Glutamate decarboxylase 1 (GAD67; 67 kDa glutamic acid decarboxylase) is a pyridoxal-5'-phosphate (PLP)-dependent decarboxylase (EC 4.1.1.15) that catalyzes the conversion of L-glutamate to gamma-aminobutyric acid (GABA) plus CO2, thereby producing the major inhibitory neurotransmitter of the central nervous system. It is the principal constitutively active GABA-synthesizing enzyme responsible for basal GABA production, whereas the paralog GAD2 (GAD65) is the synaptic-vesicle-associated isoform that is transiently activated on demand. The enzyme is a homodimer that covalently binds PLP at an active-site lysine and belongs to the group II decarboxylase family. GAD67 is a soluble cytosolic protein expressed predominantly in GABAergic neurons of the brain, with additional expression in some non-neural tissues. Bi-allelic loss-of-function variants cause an autosomal recessive developmental and epileptic encephalopathy, and hypomorphic missense variation has been associated with spastic cerebral palsy / spastic paraplegia phenotypes, consistent with its essential role in inhibitory neurotransmission.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0009449 GABA biosynthetic process | IBA GO_REF:0000033 | ACCEPT | Summary: Phylogenetic (IBA) annotation to GABA biosynthetic process. This is the core biological process of GAD1/GAD67 - synthesis of the inhibitory neurotransmitter GABA by decarboxylation of L-glutamate. Reason: GAD67 is the principal constitutive GABA-synthesizing enzyme; this process annotation is directly supported by structural/biochemical work and by the UniProt FUNCTION statement, and is consistent across orthologs used for the IBA inference. Supporting Evidence: PMID:17384644 GAD67 is constitutively active and is responsible for basal GABA production. file:human/GAD1/GAD1-uniprot.txt Catalyzes the synthesis of the inhibitory neurotransmitter |
| GO:0005737 cytoplasm | IBA GO_REF:0000033 | ACCEPT | Summary: Phylogenetic (IBA) annotation placing GAD1 activity in the cytoplasm. GAD67 is a soluble cytosolic enzyme, so this localization is correct, though the more specific term cytosol (GO:0005829) better captures the compartment. Reason: GAD67 lacks the N-terminal membrane-targeting modifications of GAD65 and acts as a soluble cytosolic enzyme; cytoplasm is a correct (if general) location. Cytosol is used as the specific location in core_functions. Supporting Evidence: file:human/GAD1/GAD1-uniprot.txt Belongs to the group II decarboxylase family |
| GO:0004351 glutamate decarboxylase activity | IBA GO_REF:0000033 | ACCEPT | Summary: Phylogenetic (IBA) annotation to glutamate decarboxylase activity (EC 4.1.1.15), the core molecular function of GAD1/GAD67. Reason: This is the defining catalytic activity of GAD67 and is independently supported by experimental (IDA) annotations from crystallographic and biochemical studies. Supporting Evidence: file:human/GAD1/GAD1-uniprot.txt L-glutamate + H(+) = 4-aminobutanoate + CO2 |
| GO:0048786 presynaptic active zone | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: Phylogenetic (IBA) annotation localizing GAD to the presynaptic active zone. This localization applies chiefly to synaptic GABA synthesis and is more characteristic of the vesicle-associated paralog GAD65; GAD67 is predominantly a soluble cytosolic enzyme responsible for basal GABA production. Reason: GAD67 can be present at synaptic terminals in GABAergic neurons and contribute to the presynaptic GABA pool, but its core activity is cytosolic basal GABA production rather than active-zone-restricted synthesis; retained as a non-core localization. Supporting Evidence: PMID:17384644 GAD67 is constitutively active and is responsible for basal GABA production. |
| GO:0004351 glutamate decarboxylase activity | IEA GO_REF:0000120 | ACCEPT | Summary: Electronic (ARBA) annotation to glutamate decarboxylase activity mapped via EC 4.1.1.15 / RHEA:17785. Redundant with the experimental and IBA annotations to the same term. Reason: Correct core molecular function; the EC/RHEA-based electronic mapping agrees with the experimentally established activity. Supporting Evidence: file:human/GAD1/GAD1-uniprot.txt L-glutamate + H(+) = 4-aminobutanoate + CO2 |
