Gsta4 encodes rat glutathione S-transferase alpha-4 (GSTA4-4), an alpha-class cytosolic GST that conjugates reduced glutathione to hydrophobic electrophiles. Among the alpha-class paralogs (Gsta1/2/3/4), Gsta4 is functionally distinguished by its high catalytic efficiency toward lipid peroxidation-derived alpha,beta-unsaturated aldehydes, especially 4-hydroxynonenal (4-HNE), which it detoxifies by GSH conjugation (Michael addition). The enzyme is a homodimer found mainly in the cytosol, with a stress-inducible mitochondrial pool that protects mitochondria from reactive lipid aldehydes. Its expression in rat brain, liver and other tissues is induced by toxicants and oxidative stress (e.g. nicotine, NNK, paraquat/zinc, lithium). Much of the detailed kinetic and loss-of-function evidence for GSTA4-4 comes from the human enzyme and mouse Gsta4-null models.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0004364 glutathione transferase activity | IBA GO_REF:0000033 | ACCEPT | Summary: Gsta4's glutathione conjugation of lipid peroxidation products and xenobiotic electrophiles supports retaining glutathione transferase activity as a direct annotation (IBA, GO_REF:0000033). Reason: glutathione transferase activity is a specific catalytic activity matching Gsta4's documented role in glutathione conjugation of lipid peroxidation products and xenobiotic electrophiles. Supporting Evidence: UniProtKB:P14942 Reaction=RX + glutathione = an S-substituted glutathione + a halide anion + H(+) UniProtKB:P14942 FUNCTION: Conjugation of reduced glutathione to a wide number of exogenous and endogenous hydrophobic electrophiles. file:rat/Gsta4/Gsta4-deep-research-falcon.md For 4-HNE and related substrates, GSTA4-4 forms glutathionylated adducts such as **GS-HNE/GS-NE**, supporting phase II detoxification and control of reactive aldehyde signaling. |
| GO:0006749 glutathione metabolic process | IBA GO_REF:0000033 | ACCEPT | Summary: Gsta4's glutathione conjugation of lipid peroxidation products and xenobiotic electrophiles supports retaining glutathione metabolic process as a direct annotation (IBA, GO_REF:0000033). Reason: glutathione metabolic process is a direct metabolic process expected from Gsta4's documented role in glutathione conjugation of lipid peroxidation products and xenobiotic electrophiles. Supporting Evidence: UniProtKB:P14942 Reaction=RX + glutathione = an S-substituted glutathione + a halide anion + H(+) UniProtKB:P14942 FUNCTION: Conjugation of reduced glutathione to a wide number of exogenous and endogenous hydrophobic electrophiles. file:rat/Gsta4/Gsta4-deep-research-falcon.md The best-supported biological role is **detoxification of reactive lipid aldehydes**, especially **4-HNE**, thereby limiting **protein carbonylation**, oxidative damage, and downstream stress signaling. |
| GO:0006805 xenobiotic metabolic process | IBA GO_REF:0000033 | ACCEPT | Summary: Gsta4's glutathione conjugation of lipid peroxidation products and xenobiotic electrophiles supports retaining xenobiotic metabolic process as a direct annotation (IBA, GO_REF:0000033). Reason: xenobiotic metabolic process is a direct metabolic process expected from Gsta4's documented role in glutathione conjugation of lipid peroxidation products and xenobiotic electrophiles. Supporting Evidence: UniProtKB:P14942 FUNCTION: Conjugation of reduced glutathione to a wide number of exogenous and endogenous hydrophobic electrophiles. UniProtKB:P14942 FUNCTION: Conjugation of reduced glutathione to a wide number of exogenous and endogenous hydrophobic electrophiles. |
| GO:0004364 glutathione transferase activity | IEA GO_REF:0000120 | ACCEPT | Summary: Gsta4's glutathione conjugation of lipid peroxidation products and xenobiotic electrophiles supports retaining glutathione transferase activity as a direct annotation (IEA, GO_REF:0000120). Reason: glutathione transferase activity is a specific catalytic activity matching Gsta4's documented role in glutathione conjugation of lipid peroxidation products and xenobiotic electrophiles. Supporting Evidence: UniProtKB:P14942 Reaction=RX + glutathione = an S-substituted glutathione + a halide anion + H(+) UniProtKB:P14942 FUNCTION: Conjugation of reduced glutathione to a wide number of exogenous and endogenous hydrophobic electrophiles. |
