GLO1 (GOX1, At3g14420) encodes one of the two major leaf glycolate oxidases of Arabidopsis, a peroxisomal FMN-dependent (S)-2-hydroxy-acid oxidase that oxidizes glycolate to glyoxylate with O2, producing H2O2. The recombinant enzyme has glycolate oxidase activity with kinetics close to those of its tandem paralog GLO2 (GOX2, At3g14415). In the photorespiratory C2 cycle it catalyzes the peroxisomal glycolate-to-glyoxylate step, and its H2O2 product is removed by catalase (CAT2). GOX1 and GOX2 are co-regulated with other photorespiratory genes and are largely redundant in air, so single mutants grow normally while combined knock-down causes a severe photorespiratory phenotype; GOX1 is the more important isoform under high photorespiratory flux and in a catalase-deficient background. H2O2 generated by glycolate oxidase also contributes to defence signalling during nonhost and gene-for-gene resistance. Note that the GOX1/GOX2 names for At3g14420/At3g14415 are crossed in part of the literature.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0003729 mRNA binding | IDA PMID:32344669 Discovering the RNA-Binding Proteome of Plant Leaves with an... | MARK AS OVER ANNOTATED | Summary: Leaf RNA interactome capture (ptRIC) recovered (S)-2-hydroxy-acid oxidase among metabolic enzymes crosslinked to poly(A) RNA. Reason: The cited proteome-wide RNA interactome capture lists (S)-2-hydroxy-acid oxidase as a putative moonlighting RNA-binding enzyme, without validation of specific mRNA targets, binding site or any consequence for RNA fate. The paper itself notes that further experiments are needed for such unconventional RBPs. GLO1 is a highly abundant peroxisomal matrix enzyme; capture of abundant metabolic enzymes in RIC is common and does not establish mRNA binding as a function of the protein. The observation is not contradicted, but the MF annotation over-states what was shown. Supporting Evidence: PMID:32344669 Additional moonlighting enzymes were identified in the leaf RBPome, such as COBALAMIN-INDEPENDENT METHIONINE SYNTHASE, (S)-2-HYDROXY-ACID OXIDASE, GLYCINE DEHYDROGENASE and GLUTAMATE-GLYOXYLATE AMINOTRANSFERASE |
| GO:0003973 (S)-2-hydroxy-acid oxidase activity | IBA GO_REF:0000033 | ACCEPT | Summary: Phylogenetic inference of (S)-2-hydroxy-acid oxidase activity (GO:0003973, which now covers the obsolete glycolate oxidase activity term GO:0008891) for GLO1. Reason: Core function. GLO1 is a member of the FMN-dependent alpha-hydroxy acid dehydrogenase family, and recombinant AtGOX1 (At3g14420) was purified and assayed with glycolate (PMID:25416784), giving Km 0.22 mM and kcat about 30 s-1 per UniProt. The PAINT node is seeded by the paralogous GLO2 (At3g14415), which has direct experimental activity (PMID:21828292, PMID:25416784), and GLO1 sits inside that clade. GO:0003973 is the correct term; GO:0008891 glycolate oxidase activity is obsolete and replaced by GO:0003973 (verified in OLS). Supporting Evidence: file:ARATH/GLO1/GLO1-uniprot.txt Catalyzes the oxidation of glycolate to glyoxylate, with a reduction of O2 to H2O2 PMID:25416784 Kinetic parameters of purified recombinant GOX1 (At3g14420) and GOX2 (At3g14415) from A. thaliana (the two GOX genes highly expressed in leaves) PMID:25416784 For each GOX tested, their catalytic activities were measured over a range of glycolate concentrations file:ARATH/GLO1/GLO1-uniprot.txt Belongs to the FMN-dependent alpha-hydroxy acid dehydrogenase family. |
| GO:0003973 (S)-2-hydroxy-acid oxidase activity | IEA GO_REF:0000003 | ACCEPT | Summary: EC 1.1.3.15 (glycolate oxidase) mapping to (S)-2-hydroxy-acid oxidase activity. Reason: The EC 1.1.3.15 assignment is experimentally supported for GLO1 (recombinant enzyme oxidizes glycolate, PMID:25416784) and the mapping to GO:0003973 is correct. Supporting Evidence: file:ARATH/GLO1/GLO1-uniprot.txt Catalyzes the oxidation of glycolate to glyoxylate, with a reduction of O2 to H2O2 PMID:25416784 For each GOX tested, their catalytic activities were measured over a range of glycolate concentrations |