| GO:0016830 carbon-carbon lyase activity | IEA GO_REF:0000002 | MARK AS OVER ANNOTATED | Summary: InterPro-derived (IEA) annotation to carbon-carbon lyase activity, a broad parent of the specific glutamate decarboxylase activity. Reason: Not incorrect - glutamate decarboxylase activity IS a carbon-carbon lyase activity - but this parent term is far less informative than the specific EC 4.1.1.15 activity, which is captured by the more specific glutamate decarboxylase activity annotation. Supporting Evidence: file:human/GAD1/GAD1-uniprot.txt L-glutamate + H(+) = 4-aminobutanoate + CO2 |
| GO:0016831 carboxy-lyase activity | IEA GO_REF:0000002 | MARK AS OVER ANNOTATED | Summary: InterPro-derived (IEA) annotation to carboxy-lyase activity, the immediate lyase parent of glutamate decarboxylase activity. Reason: Correct as a parent (decarboxylases are carboxy-lyases) but uninformative relative to the specific glutamate decarboxylase activity term already annotated. Supporting Evidence: file:human/GAD1/GAD1-uniprot.txt L-glutamate + H(+) = 4-aminobutanoate + CO2 |
| GO:0030170 pyridoxal phosphate binding | IEA GO_REF:0000002 | ACCEPT | Summary: InterPro-derived (IEA) annotation to pyridoxal phosphate binding. PLP is the essential catalytic cofactor of GAD67, covalently bound as a Schiff base at the active-site lysine (Lys405). Reason: PLP binding is a genuine, core cofactor-binding function required for glutamate decarboxylase catalysis; independently supported by the crystal structure and UniProt COFACTOR/MOD_RES annotations. Supporting Evidence: file:human/GAD1/GAD1-uniprot.txt Name=pyridoxal 5 PMID:17384644 glutamic acid decarboxylase (GAD65 and |
| GO:0005515 protein binding | IPI PMID:16189514 Towards a proteome-scale map of the human protein-protein in... | MARK AS OVER ANNOTATED | Summary: Bare protein binding (IPI) from a proteome-scale yeast two-hybrid interactome screen (CCSB-HI1). Uninformative as to GAD1's molecular function. Reason: The generic protein binding term conveys no specific functional information and derives from a high-throughput binary interactome screen rather than a curated functional interaction; per curation guidelines the bare term is over-annotated. Retained (not removed) as it records a real experimental interaction. Supporting Evidence: PMID:16189514 an initial version of a proteome-scale map of |
| GO:0005515 protein binding | IPI PMID:17474147 Systematic identification of SH3 domain-mediated human prote... | MARK AS OVER ANNOTATED | Summary: Bare protein binding (IPI) from an SH3-domain peptide-array (PATS) systematic interaction screen. Reason: Uninformative generic protein binding derived from a high-throughput SH3 domain-ligand screen; no specific functional MF is conveyed. Retained as a recorded interaction rather than removed. Supporting Evidence: PMID:17474147 Systematic identification of SH3 domain-mediated human protein-protein |
| GO:0005515 protein binding | IPI PMID:21516116 Next-generation sequencing to generate interactome datasets. | MARK AS OVER ANNOTATED | Summary: Bare protein binding (IPI) from a next-generation-sequencing-based (Stitch-seq) high-throughput Y2H interactome dataset. Reason: Generic, uninformative protein binding from a proteome-scale interactome-mapping method; provides no specific molecular function. Kept as a recorded interaction. Supporting Evidence: PMID:21516116 massively parallel interactome-mapping pipeline, Stitch-seq |
| GO:0005515 protein binding | IPI PMID:25416956 A proteome-scale map of the human interactome network. | MARK AS OVER ANNOTATED | Summary: Bare protein binding (IPI) from a proteome-scale human binary interactome map (HI-II-14). Reason: Uninformative generic protein binding from a systematic binary interactome screen; no specific MF conveyed. Retained rather than removed as it records genuine high-throughput interaction data. Supporting Evidence: PMID:25416956 a systematic map of ?14,000 high-quality human |