| GO:0005737 cytoplasm | IEA GO_REF:0000044 | KEEP AS NON CORE | Summary: cytoplasm is retained as useful context for Gsta4, but it is not the defining core function (IEA, GO_REF:0000044). Reason: cytoplasm records where Gsta4 has been observed, but localization does not define the gene product's primary activity. Supporting Evidence: UniProtKB:P14942 SUBCELLULAR LOCATION: Cytoplasm. file:rat/Gsta4/Gsta4-deep-research-falcon.md Although GSTs are classically described as **cytosolic**, GSTA4-4 has strong evidence for **mitochondrial association** |
| GO:0042802 identical protein binding | ISO GO_REF:0000121 | KEEP AS NON CORE | Summary: identical protein binding is retained as useful context for Gsta4, but it is not the defining core function (ISO, GO_REF:0000121). Reason: identical protein binding records substrate, cofactor, or quaternary-structure context for Gsta4, but the curated core function is glutathione conjugation of lipid peroxidation products and xenobiotic electrophiles. Supporting Evidence: UniProtKB:P14942 SUBUNIT: Homodimer. UniProtKB:P14942 SUBUNIT: Homodimer. |
| GO:0061771 response to caloric restriction | ISO GO_REF:0000121 | MARK AS OVER ANNOTATED | Summary: response to caloric restriction is treated as over-annotation because it reflects context or consequence rather than Gsta4's direct role (ISO, GO_REF:0000121). Reason: response to caloric restriction reflects exposure, expression, phenotype, or downstream pathway context rather than the direct Gsta4 role in glutathione conjugation of lipid peroxidation products and xenobiotic electrophiles. Propagation Review Root cause: PROPAGATION BAD Failure modes: CONTEXT OR TISSUE MISMATCH ROLE CONFLATION Sources checked: MGI:MGI:1309515 Β· mouse Gsta4 SUPPORTS SOURCE BUT NOT TARGET The mouse Gsta4 donor annotation records altered expression under caloric restriction; dietary regulation of the gene is not a glutathione-conjugation function of rat Gsta4. |
| GO:0005739 mitochondrion | ISO GO_REF:0000121 | KEEP AS NON CORE | Summary: mitochondrion is retained as useful context for Gsta4, but it is not the defining core function (ISO, GO_REF:0000121). Falcon deep research indicates mitochondrial association is stress-inducible (phosphorylation/Hsp70-dependent import) rather than incidental, supporting a genuine but secondary compartment for protecting mitochondria from reactive lipid aldehydes. Reason: mitochondrion records a functionally relevant but secondary compartment for Gsta4 (stress-inducible mitochondrial targeting), and localization does not define the gene product's primary activity. Note the detailed import-mechanism evidence (Ser189/Thr193 phosphorylation, Hsp70) derives from reviews of GSTA4-4 generally, not rat P14942 specifically. Supporting Evidence: PMID:9774145 Additionally, the brain mitochondrial matrix showed a markedly higher level of 4-hydroxynonenal specific GST activity and mGST A4-4 antibody-reactive protein than did the cytosolic fraction. file:rat/Gsta4/Gsta4-deep-research-falcon.md mitochondrial targeting can be activated by phosphorylation (e.g., **Ser189/Thr193**) and involves enhanced Hsp70 interaction, enabling import competence and increasing mitochondrial localization under oxidative/electrophilic stress (including 4-HNE exposure). |
| GO:0005829 cytosol | ISO GO_REF:0000121 | KEEP AS NON CORE | Summary: cytosol is retained as useful context for Gsta4, but it is not the defining core function (ISO, GO_REF:0000121). Reason: cytosol records where Gsta4 has been observed, but localization does not define the gene product's primary activity. Supporting Evidence: UniProtKB:P14942 SUBCELLULAR LOCATION: Cytoplasm. UniProtKB:P14942 SUBCELLULAR LOCATION: Cytoplasm. file:rat/Gsta4/Gsta4-deep-research-falcon.md Functionally, GSTA4-4 is best known as a **cytosolic** GST, but multiple studies also support **mitochondrial localization**. |