| GO:0005634 nucleus | HDA PMID:14617066 Analysis of the Arabidopsis nuclear proteome and its respons... | MARK AS OVER ANNOTATED | Summary: Detected in a 2-D gel/MALDI-TOF survey of the Arabidopsis nuclear proteome. Reason: Glycolate oxidase is a soluble peroxisomal matrix enzyme with a C-terminal PTS1 and is one of the most abundant proteins of photosynthetic leaves; it was identified in purified leaf peroxisomes (PMID:17951448) and acts there in the C2 cycle (PMID:22303256). Detection in a bulk organelle or fraction proteome of this kind is most simply explained by carry-over of peroxisomes or peroxisomal matrix protein (peroxisomes are physically appressed to chloroplasts in leaf cells), and no targeted study shows a functional pool of GOX in this compartment. The high-throughput detection is not contradicted, but it does not describe where the enzyme acts. Action follows the ARATH convention for single high-throughput proteomics location hits (projects/ARATH/organelle-audit.md, rule 3). There is no nuclear-localization signal or nuclear role reported for glycolate oxidase. Supporting Evidence: PMID:17951448 both isoforms of glycolate oxidase (GOX), GOX1 (At3g14415; PRL>) and GOX2 (At3g14420; ARL>), were specifically identified |
| GO:0005737 cytoplasm | ISM GO_REF:0000122 | MODIFY | Summary: AtSubP sequence-based prediction of cytoplasmic location. Reason: Cytoplasm is technically true (the peroxisome is part of the cytoplasm), but it is far less specific than the supported location. GLO1 carries a C-terminal PTS1 (ARL>) and was identified in purified leaf peroxisomes (PMID:17951448, where At3g14420 is called GOX2). Replace with peroxisome, which the gene already carries by HDA, IBA and IEA. Proposed replacements: peroxisome Supporting Evidence: PMID:17951448 both isoforms of glycolate oxidase (GOX), GOX1 (At3g14415; PRL>) and GOX2 (At3g14420; ARL>), were specifically identified |
| GO:0005777 peroxisome | HDA PMID:17951448 Proteome analysis of Arabidopsis leaf peroxisomes reveals no... | ACCEPT | Summary: Identified by mass spectrometry in purified Arabidopsis leaf peroxisomes, distinguished from its paralog by isoform-specific peptides. Reason: Core location. The leaf peroxisome proteome specifically identified At3g14420 (named GOX2 in this paper, which uses the crossed GOX1/GOX2 naming) and its PTS1 ARL>. Glycolate oxidation in the peroxisome is the photorespiratory step (PMID:22303256). Supporting Evidence: PMID:17951448 both isoforms of glycolate oxidase (GOX), GOX1 (At3g14415; PRL>) and GOX2 (At3g14420; ARL>), were specifically identified |
| GO:0005777 peroxisome | IBA GO_REF:0000033 | ACCEPT | Summary: Phylogenetic inference that GLO1 is active in the peroxisome. Reason: Consistent with direct proteomic identification in leaf peroxisomes (PMID:17951448) and the conserved peroxisomal location of plant and animal short-chain 2-hydroxy-acid oxidases. Supporting Evidence: PMID:17951448 both isoforms of glycolate oxidase (GOX), GOX1 (At3g14415; PRL>) and GOX2 (At3g14420; ARL>), were specifically identified |
| GO:0005777 peroxisome | IEA GO_REF:0000044 | ACCEPT | Summary: UniProt subcellular location (Peroxisome) mapped to GO. Reason: Supported by the leaf peroxisome proteome (PMID:17951448). Supporting Evidence: PMID:17951448 both isoforms of glycolate oxidase (GOX), GOX1 (At3g14415; PRL>) and GOX2 (At3g14420; ARL>), were specifically identified |
