAF-16 | Contributes to oxidative stress resistance framework of IIS, while sod-3 is the more prominent dauer/DAF-16-responsive MnSOD output | (honda1999thedafβ2gene pages 2-3, honda1999thedafβ2gene pages 6-7, honda1999thedafβ2gene pages 3-5) |
| Mitochondrial unfolded protein response (UPRmt) / mitochondrial dysfunction programs | Mitochondrial stress; mitochondrial proteostasis pathways; respiratory dysfunction; stress-response genes including SOD enzymes | SOD-2 is repeatedly discussed as part of mitochondrial stress-response programs and as a mitochondrial redox effector whose loss phenocopies long-lived mitochondrial mutants with reduced respiration | Links mitochondrial dysfunction to compensatory stress programs and altered lifespan trajectories | (raamsdonk2009deletionofthe pages 1-2, raamsdonk2009deletionofthe pages 5-6) |
| Complex I ROS signaling and hypoxic avoidance behavior | Complex I-derived ROS; SOD-2/SOD-3; H2O2; redox-sensitive thiol switch on NDUF-2.1-related pathway; locomotory/hypoxia avoidance circuitry | SOD-2 is required to convert complex I-derived superoxide into H2O2 that mediates behavioral signaling; loss of sod-2 abolishes ROS-triggered avoidance/photolocomotory responses | Enables mitochondrial ROS to function as a signal for hypoxic avoidance and acute behavioral adaptation | (onukwufor2022areversiblemitochondrial pages 8-9, onukwufor2022areversiblemitochondrial pages 6-8) |
| Sperm activation via H2O2 signaling | SOD-2; SOD-1; H2O2; Pronase-responsive sperm activation; pseudopod extension machinery | SOD-2-generated H2O2 acts as a positive signaling molecule required for sperm activation and pseudopod extension; exogenous H2O2 rescues activation defects in sod-1;sod-2 mutants | Promotes normal sperm motility/activation and supports fertility/brood size | (sakamoto2017hydrogenperoxideproduced pages 10-11, sakamoto2017hydrogenperoxideproduced pages 1-2, sakamoto2017hydrogenperoxideproduced pages 8-10) |
Table: This table summarizes the main signaling and biochemical pathways involving C. elegans SOD-2, emphasizing where it acts as a detoxifying enzyme versus a redox-signaling mediator. It is useful for functional annotation because it connects SOD-2 to localization, pathway context, and experimentally observed organismal outcomes.
C. elegans SOD-2 is a mitochondrial matrix-localized manganese superoxide dismutase that catalyzes the dismutation of superoxide radicals to hydrogen peroxide and oxygen. Beyond its canonical antioxidant function, SOD-2 has emerged as a critical node in mitochondrial redox signaling. Its enzymatic product, HβOβ, serves as a signaling molecule in at least three distinct biological contexts: (1) RAS-dependent longevity signaling, where mitochondrial superoxide escaping from the matrix is converted to cytoplasmic HβOβ by SOD-1 to activate LET-60/RAS (branicky2022stimulationofrasdependent pages 2-3); (2) sperm activation, where SOD-2-derived HβOβ directly drives pseudopod extension (sakamoto2017hydrogenperoxideproduced pages 10-11, sakamoto2017hydrogenperoxideproduced pages 1-2); and (3) behavioral responses, where SOD-2-dependent HβOβ production mediates Complex I ROS-triggered locomotory adaptation (onukwufor2022areversiblemitochondrial pages 8-9, onukwufor2022areversiblemitochondrial pages 6-8). The paradoxical lifespan extension upon sod-2 deletion reflects altered mitochondrial function and activation of compensatory longevity programs, rather than a simple reduction in oxidative damage (raamsdonk2009deletionofthe pages 1-2, raamsdonk2009deletionofthe pages 5-6). Transcriptionally, sod-2 is regulated predominantly by the SKN-1/Nrf2 pathway through p38 MAPK signaling, distinguishing it from its paralog sod-3, which is a primary target of DAF-16/FOXO in the insulin/IGF-1 signaling pathway (yanase2020interactionbetweenthe pages 4-5). Together, these findings position SOD-2 as both a protective antioxidant enzyme and a redox-signaling mediator at the interface of mitochondrial function, aging, reproduction, and behavior.
References
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(hunter1997cloningexpressionand pages 4-5): Thérèse Hunter, William H. Bannister, and Gary J. Hunter. Cloning, expression, and characterization of two manganese superoxide dismutases from caenorhabditis elegans *. The Journal of Biological Chemistry, 272:28652-28659, Nov 1997. URL: https://doi.org/10.1074/jbc.272.45.28652, doi:10.1074/jbc.272.45.28652. This article has 183 citations.
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(hunter1997cloningexpressionand pages 1-2): Thérèse Hunter, William H. Bannister, and Gary J. Hunter. Cloning, expression, and characterization of two manganese superoxide dismutases from caenorhabditis elegans *. The Journal of Biological Chemistry, 272:28652-28659, Nov 1997. URL: https://doi.org/10.1074/jbc.272.45.28652, doi:10.1074/jbc.272.45.28652. This article has 183 citations.