| GO:0015643 toxic substance binding | IPI PMID:11018474 Characterization of 4-hydroxy-2-nonenal metabolism in stella... | MARK AS OVER ANNOTATED | Summary: toxic substance binding is treated as over-annotation because the IPI evidence (4-HNE/CHEBI:58968) captures H-site substrate binding within the catalytic cycle rather than an independent non-catalytic binding activity (IPI, PMID:11018474). Reason: The 4-HNE interaction supporting this IPI annotation is the H-site substrate-binding step of the glutathione-conjugation catalytic cycle, which is already fully captured by the ACCEPTED GO:0004364 glutathione transferase activity. The falcon evidence ("GSH conjugation (Michael addition) catalyzed predominantly by GSTA4-4") supports catalysis, not a standalone binding function, so toxic substance binding is redundant over-annotation rather than a distinct activity. Supporting Evidence: PMID:11018474 The rate of 4-HNE metabolism attributable to glutathione S-transferase (GST) was similar in both cell lines, though differential cell specific expressions of GST isoforms GSTP1-1 and GSTA4-4 were observed. file:rat/Gsta4/Gsta4-deep-research-falcon.md A major cellular clearance pathway is **GSH conjugation (Michael addition)** catalyzed predominantly by **GSTA4-4**. |
| GO:0009635 response to herbicide | IEP PMID:20553223 Effect of zinc and paraquat co-exposure on neurodegeneration... | MARK AS OVER ANNOTATED | Summary: response to herbicide is treated as over-annotation because it reflects context or consequence rather than Gsta4's direct role (IEP, PMID:20553223). Reason: response to herbicide reflects exposure, expression, phenotype, or downstream pathway context rather than the direct Gsta4 role in glutathione conjugation of lipid peroxidation products and xenobiotic electrophiles. Supporting Evidence: PMID:20553223 Zn and/or PQ exposure increased gene expression of DAT, CYP2E1, GSTA4-4, MT-I and MT-II |
| GO:0010043 response to zinc ion | IEP PMID:20553223 Effect of zinc and paraquat co-exposure on neurodegeneration... | MARK AS OVER ANNOTATED | Summary: response to zinc ion is treated as over-annotation because it reflects context or consequence rather than Gsta4's direct role (IEP, PMID:20553223). Reason: response to zinc ion reflects exposure, expression, phenotype, or downstream pathway context rather than the direct Gsta4 role in glutathione conjugation of lipid peroxidation products and xenobiotic electrophiles. It derives from the same zinc/paraquat co-exposure expression experiment (PMID:20553223, IEP) as response to herbicide, with no mechanistic evidence that zinc directly modulates GSTA4-4 activity, so it is harmonized with response to herbicide as over-annotation. Supporting Evidence: PMID:20553223 Zn and/or PQ exposure increased gene expression of DAT, CYP2E1, GSTA4-4, MT-I and MT-II |
| GO:0035094 response to nicotine | IEP PMID:9774145 Preferential effects of nicotine and 4-(N-methyl-N-nitrosami... | MARK AS OVER ANNOTATED | Summary: response to nicotine is treated as over-annotation because it reflects context or consequence rather than Gsta4's direct role (IEP, PMID:9774145). Reason: response to nicotine reflects exposure, expression, phenotype, or downstream pathway context rather than the direct Gsta4 role in glutathione conjugation of lipid peroxidation products and xenobiotic electrophiles. Supporting Evidence: PMID:9774145 Both of these toxins induced the level of GST A4-4 mRNA in the brain, while they caused a marked reduction in the liver GST A4-4 mRNA pool. |
| GO:0071285 cellular response to lithium ion | IEP PMID:18082333 The effect of mood stabilizer lithium on expression and acti... | MARK AS OVER ANNOTATED | Summary: cellular response to lithium ion is treated as over-annotation because it reflects context or consequence rather than Gsta4's direct role (IEP, PMID:18082333). Reason: cellular response to lithium ion reflects exposure, expression, phenotype, or downstream pathway context rather than the direct Gsta4 role in glutathione conjugation of lipid peroxidation products and xenobiotic electrophiles. Supporting Evidence: PMID:18082333 chronic lithium treatment not only increased GST M1 mRNA levels, but also increased GST M3, M5 and A4 mRNA levels |
| GO:0006749 glutathione metabolic process | ISO GO_REF:0000121 | ACCEPT | Summary: Gsta4's glutathione conjugation of lipid peroxidation products and xenobiotic electrophiles supports retaining glutathione metabolic process as a direct annotation (ISO, GO_REF:0000121). Reason: glutathione metabolic process is a direct metabolic process expected from Gsta4's documented role in glutathione conjugation of lipid peroxidation products and xenobiotic electrophiles. Supporting Evidence: UniProtKB:P14942 Reaction=RX + glutathione = an S-substituted glutathione + a halide anion + H(+) UniProtKB:P14942 FUNCTION: Conjugation of reduced glutathione to a wide number of exogenous and endogenous hydrophobic electrophiles. |