| GO:0005829 cytosol | HDA PMID:25293756 A proteomic strategy for global analysis of plant protein co... | MARK AS OVER ANNOTATED | Summary: Detected in a size-exclusion chromatography/proteomic survey of soluble protein complexes. Reason: GLO1 is a PTS1 peroxisomal matrix enzyme identified in purified leaf peroxisomes (PMID:17951448), and the Arabidopsis cytosolic proteome analysis gave a curated NOT cytosol (RCA) row for it (PMID:21166475, accepted here). Soluble extracts used in complex-profiling studies include peroxisomal matrix protein released during extraction, which explains the detection of this very abundant leaf enzyme; GLO1 is translated in the cytosol before import, but no functional cytosolic pool has been reported. The NOT row is a computational (RCA) judgement, not an experimental NOT, so this HDA hit is marked as over-annotated rather than removed, following projects/ARATH/organelle-audit.md (rules 3 and 4). Supporting Evidence: PMID:17951448 both isoforms of glycolate oxidase (GOX), GOX1 (At3g14415; PRL>) and GOX2 (At3g14420; ARL>), were specifically identified |
| GO:0005829 cytosol | RCA NOT PMID:21166475 Analysis of the Arabidopsis cytosolic proteome highlights su... | ACCEPT | Summary: NOT located in cytosol, from analysis of the Arabidopsis cytosolic proteome. Reason: Consistent with the biology: GLO1 is a PTS1 peroxisomal matrix enzyme (PMID:17951448), and the steady-state enzyme acts in the peroxisome rather than the cytosol. The abstract-only cache does not show the GLO1-specific data, so the curator's assessment is deferred to. The positive cytosol HDA row is marked as over-annotated (projects/ARATH/organelle-audit.md, rule 3); the two rows take different actions because they make opposite claims. Supporting Evidence: PMID:17951448 both isoforms of glycolate oxidase (GOX), GOX1 (At3g14415; PRL>) and GOX2 (At3g14420; ARL>), were specifically identified |
| GO:0009506 plasmodesma | HDA PMID:21533090 Arabidopsis plasmodesmal proteome. | MARK AS OVER ANNOTATED | Summary: Detected in a plasmodesma-enriched cell wall fraction proteome. Reason: Glycolate oxidase is a soluble peroxisomal matrix enzyme with a C-terminal PTS1 and is one of the most abundant proteins of photosynthetic leaves; it was identified in purified leaf peroxisomes (PMID:17951448) and acts there in the C2 cycle (PMID:22303256). Detection in a bulk organelle or fraction proteome of this kind is most simply explained by carry-over of peroxisomes or peroxisomal matrix protein (peroxisomes are physically appressed to chloroplasts in leaf cells), and no targeted study shows a functional pool of GOX in this compartment. The high-throughput detection is not contradicted, but it does not describe where the enzyme acts. Action follows the ARATH convention for single high-throughput proteomics location hits (projects/ARATH/organelle-audit.md, rule 3). Supporting Evidence: PMID:17951448 both isoforms of glycolate oxidase (GOX), GOX1 (At3g14415; PRL>) and GOX2 (At3g14420; ARL>), were specifically identified |
| GO:0009507 chloroplast | HDA PMID:18431481 Sorting signals, N-terminal modifications and abundance of t... | MARK AS OVER ANNOTATED | Summary: Detected in a large-scale chloroplast proteome (Zybailov et al. 2008). Reason: Glycolate oxidase is a soluble peroxisomal matrix enzyme with a C-terminal PTS1 and is one of the most abundant proteins of photosynthetic leaves; it was identified in purified leaf peroxisomes (PMID:17951448) and acts there in the C2 cycle (PMID:22303256). Detection in a bulk organelle or fraction proteome of this kind is most simply explained by carry-over of peroxisomes or peroxisomal matrix protein (peroxisomes are physically appressed to chloroplasts in leaf cells), and no targeted study shows a functional pool of GOX in this compartment. The high-throughput detection is not contradicted, but it does not describe where the enzyme acts. Action follows the ARATH convention for single high-throughput proteomics location hits (projects/ARATH/organelle-audit.md, rule 3). GLO1 has no chloroplast transit peptide. Supporting Evidence: PMID:17951448 both isoforms of glycolate oxidase (GOX), GOX1 (At3g14415; PRL>) and GOX2 (At3g14420; ARL>), were specifically identified |