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(branicky2022stimulationofrasdependent pages 2-3): Robyn Branicky, Ying Wang, Arman Khaki, Ju-Ling Liu, Maximilian Kramer-Drauberg, and Siegfried Hekimi. Stimulation of ras-dependent ros signaling extends longevity by modulating a developmental program of global gene expression. Dec 2022. URL: https://doi.org/10.1126/sciadv.adc9851, doi:10.1126/sciadv.adc9851. This article has 17 citations and is from a highest quality peer-reviewed journal.
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(onukwufor2022areversiblemitochondrial pages 8-9): John O. Onukwufor, M. Arsalan Farooqi, AneΕΎka VodiΔkovΓ‘, Shon A. Koren, Aksana Baldzizhar, Brandon J. Berry, Gisela Beutner, George A. Porter, Vsevolod Belousov, Alan Grossfield, and Andrew P. Wojtovich. A reversible mitochondrial complex i thiol switch mediates hypoxic avoidance behavior in c. elegans. Nature Communications, May 2022. URL: https://doi.org/10.1038/s41467-022-30169-y, doi:10.1038/s41467-022-30169-y. This article has 44 citations and is from a highest quality peer-reviewed journal.
(raamsdonk2009deletionofthe pages 1-2): Jeremy M. Van Raamsdonk and Siegfried Hekimi. Deletion of the mitochondrial superoxide dismutase sod-2 extends lifespan in caenorhabditis elegans. PLoS Genetics, 5:e1000361, Feb 2009. URL: https://doi.org/10.1371/journal.pgen.1000361, doi:10.1371/journal.pgen.1000361. This article has 699 citations and is from a domain leading peer-reviewed journal.
(raamsdonk2009deletionofthe pages 6-8): Jeremy M. Van Raamsdonk and Siegfried Hekimi. Deletion of the mitochondrial superoxide dismutase sod-2 extends lifespan in caenorhabditis elegans. PLoS Genetics, 5:e1000361, Feb 2009. URL: https://doi.org/10.1371/journal.pgen.1000361, doi:10.1371/journal.pgen.1000361. This article has 699 citations and is from a domain leading peer-reviewed journal.
(raamsdonk2009deletionofthe pages 3-5): Jeremy M. Van Raamsdonk and Siegfried Hekimi. Deletion of the mitochondrial superoxide dismutase sod-2 extends lifespan in caenorhabditis elegans. PLoS Genetics, 5:e1000361, Feb 2009. URL: https://doi.org/10.1371/journal.pgen.1000361, doi:10.1371/journal.pgen.1000361. This article has 699 citations and is from a domain leading peer-reviewed journal.
(raamsdonk2009deletionofthe pages 9-10): Jeremy M. Van Raamsdonk and Siegfried Hekimi. Deletion of the mitochondrial superoxide dismutase sod-2 extends lifespan in caenorhabditis elegans. PLoS Genetics, 5:e1000361, Feb 2009. URL: https://doi.org/10.1371/journal.pgen.1000361, doi:10.1371/journal.pgen.1000361. This article has 699 citations and is from a domain leading peer-reviewed journal.
(raamsdonk2009deletionofthe pages 5-6): Jeremy M. Van Raamsdonk and Siegfried Hekimi. Deletion of the mitochondrial superoxide dismutase sod-2 extends lifespan in caenorhabditis elegans. PLoS Genetics, 5:e1000361, Feb 2009. URL: https://doi.org/10.1371/journal.pgen.1000361, doi:10.1371/journal.pgen.1000361. This article has 699 citations and is from a domain leading peer-reviewed journal.
(raamsdonk2009deletionofthe pages 8-9): Jeremy M. Van Raamsdonk and Siegfried Hekimi. Deletion of the mitochondrial superoxide dismutase sod-2 extends lifespan in caenorhabditis elegans. PLoS Genetics, 5:e1000361, Feb 2009. URL: https://doi.org/10.1371/journal.pgen.1000361, doi:10.1371/journal.pgen.1000361. This article has 699 citations and is from a domain leading peer-reviewed journal.
(raamsdonk2009deletionofthe pages 10-11): Jeremy M. Van Raamsdonk and Siegfried Hekimi. Deletion of the mitochondrial superoxide dismutase sod-2 extends lifespan in caenorhabditis elegans. PLoS Genetics, 5:e1000361, Feb 2009. URL: https://doi.org/10.1371/journal.pgen.1000361, doi:10.1371/journal.pgen.1000361. This article has 699 citations and is from a domain leading peer-reviewed journal.
(honda1999thedafβ2gene pages 6-7): Yoko Honda and Shuji Honda. The dafβ2 gene network for longevity regulates oxidative stress resistance and mnβsuperoxide dismutase gene expression in caenorhabditis elegans. The FASEB Journal, 13:1385-1393, Aug 1999. URL: https://doi.org/10.1096/fasebj.13.11.1385, doi:10.1096/fasebj.13.11.1385. This article has 968 citations.
(yanase2020interactionbetweenthe pages 4-5): Sumino Yanase, Kayo Yasuda, and Naoaki Ishii. Interaction between the ins/igf-1 and p38 mapk signaling pathways in molecular compensation of sod genes and modulation related to intracellular ros levels in c. elegans. Sep 2020. URL: https://doi.org/10.1016/j.bbrep.2020.100796, doi:10.1016/j.bbrep.2020.100796. This article has 37 citations and is from a peer-reviewed journal.