| GO:0006805 xenobiotic metabolic process | ISO GO_REF:0000121 | ACCEPT | Summary: Gsta4's glutathione conjugation of lipid peroxidation products and xenobiotic electrophiles supports retaining xenobiotic metabolic process as a direct annotation (ISO, GO_REF:0000121). Reason: xenobiotic metabolic process is a direct metabolic process expected from Gsta4's documented role in glutathione conjugation of lipid peroxidation products and xenobiotic electrophiles. Supporting Evidence: UniProtKB:P14942 FUNCTION: Conjugation of reduced glutathione to a wide number of exogenous and endogenous hydrophobic electrophiles. UniProtKB:P14942 FUNCTION: Conjugation of reduced glutathione to a wide number of exogenous and endogenous hydrophobic electrophiles. |
| GO:0042803 protein homodimerization activity | ISO GO_REF:0000121 | KEEP AS NON CORE | Summary: protein homodimerization activity is retained as useful context for Gsta4, but it is not the defining core function (ISO, GO_REF:0000121). Reason: protein homodimerization activity records substrate, cofactor, or quaternary-structure context for Gsta4, but the curated core function is glutathione conjugation of lipid peroxidation products and xenobiotic electrophiles. Supporting Evidence: UniProtKB:P14942 SUBUNIT: Homodimer. UniProtKB:P14942 SUBUNIT: Homodimer. |
| GO:0004364 glutathione transferase activity | ISO GO_REF:0000121 | ACCEPT | Summary: Gsta4's glutathione conjugation of lipid peroxidation products and xenobiotic electrophiles supports retaining glutathione transferase activity as a direct annotation (ISO, GO_REF:0000121; donor mouse Gsta4, MGI:MGI:1309515). Reason: glutathione transferase activity is a specific catalytic activity matching Gsta4's documented role in glutathione conjugation of lipid peroxidation products and xenobiotic electrophiles. The donor is the mouse Gsta4 ortholog (MGI:MGI:1309515), a one-to-one ortholog whose GSH-conjugating activity toward 4-HNE is well established; transfer of the shared catalytic activity is sound. Supporting Evidence: UniProtKB:P14942 Reaction=RX + glutathione = an S-substituted glutathione + a halide anion + H(+) UniProtKB:P14942 FUNCTION: Conjugation of reduced glutathione to a wide number of exogenous and endogenous hydrophobic electrophiles. |
| GO:0004364 glutathione transferase activity | ISO GO_REF:0000121 | ACCEPT | Summary: Glutathione transferase activity transferred by orthology from human GSTA4 (UniProtKB:O15217); donor-split duplicate of the mouse-donor ISO row and consistent with the IBA and IEA rows for the same activity. Reason: The donor is human GSTA4 (UniProtKB:O15217), the one-to-one ortholog of rat Gsta4, whose GSTA4-4 enzyme has been characterized kinetically as a highly efficient GSH conjugator of 4-HNE and other lipid alkenals. Glutathione transferase activity is the shared catalytic activity of the alpha-class GSTs and is directly supported for rat GSTA4-4 by mitochondrial and cytosolic 4-HNE-specific GST activity in rat tissues, so the transfer is sound. Supporting Evidence: UniProtKB:P14942 FUNCTION: Conjugation of reduced glutathione to a wide number of exogenous and endogenous hydrophobic electrophiles. PMID:9774145 it also increased 4-hydroxynonenal specific GST A4-4 activity in the brain and lung mitochondrial matrix fraction file:rat/Gsta4/Gsta4-deep-research-falcon.md A major cellular clearance pathway is **GSH conjugation (Michael addition)** catalyzed predominantly by **GSTA4-4**. |
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Download this section (compressed HTML)Q: Falcon deep research highlights Scian et al. 2023 (Biomolecules, DOI:10.3390/biom13020329) showing GSTA4-4 catalyzes the retro-Michael reaction (GS-alkenal -> GSH + alkenal) with low commitment to forward catalysis, supporting a homeostatic/regulatory role in setting steady-state lipid alkenal pools rather than purely unidirectional detoxification. Does this reversibility/set-point framing warrant a new or modified BP annotation (e.g., capturing alkenal homeostasis or regulation of reactive lipid signaling) beyond the current detoxification/xenobiotic-metabolism terms?
Suggested experts: William M. Atkins
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