| GO:0009570 chloroplast stroma | HDA PMID:18633119 Quantitative proteomics of a chloroplast SRP54 sorting mutan... | MARK AS OVER ANNOTATED | Summary: Detected in chloroplast/stroma proteomics of a cpSRP54 mutant. Reason: Glycolate oxidase is a soluble peroxisomal matrix enzyme with a C-terminal PTS1 and is one of the most abundant proteins of photosynthetic leaves; it was identified in purified leaf peroxisomes (PMID:17951448) and acts there in the C2 cycle (PMID:22303256). Detection in a bulk organelle or fraction proteome of this kind is most simply explained by carry-over of peroxisomes or peroxisomal matrix protein (peroxisomes are physically appressed to chloroplasts in leaf cells), and no targeted study shows a functional pool of GOX in this compartment. The high-throughput detection is not contradicted, but it does not describe where the enzyme acts. Action follows the ARATH convention for single high-throughput proteomics location hits (projects/ARATH/organelle-audit.md, rule 3). The abstract itself discusses up-regulation of the photorespiratory pathway in peroxisomes and mitochondria, i.e. these enzymes were observed but are not plastid residents. Supporting Evidence: PMID:17951448 both isoforms of glycolate oxidase (GOX), GOX1 (At3g14415; PRL>) and GOX2 (At3g14420; ARL>), were specifically identified |
| GO:0009854 oxidative photosynthetic carbon pathway | IEA GO_REF:0000041 | ACCEPT | Summary: UniPathway mapping (photorespiration; glycine from 2-phosphoglycolate) to the oxidative photosynthetic carbon pathway (C2 cycle), a child of photorespiration. Reason: Core process. GLO1 catalyzes the peroxisomal glycolate-to-glyoxylate step of the C2 cycle. GOX1 and GOX2 are co-regulated with photorespiratory genes (PMID:22303256) and share a redundant photorespiratory role; their joint knock-down gives a severe air-grown phenotype (PMID:26896850), and loss of GOX1 specifically impairs glycolate processing under high photorespiratory flux (PMID:27225899). GO:0009854 is part_of GO:0009853 photorespiration and is the most precise term available. The core function nonetheless uses the broader GO:0009853 photorespiration, so that every C2-cycle step and ammonia refixation share one process term (see modules/photorespiration_c2_cycle.yaml). Supporting Evidence: file:ARATH/GLO1/GLO1-uniprot.txt Photosynthesis; photorespiration; glycine from 2-phosphoglycolate: step 2/3. PMID:22303256 Two of these genes (At3g14415 and At3g14420) are transcriptionally co-regulated with other photorespiratory genes PMID:26896850 We show that two Arabidopsis genes, GOX1 and GOX2, share a redundant photorespiratory role. PMID:26896850 Air-grown amiRgox1/2 plants with a residual 5% GOX activity exhibited a severe growth phenotype. PMID:27225899 the negative consequences of severe photorespiration were more pronounced in the absence of GOX1, which was accompanied with lesser ability to process glycolate. |
| GO:0010181 FMN binding | IEA GO_REF:0000002 | ACCEPT | Summary: InterPro (alpha-hydroxy acid dehydrogenase, FMN-dependent) mapping to FMN binding. Reason: Glycolate oxidase is a flavoprotein that uses FMN as its prosthetic group; FMN-binding residues are conserved with spinach GOX (UniProt, by similarity to P05414). Binding of the cofactor is intrinsic to the catalytic activity. Supporting Evidence: PMID:22303256 Glycolate oxidase (GO, EC 1.1.3.15) belongs to the class of flavindependent 2-hydroxy acid oxidases and catalyzes the oxidation of glycolate to glyoxylate. file:ARATH/GLO1/GLO1-uniprot.txt Belongs to the FMN-dependent alpha-hydroxy acid dehydrogenase family. |
| GO:0016491 oxidoreductase activity | IEA GO_REF:0000002 | MODIFY | Summary: InterPro mapping to the generic oxidoreductase activity term. Reason: Correct but uninformative; the specific activity, (S)-2-hydroxy-acid oxidase activity (GO:0003973), is a descendant of oxidoreductase activity and is already carried by GLO1 with experimental support (PMID:25416784). Proposed replacements: (S)-2-hydroxy-acid oxidase activity Supporting Evidence: file:ARATH/GLO1/GLO1-uniprot.txt Catalyzes the oxidation of glycolate to glyoxylate, with a reduction of O2 to H2O2 |