(honda1999thedafβ2gene pages 3-5): Yoko Honda and Shuji Honda. The dafβ2 gene network for longevity regulates oxidative stress resistance and mnβsuperoxide dismutase gene expression in caenorhabditis elegans. The FASEB Journal, 13:1385-1393, Aug 1999. URL: https://doi.org/10.1096/fasebj.13.11.1385, doi:10.1096/fasebj.13.11.1385. This article has 968 citations.
(honda1999thedafβ2gene pages 2-3): Yoko Honda and Shuji Honda. The dafβ2 gene network for longevity regulates oxidative stress resistance and mnβsuperoxide dismutase gene expression in caenorhabditis elegans. The FASEB Journal, 13:1385-1393, Aug 1999. URL: https://doi.org/10.1096/fasebj.13.11.1385, doi:10.1096/fasebj.13.11.1385. This article has 968 citations.
(onukwufor2022areversiblemitochondrial pages 6-8): John O. Onukwufor, M. Arsalan Farooqi, AneΕΎka VodiΔkovΓ‘, Shon A. Koren, Aksana Baldzizhar, Brandon J. Berry, Gisela Beutner, George A. Porter, Vsevolod Belousov, Alan Grossfield, and Andrew P. Wojtovich. A reversible mitochondrial complex i thiol switch mediates hypoxic avoidance behavior in c. elegans. Nature Communications, May 2022. URL: https://doi.org/10.1038/s41467-022-30169-y, doi:10.1038/s41467-022-30169-y. This article has 44 citations and is from a highest quality peer-reviewed journal.
(prasad2013evaluationofrole pages 3-4): Kedar Prasad and Stephen Bondy. Evaluation of role of oxidative stress on aging in caenorhabditis elegans: a brief review. Current Aging Science, 6:215-219, Dec 2013. URL: https://doi.org/10.2174/18746098112059990031, doi:10.2174/18746098112059990031. This article has 13 citations.
(kanazawa2008thec.elegans pages 8-9): Takayuki Kanazawa, Mauro Zappaterra, Ayako Hasegawa, Ashley P Wright, Erin D Newman-Smith, Karolyn F Buttle, Kent L McDonald, Carmen Mannella, and Alex van der Bliek. The c. elegans opa1 homologue eat-3 is essential for resistance to free radicals. PLoS Genetics, 4:e39, Feb 2008. URL: https://doi.org/10.1371/journal.pgen.1000022, doi:10.1371/journal.pgen.1000022. This article has 198 citations and is from a domain leading peer-reviewed journal.
(kanazawa2008thec.elegans pages 1-2): Takayuki Kanazawa, Mauro Zappaterra, Ayako Hasegawa, Ashley P Wright, Erin D Newman-Smith, Karolyn F Buttle, Kent L McDonald, Carmen Mannella, and Alex van der Bliek. The c. elegans opa1 homologue eat-3 is essential for resistance to free radicals. PLoS Genetics, 4:e39, Feb 2008. URL: https://doi.org/10.1371/journal.pgen.1000022, doi:10.1371/journal.pgen.1000022. This article has 198 citations and is from a domain leading peer-reviewed journal.
(kanazawa2008thec.elegans pages 9-10): Takayuki Kanazawa, Mauro Zappaterra, Ayako Hasegawa, Ashley P Wright, Erin D Newman-Smith, Karolyn F Buttle, Kent L McDonald, Carmen Mannella, and Alex van der Bliek. The c. elegans opa1 homologue eat-3 is essential for resistance to free radicals. PLoS Genetics, 4:e39, Feb 2008. URL: https://doi.org/10.1371/journal.pgen.1000022, doi:10.1371/journal.pgen.1000022. This article has 198 citations and is from a domain leading peer-reviewed journal.
(sakamoto2017hydrogenperoxideproduced pages 8-10): Taro Sakamoto and Hirotaka Imai. Hydrogen peroxide produced by superoxide dismutase sod-2 activates sperm in caenorhabditis elegans. Journal of Biological Chemistry, 292:14804-14813, Sep 2017. URL: https://doi.org/10.1074/jbc.m117.788901, doi:10.1074/jbc.m117.788901. This article has 105 citations and is from a domain leading peer-reviewed journal.
UniProt: P31161 (SODM1_CAEEL). Gene: sod-2; synonym sdm-1; ORF F10D11.1;
WormBase WBGene00004931. Chromosome I. 221 aa precursor (24-aa mitochondrial
transit peptide, mature chain 25-221). EC 1.15.1.1. PDB: 3DC6 (1.80 Γ
).
This is the primary/constitutive mitochondrial manganese superoxide dismutase
(MnSOD) of C. elegans. It is one of two mitochondrial MnSODs β the paralog
sod-3 is on chromosome X and is the DAF-16/insulin-signalling-INDUCIBLE
mtSOD normally expressed at very low basal levels. The two proteins are ~86%
identical, so evidence must be attributed carefully (see paralog section below).
C. elegans has five SOD genes total: sod-1 (major cytosolic Cu/Zn), sod-2 and
sod-3 (mitochondrial MnSOD), sod-4 (extracellular Cu/Zn), sod-5 (cytosolic
Cu/Zn).