| GO:0005515 protein binding | IPI PMID:26871637 Widespread Expansion of Protein Interaction Capabilities by ... | MARK AS OVER ANNOTATED | Summary: Bare protein binding (IPI) from an isoform-resolved interactome study of alternatively spliced ORFs. Reason: Generic protein binding from a high-throughput isoform interaction-profiling study; not an informative molecular function term. Kept as recorded interaction evidence. Supporting Evidence: PMID:26871637 Widespread Expansion of Protein Interaction Capabilities by Alternative |
| GO:0005515 protein binding | IPI PMID:31515488 Extensive disruption of protein interactions by genetic vari... | MARK AS OVER ANNOTATED | Summary: Bare protein binding (IPI) from a large-scale study of interaction disruption by human genetic variants (Y2H/PCA). Reason: Uninformative generic protein binding from a high-throughput variant-interactome screen; conveys no specific molecular function. Retained as a recorded interaction. Supporting Evidence: PMID:31515488 Extensive disruption of protein interactions by genetic variants |
| GO:0005515 protein binding | IPI PMID:32296183 A reference map of the human binary protein interactome. | MARK AS OVER ANNOTATED | Summary: Bare protein binding (IPI) from the HuRI human reference binary interactome map. Reason: Generic, uninformative protein binding from an all-by-all proteome-wide binary interactome screen; no specific MF is conveyed. Kept as a recorded interaction rather than removed. Supporting Evidence: PMID:32296183 reference interactome map of human binary protein interactions, or 'HuRI' |
| GO:0006540 GABA shunt | IEA GO_REF:0000107 | KEEP AS NON CORE | Summary: Electronic (Ensembl ortholog-transfer) annotation to the GABA shunt, the metabolic bypass in which glutamate is decarboxylated to GABA and GABA is subsequently transaminated and oxidized back into the TCA cycle. GAD1 catalyzes the entry (decarboxylation) step. Reason: GAD1 genuinely participates in the GABA shunt as the glutamate-decarboxylation step, but the shunt as a whole is a multi-enzyme metabolic process; the gene's core process is more precisely GABA biosynthesis. Retained as a non-core metabolic-context process. Supporting Evidence: file:human/GAD1/GAD1-uniprot.txt L-glutamate + H(+) = 4-aminobutanoate + CO2 |
| GO:0009449 GABA biosynthetic process | IEA GO_REF:0000120 | ACCEPT | Summary: Electronic (ARBA) annotation to GABA biosynthetic process, duplicating the IBA annotation to the same core biological process. Reason: Correct core process; the ARBA electronic mapping agrees with the phylogenetic and experimental evidence for GABA synthesis. Supporting Evidence: PMID:17384644 GAD67 is constitutively active and is responsible for basal GABA production. |
| GO:0006540 GABA shunt | IDA PMID:17384644 GABA production by glutamic acid decarboxylase is regulated ... | KEEP AS NON CORE | Summary: Experimental (IDA) annotation to the GABA shunt based on the structural/biochemical characterization of GAD67 catalyzing L-glutamate decarboxylation to GABA, the committed entry step of the shunt. Reason: Directly supported by experimental characterization of the decarboxylation step, but the shunt is a multi-enzyme metabolic process; GAD1's own core process is GABA biosynthesis. Deferring to the curator's experimental annotation, kept as non-core metabolic context. Supporting Evidence: PMID:17384644 GAD67 shows a tethered loop covering the active site, providing a catalytic |
| GO:0004351 glutamate decarboxylase activity | IDA PMID:17384644 GABA production by glutamic acid decarboxylase is regulated ... | ACCEPT | Summary: Experimental (IDA) annotation to glutamate decarboxylase activity from crystallographic and kinetic characterization of human GAD67, the definitive molecular function of the gene. Reason: This is the gold-standard experimental support for the core catalytic function; the structure shows a tethered catalytic loop sustaining constitutive GABA production. Supporting Evidence: PMID:17384644 GAD67 is constitutively active and is responsible for basal GABA production. |