| GO:0022626 cytosolic ribosome | HDA PMID:15821981 High heterogeneity within the ribosomal proteins of the Arab... | MARK AS OVER ANNOTATED | Summary: Co-purified with cytosolic 80S ribosomes in a ribosome proteomics study. Reason: Glycolate oxidase is a soluble peroxisomal matrix enzyme with a C-terminal PTS1 and is one of the most abundant proteins of photosynthetic leaves; it was identified in purified leaf peroxisomes (PMID:17951448) and acts there in the C2 cycle (PMID:22303256). Detection in a bulk organelle or fraction proteome of this kind is most simply explained by carry-over of peroxisomes or peroxisomal matrix protein (peroxisomes are physically appressed to chloroplasts in leaf cells), and no targeted study shows a functional pool of GOX in this compartment. The high-throughput detection is not contradicted, but it does not describe where the enzyme acts. Action follows the ARATH convention for single high-throughput proteomics location hits (projects/ARATH/organelle-audit.md, rule 3). The paper reports a number of non-ribosomal proteins that co-migrate with 80S ribosomes; GLO1 is not a ribosomal component. Supporting Evidence: PMID:17951448 both isoforms of glycolate oxidase (GOX), GOX1 (At3g14415; PRL>) and GOX2 (At3g14420; ARL>), were specifically identified |
| GO:0042742 defense response to bacterium | IEA GO_REF:0000117 | KEEP AS NON CORE | Summary: ARBA machine-learning annotation to defense response to bacterium. Reason: Agrees with the experimental IMP row from Rojas et al. 2012 (PMID:22286136): gox T-DNA mutants are compromised in nonhost resistance to bacterial pathogens and accumulate less H2O2. This is a secondary role of the H2O2 product, not the core metabolic function. Supporting Evidence: PMID:22286136 GOX-silenced N. benthamiana and Arabidopsis thaliana GOX T-DNA insertion mutants are compromised for nonhost resistance. |
| GO:0042742 defense response to bacterium | IMP PMID:22286136 Glycolate oxidase modulates reactive oxygen species-mediated... | KEEP AS NON CORE | Summary: Arabidopsis gox T-DNA mutants are compromised for nonhost resistance and show reduced H2O2, callose deposition and electrolyte leakage after nonhost bacterial inoculation. Reason: The cached text is abstract-only. The abstract names haox2 and gox3 for the gene-expression work, but Kerchev et al. 2016 (PMID:27225899) state in their full text that the gox1-1 and gox2-1 alleles were described in Rojas et al. 2012, consistent with the curator's IMP annotation to GLO1. Deferring to the curator. GOX-derived H2O2 contributing to defence is plausible but secondary to the photorespiratory role. Supporting Evidence: PMID:22286136 GOX-silenced N. benthamiana and Arabidopsis thaliana GOX T-DNA insertion mutants are compromised for nonhost resistance. PMID:22286136 Arabidopsis gox mutants have lower H(2)O(2) accumulation, reduced callose deposition, and reduced electrolyte leakage upon inoculation with hypersensitive response-causing nonhost pathogens. |
| GO:0047639 alcohol oxidase activity | IEA GO_REF:0000116 | MODIFY | Summary: Rhea mapping (RHEA:25311 glycolate + O2 = glyoxylate + H2O2) to alcohol oxidase activity. Reason: GO:0047639 alcohol oxidase activity is defined as primary alcohol + O2 = aldehyde + H2O2 and is a sibling, not a parent, of GO:0003973 in GO. Although glycolate formally has a primary alcohol group, the reaction is the oxidation of a 2-hydroxy acid to a 2-oxo acid, which is what GO:0003973 (S)-2-hydroxy-acid oxidase activity describes (and the term that replaced obsolete glycolate oxidase activity). Replace with GO:0003973. Proposed replacements: (S)-2-hydroxy-acid oxidase activity Supporting Evidence: file:ARATH/GLO1/GLO1-uniprot.txt Catalyzes the oxidation of glycolate to glyoxylate, with a reduction of O2 to H2O2 PMID:22303256 Glycolate oxidase (GO, EC 1.1.3.15) belongs to the class of flavindependent 2-hydroxy acid oxidases and catalyzes the oxidation of glycolate to glyoxylate. |