Additional sod-2-specific literature retrieved (PMIDs then cached and cited in the
review):
- Lifespan extension (seminal). Van Raamsdonk & Hekimi 2009 deleted each of the
five worm sod genes; none shortens lifespan and sod-2 loss extends it
[PMID:19197346 "we find that sod-2 mutants are long-lived despite a significant
increase in oxidatively damaged proteins"; "deletion of sod-2 extends worm lifespan
by altering mitochondrial function"]. Threshold model: sod-2 deletion increases
lifespan in clk-1 (mild mito dysfunction) but decreases it in isp-1 (severe)
PMID:19197346.
- Mechanism (RDRS). Branicky et al. 2022 Sci Adv: loss of SOD-2 raises
mitochondrial superoxide; cytosolic SOD-1 converts it to H2O2 that oxidizes
LET-60/RAS Cys118, driving a genome-wide developmental program; requires SOD-1
PMID:36449615. This
substantially NARROWS knowledge gap 1 (mechanism of longevity).
- Sperm activation (sod-2-specific). Sakamoto & Imai 2017: SOD-2-produced H2O2 is
a positive signal for sperm pseudopod extension; sod-2, not sod-1, is the required
SOD [PMID:28724632 "sod-2 is required for pseudopod extension"; "SOD-2 plays an
important role in the sperm activation of C. elegans by producing H2O2 as an
activator of pseudopod extension"]. Reinforces sod-2/sod-3 non-redundancy and the
signalling (not merely detoxifying) role of the H2O2 product.
- Transcriptional regulation split (from falcon; sources not cached). falcon
reports sod-2 is regulated mainly by SKN-1/Nrf2 via p38 MAPK, whereas sod-3 is a
DAF-16/FOXO (insulin/IGF-1) target (Yanase 2020; Honda 1999). Not independently
quote-verified here (papers not in cache); recorded as context only.
id: P31161
gene_symbol: sod-2
product_type: PROTEIN
status: COMPLETE
taxon:
id: NCBITaxon:6239
label: Caenorhabditis elegans
description: >-
sod-2 encodes the principal manganese-dependent superoxide dismutase (MnSOD) of
the Caenorhabditis elegans mitochondrion. The nuclear-encoded precursor carries
an N-terminal mitochondrial transit peptide that directs import into the
mitochondrial matrix, where the mature chain assembles into the characteristic
iron/manganese superoxide dismutase fold and binds one catalytic Mn(2+) ion per
subunit. The enzyme dismutates the superoxide anion radical, a by-product of the
respiratory electron transport chain, into hydrogen peroxide and molecular oxygen
(2 superoxide + 2 H+ -> H2O2 + O2; EC 1.15.1.1), providing a first line of
antioxidant defense within the organelle. C. elegans has a second, closely
related mitochondrial MnSOD, sod-3 (~86% identical), which is expressed at low
basal levels and is strongly induced by the DAF-16/FOXO branch of insulin/IGF-1
signalling; sod-2 is the constitutively expressed and quantitatively dominant
mitochondrial isoform. Beyond bulk matrix scavenging, SOD-2 physically associates
with the respiratory-chain supercomplex I:III:IV, positioning it to detoxify
superoxide at its site of production and potentially to influence supercomplex
stability and complex I/II activity. Counterintuitively for a core antioxidant
enzyme, loss of sod-2 does not shorten and in several mitochondrial-mutant
backgrounds can extend C. elegans lifespan, a finding central to debates over the
role of reactive oxygen species in aging. The enzyme's hydrogen peroxide product
also serves as a signalling molecule: it contributes to a RAS-dependent
ROS-signalling program linked to longevity and is required for sperm pseudopod
extension during sperm activation.
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: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:0000117
title: Electronic Gene Ontology annotations created by ARBA machine learning models
findings: []
- id: GO_REF:0000120
title: Combined Automated Annotation using Multiple IEA Methods
findings: []
- id: PMID:19197346
title: Deletion of the mitochondrial superoxide dismutase sod-2 extends lifespan
in Caenorhabditis elegans.
findings:
- statement: >-
Seminal demonstration that deleting the primary mitochondrial MnSOD sod-2
extends C. elegans lifespan despite increased protein oxidative damage and
heightened sensitivity to oxidative stress, directly challenging the
oxidative-damage theory of aging. sod-2 mutants phenocopy long-lived
mitochondrial mutants (slow development, small brood, reduced respiration).
reference_review:
relevance: HIGH
correctness: VERIFIED
review_notes: >-
PubMed-verified (PMID 19197346, PMC2628729) via DOI 10.1371/journal.pgen.1000361.
The defining reference for the counterintuitive longevity phenotype of sod-2
loss.
- id: PMID:28724632
title: Hydrogen peroxide produced by superoxide dismutase SOD-2 activates sperm
in Caenorhabditis elegans.
findings:
- statement: >-
SOD-2-generated hydrogen peroxide acts as a positive signaling molecule
required for sperm pseudopod extension during activation; sod-2 (not sod-1)
is the specific SOD required, linking SOD-2 enzymatic output to fertility.
reference_review:
relevance: MEDIUM
correctness: VERIFIED
review_notes: >-
PubMed-verified (PMID 28724632, PMC5592662) via DOI 10.1074/jbc.M117.788901.
Establishes a signalling (H2O2-mediated) role for SOD-2 output distinct from
bulk detoxification.
