GLO1 is a predominantly cytosolic, zinc-dependent homodimeric lactoylglutathione lyase that catalyzes the first enzymatic step of the glyoxalase pathway. It converts the hemimercaptal formed spontaneously from methylglyoxal and glutathione into S-lactoylglutathione, enabling glyoxalase II to complete methylglyoxal detoxification and regenerate glutathione. Each active site lies at the dimer interface and uses an essential zinc ion and a catalytic glutamate to stabilize and protonate a cis-enediolate intermediate. Native human GLO1 is redox-regulated: glutathionylation of Cys139 inhibits activity. Elevated GLO1 can attenuate chemotherapy-induced apoptosis in experimental cancer-cell contexts, but this is downstream, context-specific biology rather than a separate constitutive molecular activity.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0004462 lactoylglutathione lyase activity | IEA GO_REF:0000120 | ACCEPT | Summary: Combined automated methods assign the canonical glyoxalase I activity from family, reaction, and orthology evidence. Reason: Direct human cDNA expression, purified-enzyme activity, active-site mutagenesis, and multiple inhibitor/transition-state structures establish that GLO1 catalyzes conversion of the methylglyoxal-glutathione hemimercaptal to S-lactoylglutathione. Supporting Evidence: PMID:7684374 Glyoxalase I (EC 4.4.1.5) catalyzes the transformation of methylglyoxal and glutathione to S-lactoylglutathione. |
| GO:0046872 metal ion binding | IEA GO_REF:0000002 | MODIFY | Summary: InterPro assigns generic metal-ion binding from the glyoxalase I conserved domain. Reason: The active-site metal is specifically zinc, demonstrated by crystal structures, metal analysis, and mutagenesis. The specific zinc ion binding term is more informative than generic metal ion binding. Proposed replacements: zinc ion binding Supporting Evidence: PMID:9218781 The zinc metalloenzyme glyoxalase I catalyses the glutathione-dependent inactivation of toxic methylglyoxal. |
| GO:0005515 protein binding | IPI PMID:32296183 A reference map of the human binary protein interactome. | MARK AS OVER ANNOTATED | Summary: HuRI reports a high-throughput binary interaction between GLO1 and PUS10. Reason: A single binary-interactome observation without a demonstrated functional consequence does not define GLO1's molecular activity. Generic protein binding obscures the well-established lactoylglutathione lyase function. |
| GO:0006749 glutathione metabolic process | IEA GO_REF:0000107 | ACCEPT | Summary: Ensembl transfers participation in glutathione metabolism from mammalian orthologs. Reason: GLO1 acts directly on the spontaneously formed glutathione-methylglyoxal hemimercaptal in the glyoxalase cycle, whose second enzyme regenerates free glutathione. This is a direct biochemical pathway role, although methylglyoxal catabolism is the more informative process description. Supporting Evidence: PMID:20454679 Glo1 (S-D-lactoylglutathione lyase) and Glo2 (hydroxyacyl glutathione hydrolase) convert the spontaneously formed hemithioacetal between glutathione (GSH) and MGO into D-lactate and free GSH. |
| GO:0008270 zinc ion binding | IEA GO_REF:0000107 | ACCEPT | Summary: Ensembl transfers zinc-ion binding from experimentally characterized mammalian orthologs. Reason: Human structures and metal-ligand mutagenesis independently establish one essential zinc ion per subunit at the intersubunit active sites. Supporting Evidence: PMID:9218781 the active site being situated in the dimer interface, with the inhibitor and essential zinc ion interacting with side chains from both subunits |
| GO:0009438 methylglyoxal metabolic process | IEA GO_REF:0000107 | MODIFY | Summary: Ensembl transfers participation in methylglyoxal metabolism from mammalian orthologs. Reason: The human enzyme is directly shown to detoxify and break down methylglyoxal, so the directionally specific child term methylglyoxal catabolic process is more informative than the generic metabolic-process term. Proposed replacements: methylglyoxal catabolic process Supporting Evidence: PMID:7684374 The Escherichia coli cells carrying the expression vector of this cDNA acquired methylglyoxal resistance and the cell lysate showed the high activity of glyoxalase I. |