| GO:0048046 apoplast | HDA PMID:18538804 Hydroponic isotope labelling of entire plants (HILEP) for qu... | MARK AS OVER ANNOTATED | Summary: Detected in an apoplast-focused quantitative proteomics study (HILEP) under oxidative stress. Reason: Glycolate oxidase is a soluble peroxisomal matrix enzyme with a C-terminal PTS1 and is one of the most abundant proteins of photosynthetic leaves; it was identified in purified leaf peroxisomes (PMID:17951448) and acts there in the C2 cycle (PMID:22303256). Detection in a bulk organelle or fraction proteome of this kind is most simply explained by carry-over of peroxisomes or peroxisomal matrix protein (peroxisomes are physically appressed to chloroplasts in leaf cells), and no targeted study shows a functional pool of GOX in this compartment. The high-throughput detection is not contradicted, but it does not describe where the enzyme acts. Action follows the ARATH convention for single high-throughput proteomics location hits (projects/ARATH/organelle-audit.md, rule 3). GLO1 has no signal peptide, and apoplastic extracts of stressed leaves commonly contain abundant intracellular proteins. Supporting Evidence: PMID:17951448 both isoforms of glycolate oxidase (GOX), GOX1 (At3g14415; PRL>) and GOX2 (At3g14420; ARL>), were specifically identified |
| GO:0050665 hydrogen peroxide biosynthetic process | IEA GO_REF:0000117 | KEEP AS NON CORE | Summary: ARBA machine-learning annotation to hydrogen peroxide biosynthetic process. Reason: H2O2 is a direct product of the glycolate oxidase reaction, so GLO1 does catalyze H2O2 formation; this is a true but secondary process view of the core activity. Kept as non-core alongside the IMP row. Supporting Evidence: PMID:22303256 Molecular oxygen is used as a co-substrate and, thus, H 2 O 2 is produced by the enzyme. |
| GO:0050665 hydrogen peroxide biosynthetic process | IMP PMID:22286136 Glycolate oxidase modulates reactive oxygen species-mediated... | KEEP AS NON CORE | Summary: gox mutants accumulate less H2O2 after nonhost pathogen inoculation. Reason: GOX produces H2O2 stoichiometrically from glycolate oxidation (PMID:22303256) and the mutants show lower H2O2 accumulation during defence (abstract of PMID:22286136; full text not cached, curator deferred to). Non-core: H2O2 is a by-product of the photorespiratory step. Supporting Evidence: PMID:22286136 Arabidopsis gox mutants have lower H(2)O(2) accumulation, reduced callose deposition, and reduced electrolyte leakage upon inoculation with hypersensitive response-causing nonhost pathogens. PMID:22286136 Here we show that GOX is an alternative source for the production of H(2)O(2) during both gene-for-gene and nonhost resistance responses. PMID:22303256 Molecular oxygen is used as a co-substrate and, thus, H 2 O 2 is produced by the enzyme. |
Loading supporting content…
Download this section (compressed HTML)Q: GOA has an EXP (S)-2-hydroxy-acid oxidase activity row for GLO2 from PMID:25416784 but none for GLO1, although the same paper purified and assayed recombinant GOX1 (At3g14420). Should a matching experimental annotation be added to GLO1, and was the omission caused by the crossed GOX1/GOX2 naming in the literature?
Q: GOX1 and GOX2 are described as nearly identical (PMID:27225899) and are kinetically similar in vitro (PMID:25416784), yet loss of GOX1 but not GOX2 suppresses the cat2 phenotype (PMID:27225899). Is this difference due to expression level, protein abundance in peroxisomes, or regulation such as the reported S-nitrosylation of GOX1?
Experiment: Quantify GOX1 and GOX2 protein abundance separately in leaf peroxisomes (isoform-specific peptides) under low and high light, and test whether a Cys-343 non-nitrosylatable GOX1 variant changes the cat2 suppression phenotype.
Loading supporting content…
Download this section (compressed HTML)Loading supporting content…
Download this section (compressed HTML)