- id: PMID:36449615
title: Stimulation of RAS-dependent ROS signaling extends longevity by modulating
a developmental program of global gene expression.
findings:
- statement: >-
Proposes the RAS-dependent ROS signaling (RDRS) mechanism for sod-2 longevity:
loss of SOD-2 raises mitochondrial superoxide, which is converted by cytosolic
SOD-1 to hydrogen peroxide that oxidizes a redox-sensitive cysteine of
LET-60/RAS, driving a global developmental gene-expression program; the
lifespan extension requires SOD-1.
reference_review:
relevance: HIGH
correctness: VERIFIED
review_notes: >-
PubMed-verified (PMID 36449615, PMC9710873) via DOI 10.1126/sciadv.adc9851.
Provides a mechanistic account that narrows the long-standing gap in how sod-2
loss extends lifespan.
- id: PMID:20188671
title: The matrix peptide exporter HAF-1 signals a mitochondrial UPR by activating
the transcription factor ZC376.7 in C. elegans.
findings:
- statement: >-
High-throughput direct-assay (mass-spectrometry) source underlying the GOA
mitochondrion localization annotation for SOD-2. The cached abstract concerns
HAF-1/ClpP-mediated mitochondrial unfolded protein response signalling and
does not itself discuss sod-2; the annotation reflects detection of SOD-2 in
a mitochondrial proteome dataset.
reference_review:
relevance: LOW
correctness: VERIFIED
review_notes: >-
PMID resolves to the correct Haynes et al. 2010 Mol Cell paper on the
mitochondrial UPR. It is the assigned source of an HDA mitochondrial
localization for SOD-2; the abstract does not mention sod-2 (full text /
proteomics supplement not in cache), so no sod-2-specific verbatim quote is
available. Mitochondrial localization of a MnSOD is biologically unambiguous.
- id: PMID:23895727
title: Novel interactions between mitochondrial superoxide dismutases and the electron
transport chain.
findings:
- statement: >-
SOD-2 is the primary mitochondrial superoxide dismutase and co-localizes by
blue-native gel with the respiratory supercomplex I:III:IV; loss of SOD-2
specifically lowers complex I and II activity and destabilizes supercomplex
formation. sod-2 single mutants have a normal lifespan, but loss of sod-2 can
extend the lifespan of some electron-transport-chain mutants.
reference_review:
relevance: HIGH
correctness: VERIFIED
review_notes: >-
Full text cached (PMC3838459). The richest sod-2-specific source: directly
supports the supercomplex association (Fig 4D), the primary-mtSOD identity,
and the counterintuitive lifespan phenotypes. An anti-SOD-2 antibody with
partial cross-reactivity to SOD-3 is noted by the authors, but the
sod-2-specific band is lost in the sod-2 mutant, so the SOD-2 localization is
real.
- id: PMID:9353332
title: Cloning, expression, and characterization of two manganese superoxide dismutases
from Caenorhabditis elegans.
findings:
- statement: >-
Cloned sod-2 and sod-3, showed both encode mitochondrial (transit-peptide
bearing) manganese-type superoxide dismutases, and directly measured their
enzymatic activity after heterologous expression in SOD-deficient E. coli
(Mn-type: insensitive to hydrogen peroxide and cyanide; dimeric; protective
against paraquat/methyl-viologen oxidative stress).
reference_review:
relevance: HIGH
correctness: VERIFIED
review_notes: >-
Abstract-only in cache (full_text_available: false), but the abstract
explicitly reports the direct biochemical characterization that underlies the
WormBase IDA (superoxide dismutase activity) and IMP (removal of superoxide
radicals) annotations. Note the IMP is based on heterologous E. coli
complementation, not a worm-mutant phenotype.
existing_annotations:
- term:
id: GO:0005739
label: mitochondrion
evidence_type: IBA
original_reference_id: GO_REF:0000033
qualifier: is_active_in
review:
summary: >-
Phylogenetic (IBA) inference that SOD-2 is active in the mitochondrion.
Correct but less specific than the mitochondrial matrix, which is where this
MnSOD acts.
action: KEEP_AS_NON_CORE
reason: >-
Consistent with the mitochondrial transit peptide and with experimental
localization, but generic relative to mitochondrial matrix (GO:0005759),
which is retained as the core location. Kept as a correct, less-specific
companion term.
- term:
id: GO:0004784
label: superoxide dismutase activity
evidence_type: IBA
original_reference_id: GO_REF:0000033
qualifier: enables
review:
summary: >-
Phylogenetic (IBA) inference of superoxide dismutase activity. This is the
core molecular function of SOD-2 and is directly confirmed experimentally.
action: ACCEPT
reason: >-
SOD-2 is an experimentally validated manganese superoxide dismutase; the IBA
call is fully concordant with the IDA evidence (PMID:9353332) and with the
Fe/Mn-SOD family assignment. Core function.
supported_by:
- reference_id: PMID:9353332
supporting_text: >-
The expressed enzymes, which were not inhibited by hydrogen peroxide or
cyanide, are dimeric, show quite different electrophoretic mobilities and
isoelectric points, but exhibit comparable specific activities.