| GO:0030316 osteoclast differentiation | IEA GO_REF:0000107 | KEEP AS NON CORE | Summary: Ensembl transfers an osteoclast-differentiation phenotype from mouse Glo1. Reason: The cross-species inference is biologically plausible and agrees with the curator ISS record, but no direct human experiment was found. It is retained as a non-core mammalian developmental phenotype rather than used to define GLO1's conserved catalytic role. |
| GO:0005829 cytosol | IDA PMID:20454679 Posttranslational modification of human glyoxalase 1 indicat... | ACCEPT | Summary: Native human erythrocyte GLO1 was biochemically characterized as a cytosolic enzyme. Reason: Cytosol is the expected and experimentally coherent functional location for the soluble methylglyoxal-detoxifying enzyme. Supporting Evidence: PMID:20454679 Glyoxalase 1 (Glo1) and glyoxalase 2 (Glo2) are ubiquitously expressed cytosolic enzymes |
| GO:0005654 nucleoplasm | IDA GO_REF:0000052 | KEEP AS NON CORE | Summary: Human Protein Atlas immunofluorescence detects a nucleoplasmic GLO1 signal. Reason: The localization observation is retained, but no primary study reviewed here demonstrates a nucleoplasm-specific catalytic function. The well-supported functional pool is cytosolic. |
| GO:0005829 cytosol | IDA GO_REF:0000052 | ACCEPT | Summary: Human Protein Atlas immunofluorescence detects cytosolic GLO1. Reason: This localization agrees with direct biochemical characterization of native GLO1 and with its soluble methylglyoxal-detoxifying function. Supporting Evidence: PMID:20454679 Glyoxalase 1 (Glo1) and glyoxalase 2 (Glo2) are ubiquitously expressed cytosolic enzymes |
| GO:0005886 plasma membrane | IDA GO_REF:0000052 | KEEP AS NON CORE | Summary: Human Protein Atlas immunofluorescence reports a plasma-membrane GLO1 signal. Reason: The experimental localization is retained, but no source reviewed here establishes a membrane-specific GLO1 activity or membrane-targeting mechanism. It should not displace the cytosolic core location. |
| GO:0004462 lactoylglutathione lyase activity | IDA PMID:20454679 Posttranslational modification of human glyoxalase 1 indicat... | ACCEPT | Summary: Purified native human GLO1 was assayed with methylglyoxal/glutathione and characterized kinetically under native and reducing conditions. Reason: Direct activity measurements and redox perturbation establish the canonical lactoylglutathione lyase reaction in native human enzyme. Supporting Evidence: PMID:20454679 Glutathionylation of Glo1 strongly inhibited enzyme activity at physiologically relevant concentration of GSH. |
| GO:0004462 lactoylglutathione lyase activity | IDA PMID:23122816 Design and evaluation of azaindole-substituted N-hydroxypyri... | ACCEPT | Summary: Human GLO1 inhibitor activity and binding were analyzed by structure-activity relationships, X-ray crystallography, and thermodynamic measurements. Reason: The curator had access to the full inhibitor study, and the assignment is fully coherent with multiple independent direct human enzyme studies. Supporting Evidence: PMID:23122816 We conducted a high throughput screening for glyoxalase I (GLO1) inhibitors |
| GO:0008270 zinc ion binding | IDA PMID:23122816 Design and evaluation of azaindole-substituted N-hydroxypyri... | ACCEPT | Summary: The inhibitor-bound human GLO1 structure includes the catalytic zinc center. Reason: Although the cached source is abstract-only, the curator's structural annotation is consistent with independent human crystal structures and metal-ligand mutagenesis. There is no basis to overrule it. Supporting Evidence: PMID:9218781 The zinc metalloenzyme glyoxalase I catalyses the glutathione-dependent inactivation of toxic methylglyoxal. |
| GO:0005829 cytosol | TAS Reactome:R-HSA-5694071 | ACCEPT | Summary: Reactome places the zinc-loaded GLO1 dimer reaction in the cytosol. Reason: Cytosolic placement is consistent with direct biochemical characterization and the localization of the glutathione-dependent methylglyoxal pathway. Supporting Evidence: PMID:20454679 Glyoxalase 1 (Glo1) and glyoxalase 2 (Glo2) are ubiquitously expressed cytosolic enzymes |