| GO:0042802 identical protein binding | IDA PMID:17384644 GABA production by glutamic acid decarboxylase is regulated ... | ACCEPT | Summary: Experimental (IDA) annotation to identical protein binding, reflecting the fact that catalytically active GAD67 is a homodimer, as established by the crystal structure. Reason: Homodimerization is a structurally verified, functionally relevant property of GAD67 (the active enzyme is a homodimer); identical protein binding is the appropriate specific MF term. Supporting Evidence: file:human/GAD1/GAD1-uniprot.txt Homodimer. |
| GO:0005886 plasma membrane | TAS Reactome:R-HSA-888589 | MARK AS OVER ANNOTATED | Summary: Reactome (TAS) localization to the plasma membrane, derived from a GABA-release-at-the-synapse pathway context. GAD67 is a soluble cytosolic enzyme and does not itself reside in the plasma membrane. Reason: This localization reflects the pathway/reaction context (synaptic GABA release) rather than the intrinsic subcellular location of GAD67, which is cytosolic. Unlike the palmitoylated paralog GAD65, GAD67 has no membrane-targeting features. Supporting Evidence: file:human/GAD1/GAD1-uniprot.txt Belongs to the group II decarboxylase family |
| GO:0061202 clathrin-sculpted gamma-aminobutyric acid transport vesicle membrane | TAS Reactome:R-HSA-888572 | MARK AS OVER ANNOTATED | Summary: Reactome (TAS) localization to the clathrin-sculpted GABA transport vesicle membrane, a GABA-synthesis/vesicle-loading pathway context. GAD67 is a soluble cytosolic enzyme rather than an integral/peripheral vesicle-membrane protein. Reason: Pathway-context localization; the membrane association is characteristic of the palmitoylated GAD65 isoform, whereas GAD67 acts in the cytosol. Overstates GAD67's own subcellular location. Supporting Evidence: file:human/GAD1/GAD1-uniprot.txt Belongs to the group II decarboxylase family |
| GO:0061202 clathrin-sculpted gamma-aminobutyric acid transport vesicle membrane | TAS Reactome:R-HSA-888577 | MARK AS OVER ANNOTATED | Summary: Reactome (TAS) localization to the clathrin-sculpted GABA transport vesicle membrane (duplicate pathway-context annotation, from the GAD2 GABA-synthesis reaction). GAD67 is cytosolic. Reason: Same pathway-context over-localization as the other GO:0061202 annotations; this reaction is actually the GAD2 (GAD65) synthesis step. GAD67 itself is soluble cytosolic. Supporting Evidence: file:human/GAD1/GAD1-uniprot.txt Belongs to the group II decarboxylase family |
| GO:0061202 clathrin-sculpted gamma-aminobutyric acid transport vesicle membrane | TAS Reactome:R-HSA-888589 | MARK AS OVER ANNOTATED | Summary: Reactome (TAS) localization to the clathrin-sculpted GABA transport vesicle membrane (duplicate pathway-context annotation, from the GABA-release reaction). GAD67 is cytosolic. Reason: Duplicate pathway-context over-localization; GAD67 does not itself reside in the vesicle membrane. Supporting Evidence: file:human/GAD1/GAD1-uniprot.txt Belongs to the group II decarboxylase family |
| GO:0061202 clathrin-sculpted gamma-aminobutyric acid transport vesicle membrane | TAS Reactome:R-HSA-917744 | MARK AS OVER ANNOTATED | Summary: Reactome (TAS) localization to the clathrin-sculpted GABA transport vesicle membrane (duplicate pathway-context annotation, from the vesicle docking/priming reaction). GAD67 is cytosolic. Reason: Duplicate pathway-context over-localization; not an intrinsic location of soluble cytosolic GAD67. Supporting Evidence: file:human/GAD1/GAD1-uniprot.txt Belongs to the group II decarboxylase family |