- term:
id: GO:0030145
label: manganese ion binding
evidence_type: IBA
original_reference_id: GO_REF:0000033
qualifier: enables
review:
summary: >-
Phylogenetic (IBA) inference of manganese ion binding, the catalytic cofactor
of this MnSOD. Concordant with the UniProt Mn(2+) cofactor and Mn-ligand
residues, and with the enzyme's Mn-type biochemistry.
action: ACCEPT
reason: >-
Correct and specific metal-binding function: this is a Mn-type (not Fe- or
Cu/Zn-type) SOD, insensitive to hydrogen peroxide and cyanide, binding one
Mn(2+) per subunit. Core cofactor-binding function.
supported_by:
- reference_id: PMID:9353332
supporting_text: >-
The expressed enzymes, which were not inhibited by hydrogen peroxide or
cyanide, are dimeric, show quite different electrophoretic mobilities and
isoelectric points, but exhibit comparable specific activities.
- term:
id: GO:0004784
label: superoxide dismutase activity
evidence_type: IEA
original_reference_id: GO_REF:0000120
qualifier: enables
review:
summary: >-
Electronic (IEA) assignment of superoxide dismutase activity from combined
automated methods (ARBA/InterPro/EC/RHEA mapping). Redundant with the
experimental IDA and phylogenetic IBA calls for the same core function.
action: ACCEPT
reason: >-
Same core molecular function as the IDA/IBA annotations; the EC 1.15.1.1 /
RHEA:20696 mapping is correct for this enzyme. Retained as concordant
supporting evidence.
- term:
id: GO:0005759
label: mitochondrial matrix
evidence_type: IEA
original_reference_id: GO_REF:0000044
qualifier: located_in
review:
summary: >-
Electronic (SubCell) localization to the mitochondrial matrix, matching the
UniProt subcellular location and the N-terminal mitochondrial transit
peptide. This is the core site of SOD-2 action.
action: ACCEPT
reason: >-
Correct and appropriately specific localization for a matrix MnSOD; supported
by the transit peptide and by the primary-mtSOD role. Core location.
supported_by:
- reference_id: PMID:9353332
supporting_text: >-
Both deduced protein sequences contain the expected N-terminal
mitochondrial transit peptides.
- term:
id: GO:0006801
label: superoxide metabolic process
evidence_type: IEA
original_reference_id: GO_REF:0000002
qualifier: involved_in
review:
summary: >-
Electronic (InterPro2GO) assignment to the general superoxide metabolic
process. Correct but less specific than removal of superoxide radicals
(GO:0019430), which is the experimentally supported process.
action: KEEP_AS_NON_CORE
reason: >-
Accurate parent process, but subsumed by the more specific removal of
superoxide radicals term retained as core. Kept as a correct, less-informative
companion.
- term:
id: GO:0046872
label: metal ion binding
evidence_type: IEA
original_reference_id: GO_REF:0000002
qualifier: enables
review:
summary: >-
Electronic (InterPro2GO) generic metal-ion-binding annotation. Subsumed by
the specific manganese ion binding (GO:0030145) term.
action: KEEP_AS_NON_CORE
reason: >-
Correct but uninformative parent of manganese ion binding; the specific Mn(2+)
term is retained as core. Kept as a non-core, less-specific companion.
- term:
id: GO:0098803
label: respiratory chain complex
evidence_type: IEA
original_reference_id: GO_REF:0000117
qualifier: part_of
review:
summary: >-
Electronic (ARBA) assertion that SOD-2 is part_of the respiratory chain
complex. SOD-2 is a soluble matrix MnSOD that physically associates with
supercomplex I:III:IV (see the experimental located_in annotation), but it is
not a canonical structural subunit of an electron-transport complex, so the
part_of qualifier overstates the relationship.
action: KEEP_AS_NON_CORE
reason: >-
The experimentally supported relationship is association/co-localization with
the I:III:IV supercomplex (PMID:23895727, located_in), consistent with local
superoxide scavenging and possible supercomplex stabilization; SOD-2 does not
carry out or structurally constitute electron transport. The automated part_of
qualifier is an over-generalization, so this is retained only as a non-core
companion to the experimental located_in annotation rather than as evidence of
structural subunit membership.
supported_by:
- reference_id: PMID:23895727
supporting_text: >-
Western blots of BNGs indicated that SOD-2 co-localized with the I:III:IV
supercomplex (Figure 4D).
- term:
id: GO:0004784
label: superoxide dismutase activity
evidence_type: IDA
original_reference_id: PMID:9353332
qualifier: enables
review:
summary: >-
Direct assay (IDA) of superoxide dismutase activity: the mature SOD-2 protein
was expressed in SOD-deficient E. coli and shown to be an active, Mn-type
dismutase. This is the primary experimental evidence for the core function.
action: ACCEPT
reason: >-
Gold-standard experimental support for the defining molecular function.
Insensitivity to hydrogen peroxide and cyanide confirms the Mn-type (not Fe-
or Cu/Zn-type) mechanism. Core function.
supported_by:
- reference_id: PMID:9353332
supporting_text: >-
The expressed enzymes, which were not inhibited by hydrogen peroxide or
cyanide, are dimeric, show quite different electrophoretic mobilities and
isoelectric points, but exhibit comparable specific activities.