| GO:0070062 extracellular exosome | HDA PMID:23533145 In-depth proteomic analyses of exosomes isolated from expres... | KEEP AS NON CORE | Summary: GLO1 was detected in large-scale proteomics of expressed-prostatic-secretion urine exosome preparations. Reason: The high-throughput cargo observation is retained, but detection among roughly 900 proteins does not establish active secretion or an extracellular GLO1 pathway. Supporting Evidence: PMID:23533145 In pooled EPS-urine exosome samples, ~900 proteins were detected. |
| GO:0004462 lactoylglutathione lyase activity | IDA PMID:9705294 Involvement of an active-site Zn2+ ligand in the catalytic m... | ACCEPT | Summary: Purified wild-type and active-site mutants were assayed to define human GLO1 catalysis. Reason: Near-total loss of activity after mutation of zinc ligands and the catalytic glutamate directly establishes the enzyme activity and mechanism. Supporting Evidence: PMID:9705294 The results suggest that the metal ligand glutamate 172 is directly involved in the catalytic mechanism of the enzyme |
| GO:0008270 zinc ion binding | IDA PMID:9705294 Involvement of an active-site Zn2+ ligand in the catalytic m... | ACCEPT | Summary: Metal analysis and active-site mutagenesis directly characterize zinc binding in human GLO1. Reason: Zinc occupancy was measured in purified mutants, and the crystal structure showed zinc retained even in a catalytically inactive mutant. This is direct evidence for the essential metal-binding site. Supporting Evidence: PMID:9705294 Metal analysis demonstrated that mutant Q33E/E172Q contained 1.0 mol of zinc/mol of enzyme subunit |
| GO:0030316 osteoclast differentiation | ISS GO_REF:0000024 | KEEP AS NON CORE | Summary: A curator transfers an experimentally supported mouse Glo1 osteoclast phenotype to human GLO1 by sequence similarity. Reason: Curated orthology transfer is retained and agrees with the Ensembl IEA, but no direct human evidence was found. The phenotype is peripheral to the conserved zinc-dependent methylglyoxal-detoxification function. |
| GO:0070062 extracellular exosome | HDA PMID:19056867 Large-scale proteomics and phosphoproteomics of urinary exos... | KEEP AS NON CORE | Summary: GLO1 was detected in large-scale LC-MS/MS profiling of human urinary exosomes. Reason: Detection among 1,132 proteins is a valid proteomic cargo observation but does not demonstrate that exosomal GLO1 is catalytically active or normally secreted. It is retained outside the cytosolic core. Supporting Evidence: PMID:19056867 Overall, the analysis identified 1132 proteins unambiguously |
| GO:0004462 lactoylglutathione lyase activity | IDA PMID:11489834 Selective activation of apoptosis program by S-p-bromobenzyl... | ACCEPT | Summary: GLO1 activity was measured across human tumor cell lines and perturbed with a cell-permeable GLO1 inhibitor. Reason: Enzyme-activity measurements and selective pharmacological inhibition in human cells support the canonical GLO1 activity, consistent with direct purified-enzyme studies. Supporting Evidence: PMID:11489834 Glyoxalase I (GLO1) is an enzyme that plays a role in the detoxification of methylglyoxal, a side-product of glycolysis. |
| GO:0043066 negative regulation of apoptotic process | IMP PMID:10807791 Glyoxalase I is involved in resistance of human leukemia cel... | KEEP AS NON CORE | Summary: GLO1 overexpression suppresses chemotherapy-induced caspase activation and apoptosis, while inhibition resensitizes a resistant leukemia line. Reason: Gain-of-function and inhibitor perturbations directly support the term in drug-treated human leukemia cells. It is context-specific downstream biology, not the conserved catalytic core. Supporting Evidence: PMID:10807791 When overexpressed in human Jurkat cells, GLO1 inhibited etoposide- and adriamycin-induced caspase activation and apoptosis |
| GO:0043066 negative regulation of apoptotic process | IDA PMID:11489834 Selective activation of apoptosis program by S-p-bromobenzyl... | KEEP AS NON CORE | Summary: Pharmacological GLO1 inhibition preferentially induces apoptosis in human tumor cells with high GLO1 activity. Reason: The inverse perturbation supports an anti-apoptotic contribution of GLO1 in the tested cancer-cell context. It is retained as non-core because it does not establish a universal physiological apoptosis-regulatory activity. Supporting Evidence: PMID:11489834 Human lung cancer NCI-H522 and DMS114 cells, expressing higher GLO1 activity, underwent apoptosis when treated with BBGC, whereas A549 cells, expressing lower activity, did not. |
| GO:0005737 cytoplasm | TAS PMID:16130169 Proteomics of human umbilical vein endothelial cells applied... | ACCEPT | Summary: A HUVEC proteomic study was used for a traceable-author-statement cytoplasmic localization. Reason: The cached abstract does not expose the GLO1-specific result, but the broader cytoplasm term is independently and strongly supported by direct characterization of GLO1 as cytosolic. There is no basis to overrule the curator's source-level assessment. Supporting Evidence: PMID:20454679 Glyoxalase 1 (Glo1) and glyoxalase 2 (Glo2) are ubiquitously expressed cytosolic enzymes |
| GO:0043066 negative regulation of apoptotic process | TAS PMID:16130169 Proteomics of human umbilical vein endothelial cells applied... | KEEP AS NON CORE | Summary: A HUVEC proteomic apoptosis study was used for a traceable-author-statement annotation. Reason: The cached abstract does not expose a GLO1-specific directional result, so no source-specific mechanistic claim is made. Independent human GLO1 overexpression and inhibitor studies nevertheless support the same context-specific anti-apoptotic phenotype, and the curator's annotation is retained as non-core. Supporting Evidence: PMID:10807791 When overexpressed in human Jurkat cells, GLO1 inhibited etoposide- and adriamycin-induced caspase activation and apoptosis |
| GO:0005975 carbohydrate metabolic process | NAS PMID:7684374 Human glyoxalase I. cDNA cloning, expression, and sequence s... | MODIFY | Summary: The cloning paper links GLO1 to metabolism of methylglyoxal, a reactive by-product of carbohydrate metabolism. Reason: Carbohydrate metabolic process is too broad and obscures the experimentally demonstrated reaction direction. Methylglyoxal catabolic process precisely captures the enzyme's role. Proposed replacements: methylglyoxal catabolic process Supporting Evidence: PMID:7684374 The Escherichia coli cells carrying the expression vector of this cDNA acquired methylglyoxal resistance and the cell lysate showed the high activity of glyoxalase I. |
| GO:0004462 lactoylglutathione lyase activity | TAS PMID:7684374 Human glyoxalase I. cDNA cloning, expression, and sequence s... | ACCEPT | Summary: Human GLO1 cDNA expression confers high glyoxalase I activity and methylglyoxal resistance in bacteria. Reason: The cloning and heterologous-expression experiment directly links the human sequence to the canonical lactoylglutathione lyase reaction. Supporting Evidence: PMID:7684374 Glyoxalase I (EC 4.4.1.5) catalyzes the transformation of methylglyoxal and glutathione to S-lactoylglutathione. |
| GO:0110095 cellular detoxification of aldehyde | IMP PMID:7684374 Human glyoxalase I. cDNA cloning, expression, and sequence s... | NEW | Summary: Proposed new process annotation. Expression of human GLO1 confers resistance to the toxic aldehyde methylglyoxal while producing high glyoxalase I activity. Reason: The resistance phenotype directly demonstrates detoxification at the cellular level, and biochemical studies identify methylglyoxal as the aldehyde substrate. This term captures the protective process without overextending downstream disease associations. Supporting Evidence: PMID:7684374 The Escherichia coli cells carrying the expression vector of this cDNA acquired methylglyoxal resistance and the cell lysate showed the high activity of glyoxalase I. PMID:20454679 Glyoxalases (Glo1, E.C. 4.4.1.5, and Glo2, E.C.3.1.2.6) constitute an ubiquitous detoxification system that protects against cellular damage caused by reactive 2-oxo-aldehydes such as methylglyoxal (MGO). |
Loading supporting content…
Download this section (compressed HTML)Q: Does isoform 2 retain zinc-dependent catalytic activity or form activity-altering heterodimers with canonical GLO1?