- reference_id: file:worm/sod-2/sod-2-deep-research-falcon.md
supporting_text: >-
Primary mitochondrial Mn-superoxide dismutase that converts superoxide to
hydrogen peroxide and oxygen
- term:
id: GO:0019430
label: removal of superoxide radicals
evidence_type: IMP
original_reference_id: PMID:9353332
qualifier: involved_in
review:
summary: >-
SOD-2 removes superoxide radicals: heterologous expression of the worm enzyme
rescued SOD-deficient E. coli from methyl-viologen (paraquat) oxidative
stress. This is the core biological process the enzyme serves.
action: ACCEPT
reason: >-
Functionally correct core process. The evidence is heterologous complementation
(protection of SOD-null E. coli against a superoxide generator) rather than a
worm loss-of-function phenotype, but it directly demonstrates superoxide-radical
removal by the SOD-2 protein. Core process.
supported_by:
- reference_id: PMID:9353332
supporting_text: >-
Both proteins were shown to be active in E. coli, providing similar
protection against methyl viologen-induced oxidative stress.
- term:
id: GO:0098803
label: respiratory chain complex
evidence_type: IDA
original_reference_id: PMID:23895727
qualifier: located_in
review:
summary: >-
Direct assay (IDA) showing SOD-2 co-localizes with mitochondrial supercomplex
I:III:IV by blue-native gel Western blotting. A genuine, sod-2-specific
localization finding, but a peripheral association rather than the enzyme's
core identity.
action: KEEP_AS_NON_CORE
reason: >-
Experimentally supported association of SOD-2 with the I:III:IV supercomplex,
consistent with local scavenging of superoxide at its site of production and a
possible supercomplex-stabilizing role. Retained with the located_in qualifier
as a real but non-core localization (SOD-2's core identity is a matrix MnSOD,
not a structural ETC subunit).
supported_by:
- reference_id: PMID:23895727
supporting_text: >-
Western blots of BNGs indicated that SOD-2 co-localized with the I:III:IV
supercomplex (Figure 4D).
- term:
id: GO:0005739
label: mitochondrion
evidence_type: HDA
original_reference_id: PMID:20188671
qualifier: located_in
review:
summary: >-
High-throughput direct-assay (HDA) mitochondrial-proteome localization of
SOD-2. Correct but generic relative to the mitochondrial matrix term.
action: KEEP_AS_NON_CORE
reason: >-
Mitochondrial localization of this MnSOD is biologically unambiguous and
concordant with the transit peptide and matrix localization; retained as a
correct, less-specific companion to mitochondrial matrix (GO:0005759). The
cited abstract concerns the mtUPR and does not mention sod-2, so no
sod-2-specific verbatim quote is available for the HDA dataset.
core_functions:
- description: >-
SOD-2 is a mitochondrial matrix manganese superoxide dismutase that catalyzes
the dismutation of the superoxide anion radical to hydrogen peroxide and
molecular oxygen (2 superoxide + 2 H+ -> H2O2 + O2; EC 1.15.1.1), the core
antioxidant defense of the mitochondrial matrix and the primary constitutively
expressed mtSOD of C. elegans.
molecular_function:
id: GO:0004784
label: superoxide dismutase activity
directly_involved_in:
- id: GO:0019430
label: removal of superoxide radicals
locations:
- id: GO:0005759
label: mitochondrial matrix
supported_by:
- reference_id: PMID:9353332
supporting_text: >-
The expressed enzymes, which were not inhibited by hydrogen peroxide or
cyanide, are dimeric, show quite different electrophoretic mobilities and
isoelectric points, but exhibit comparable specific activities.
- reference_id: PMID:9353332
supporting_text: >-
Both proteins were shown to be active in E. coli, providing similar
protection against methyl viologen-induced oxidative stress.
- description: >-
SOD-2 binds one catalytic manganese (Mn2+) ion per subunit, the redox-active
cofactor required for the dismutase mechanism. Its Mn-type identity is
established by insensitivity to hydrogen peroxide and cyanide, which inhibit
Fe-type and Cu/Zn-type SODs respectively.
molecular_function:
id: GO:0030145
label: manganese ion binding
locations:
- id: GO:0005759
label: mitochondrial matrix
supported_by:
- reference_id: PMID:9353332
supporting_text: >-
The expressed enzymes, which were not inhibited by hydrogen peroxide or
cyanide, are dimeric, show quite different electrophoretic mobilities and
isoelectric points, but exhibit comparable specific activities.
proposed_new_terms: []
suggested_questions:
- question: >-
By what mechanism does loss of the primary mitochondrial antioxidant SOD-2 fail
to shorten, and in some backgrounds extend, C. elegans lifespan β is superoxide
acting as a pro-longevity signal (mitohormesis), or is the effect mediated by
metabolic slowing and supercomplex remodeling?
- question: >-
What is the functional division of labour between the two nearly identical
mitochondrial MnSODs, SOD-2 (constitutive, dominant) and SOD-3 (DAF-16-inducible,
low basal), given their non-redundant and sometimes opposite genetic
interactions with electron-transport-chain mutants?
- question: >-
Is SOD-2's association with respiratory supercomplex I:III:IV purely a
positioning device for local superoxide scavenging, or does SOD-2 also act as a
structural stabilizer of the supercomplex independent of its catalytic activity?
suggested_experiments:
- description: >-
Catalytically-dead (metal-ligand mutant) versus wild-type sod-2 rescue in a
sod-2 null, scoring lifespan, complex I/II activity, and supercomplex formation,
to separate the scavenging function from a possible structural role.
- description: >-
Quantitative, isoform-resolved proteomics and tagged-allele localization of
SOD-2 versus SOD-3 across tissues and stress conditions to define their
non-redundant contributions and supercomplex occupancy.