Q: Are the nucleoplasmic and plasma-membrane immunofluorescence signals catalytically active endogenous pools?
Q: Can the cancer-cell apoptosis phenotype be separated genetically from methylglyoxal catalysis and from GLO1 phosphorylation/NO modification?
Experiment: Express and purify both isoforms, reconstitute defined homo- and heterodimers, and compare zinc occupancy, oligomer structure, and steady-state kinetics; then perform isoform-specific rescue in GLO1-null human cells under methylglyoxal challenge.
Hypothesis: Isoform 2 is catalytically impaired by its internal deletion and modulates canonical GLO1 through mixed-dimer formation.
Type: Isoform-resolved biochemistry and cellular complementation
Experiment: Rescue GLO1-null human cancer cells with wild-type protein, zinc-ligand or catalytic-glutamate mutants, and modification-site mutants at matched expression; quantify methylglyoxal flux, S-lactoylglutathione, caspase activation, and drug-induced apoptosis.
Hypothesis: Chemotherapy-resistance phenotypes require GLO1 catalysis rather than an independent scaffolding or signaling activity.
Type: Catalytic separation-of-function and metabolite phenotyping
Experiment: Combine endogenous fluorescent knock-in imaging with rigorous biochemical fractionation and compartment-targeted methylglyoxal reporters before and after oxidative or TNF stress.
Hypothesis: Nucleoplasmic and membrane-associated GLO1 signals are context-dependent pools with distinct methylglyoxal-detoxification capacity.
Type: Endogenous localization and compartment-specific activity assay
What is not known — curated, literature-grounded statements of the open unknowns (the inverse of core functions).
Gap: The catalytic competence and oligomeric behavior of splice isoform 2, which lacks residues 105-119 in the catalytic region, are unknown.
OPEN BIOLOGY MF_DARK
What is known: UniProt defines the in-frame deletion, but none of the reviewed activity or structural studies resolves this isoform or tests mixed dimers with canonical GLO1.
Significance: Because each active site spans the dimer interface, an inactive minor isoform could alter canonical enzyme activity through heterodimerization.
What would resolve it: Purify isoform 2 alone and in mixed dimers with isoform 1; measure zinc occupancy, hemimercaptal isomerization kinetics, and oligomer stoichiometry, followed by isoform-specific rescue in GLO1-null human cells.
Provenance (the field's own admissions):
Gap: It is unclear whether nucleoplasmic and plasma-membrane GLO1 signals represent stable, catalytically active pools.
OPEN BIOLOGY CC_DARK
What is known: HPA immunofluorescence supports localization observations, but the reviewed primary literature establishes cytosolic catalysis and provides no site-specific mechanism for the other compartments.
Significance: Resolving these pools is necessary before assigning nuclear or membrane pathway functions to GLO1.
What would resolve it: Validate endogenous localization with orthogonal antibodies and tagged knock-in alleles, fractionation controls, and compartment-targeted methylglyoxal flux/activity reporters.
Provenance (the field's own admissions):
Loading supporting content…
Download this section (compressed HTML)Loading supporting content…
Download this section (compressed HTML)Loading supporting content…
Download this section (compressed HTML)