- description: >-
Genetic-epistasis and redox-biosensor (e.g. mitochondrial roGFP/HyPer) analysis
of sod-2 loss in long-lived ETC mutants to test whether a superoxide/ROS signal,
rather than bulk oxidative damage, mediates the lifespan extension.
knowledge_gaps:
- gap_statement: >-
How loss of the primary mitochondrial superoxide dismutase SOD-2 extends
C. elegans lifespan is only partly resolved. A specific mechanism has been
proposed β a RAS-dependent ROS-signalling (RDRS) pathway in which elevated
mitochondrial superoxide is converted by cytosolic SOD-1 to hydrogen peroxide
that oxidizes a redox-sensitive cysteine of LET-60/RAS β but how much of the
longevity effect is attributable to this ROS signal versus to the concurrent
reduction in respiration, altered mitochondrial supercomplex stability, and
developmental/metabolic slowing remains undetermined, as does why the same loss
shortens lifespan once mitochondrial dysfunction exceeds a threshold.
boundary: >-
It is firmly established that SOD-2 is an active mitochondrial MnSOD and the
primary mitochondrial superoxide scavenger, that sod-2 single mutants are not
short-lived and are in fact long-lived despite increased protein oxidative
damage, that deletion of sod-2 markedly increases lifespan in clk-1 but
decreases it in isp-1 backgrounds, that loss of sod-2 lowers complex I/II
activity and supercomplex formation, and that a RDRS mechanism requiring SOD-1
can account for part of the extension. What is not established is the causal
weighting of the signalling versus metabolic contributions.
gap_kind:
- BIOLOGY
dark_aspect: BP_DARK
status: NARROWING
significance: >-
This is a central, counterintuitive case in the debate over the free-radical /
oxidative-damage theory of aging: a core antioxidant enzyme whose removal does
not shorten and can extend life. Resolving the causal weighting would clarify
when mitochondrial superoxide acts as a damaging agent versus a pro-longevity
signal.
provenance:
- reference_id: PMID:19197346
supporting_text: >-
we find that sod-2 mutants are long-lived despite a significant increase in
oxidatively damaged proteins
- reference_id: PMID:19197346
supporting_text: >-
deletion of sod-2 extends worm lifespan by altering mitochondrial function
- reference_id: PMID:36449615
supporting_text: >-
RDRS is regulated by negative feedback from the superoxide dismutase 1
(SOD-1)-dependent conversion of superoxide into cytoplasmic hydrogen peroxide,
which, in turn, acts on a redox-sensitive cysteine (C118) of RAS
- reference_id: PMID:23895727
supporting_text: >-
no single component of mitochondrial physiology that we studied correlates
simply with lifespan
- gap_statement: >-
The functional division of labour between the two nearly identical mitochondrial
manganese superoxide dismutases, SOD-2 and SOD-3, is undefined. It is unknown why
C. elegans maintains both, what distinguishes their substrates or sub-mitochondrial
contexts, and why loss of sod-2 versus sod-3 produces different (sometimes
opposite) genetic interactions with electron-transport-chain mutants.
boundary: >-
It is established that sod-2 and sod-3 are ~86% identical mitochondrial MnSODs,
that sod-2 is constitutively expressed and dominant while sod-3 is expressed at
low basal levels and induced by DAF-16/insulin signalling, that both associate
with supercomplex I:III:IV, and that they are functionally non-redundant (loss of
sod-2 versus sod-3 produces different genetic interactions with ETC mutants, and
sod-2 but not sod-1 is specifically required for H2O2-dependent sperm activation).
What is not established is the mechanistic basis of the non-redundancy at the
level of substrate, sub-mitochondrial context, or partner; the authors of the key
ETC study explicitly state that the sod-3/supercomplex relationship was still
under investigation.
gap_kind:
- BIOLOGY
dark_aspect: RESIDUAL_SUBGAP
status: OPEN
significance: >-
Two paralogous mitochondrial MnSODs with divergent, non-redundant phenotypes are
a clean model for how gene duplication partitions an antioxidant function; the
division of labour also determines which isoform is limiting under which stress.
provenance:
- reference_id: PMID:23895727
supporting_text: >-
Studies are now being undertaken to characterize the interaction of sod3 with
supercomplex I:III:IV formation
- reference_id: PMID:28724632
supporting_text: >-
sod-2 is required for pseudopod extension
- gap_statement: >-
Whether SOD-2's association with respiratory supercomplex I:III:IV reflects only
local superoxide scavenging at the site of ROS production, or whether SOD-2 also
acts as a direct structural stabilizer of the supercomplex independent of its
catalytic activity, is undetermined.
boundary: >-
It is established that SOD-2 co-localizes with the I:III:IV supercomplex by
blue-native gel and that sod-2 loss reduces supercomplex formation and complex I
activity. The open question is causality/mechanism: complex I function falls out
of proportion to the measured ROS damage, so a catalysis-independent structural
role remains possible but unproven.
gap_kind:
- BIOLOGY
dark_aspect: RESIDUAL_SUBGAP
status: OPEN
significance: >-
Distinguishing a scavenging role from a structural role would determine whether
MnSOD is a modular antioxidant or an integral stabilizer of the electron
transport chain, with implications for how supercomplex integrity is maintained.
provenance:
- reference_id: PMID:23895727
supporting_text: >-
it is also possible that the mtSODs may directly serve as stabilizing factors
in the I:III:IV supercomplex