| GO:0004351 glutamate decarboxylase activity | IDA PMID:10671565 Alternative splicing of GAD67 results in the synthesis of a ... | ACCEPT | Summary: Experimental (IDA) annotation to glutamate decarboxylase activity. This study establishes GAD67 enzymatic activity while characterizing a non-neural splice variant (GAD25/isoform 3) that lacks decarboxylase activity. Reason: Supports the core catalytic activity of full-length GAD67; the paper explicitly contrasts active GAD67 with the enzymatically inactive GAD25 isoform. Supporting Evidence: PMID:10671565 This transcript directs the synthesis of a protein without GAD |
| GO:0005515 protein binding | IPI PMID:10671565 Alternative splicing of GAD67 results in the synthesis of a ... | MARK AS OVER ANNOTATED | Summary: Bare protein binding (IPI) associated with the GAD25/GAD67 splice-variant study (interactant UniProtKB:Q05329). Uninformative generic MF term. Reason: The generic protein binding term conveys no specific molecular function; per curation guidelines it is over-annotated. Retained as a recorded interaction rather than removed, deferring to the curator's IPI. Supporting Evidence: PMID:10671565 a third form of |
| GO:0006538 L-glutamate catabolic process | TAS PMID:10671565 Alternative splicing of GAD67 results in the synthesis of a ... | ACCEPT | Summary: Author-statement (TAS) annotation to L-glutamate catabolic process. GAD67 consumes L-glutamate as substrate in the decarboxylation to GABA, so glutamate is catabolized in this reaction. Reason: Correct broader biological process - decarboxylation of L-glutamate is a glutamate catabolic step; complements the GABA biosynthetic process annotation by describing the fate of the substrate. Supporting Evidence: file:human/GAD1/GAD1-uniprot.txt L-glutamate + H(+) = 4-aminobutanoate + CO2 |
| GO:0012506 vesicle membrane | NAS PMID:10671565 Alternative splicing of GAD67 results in the synthesis of a ... | MARK AS OVER ANNOTATED | Summary: Non-traceable author statement (NAS) localizing GAD to the vesicle membrane. GAD67 is a soluble cytosolic enzyme; membrane/vesicle association is a property of the palmitoylated GAD65 isoform rather than GAD67. Reason: NAS localization that overstates GAD67's subcellular location; GAD67 has no membrane-anchoring modifications and acts in the cytosol. Kept (not removed) but flagged as an over-annotation of the intrinsic location. Supporting Evidence: file:human/GAD1/GAD1-uniprot.txt Belongs to the group II decarboxylase family |
| GO:0006540 GABA shunt | TAS PMID:1549570 Two human glutamate decarboxylases, 65-kDa GAD and 67-kDa GA... | KEEP AS NON CORE | Summary: Author-statement (TAS) annotation to the GABA shunt from the cDNA-cloning paper that established the two human GAD genes and their enzymatic activity. Reason: GAD1 catalyzes the entry step of the GABA shunt; retained as a non-core metabolic-context process (core process is GABA biosynthesis). The cited paper confirms both GADs encode enzymatically active decarboxylases. Supporting Evidence: PMID:1549570 Both cDNAs direct the synthesis of enzymatically active GADs in |
| GO:0007268 chemical synaptic transmission | TAS PMID:8954991 Mice lacking the 65 kDa isoform of glutamic acid decarboxyla... | KEEP AS NON CORE | Summary: Author-statement (TAS) annotation to chemical synaptic transmission. GAD67 contributes to inhibitory neurotransmission indirectly by supplying GABA; the cited GAD65-knockout study shows GAD67 maintains brain GABA levels and its loss relates to seizure susceptibility. Reason: Synaptic transmission is a downstream physiological consequence of GAD1's GABA-synthesizing activity rather than its own molecular action; kept as a non-core process annotation. Supporting Evidence: PMID:8954991 levels of mRNA and protein were largely unchanged by the GAD65 mutation. |
| GO:0005829 cytosol | IBA GO_REF:0000033 | NEW | Summary: Proposed specific cytosolic localization for GAD67. GAD67 is a soluble cytosolic enzyme lacking the membrane-targeting modifications of GAD65; cytosol is the compartment where its constitutive GABA synthesis occurs, refining the existing cytoplasm (GO:0005737) IBA annotation. Reason: Added to record the specific cytosolic location used in core_functions; it refines the existing cytoplasm IBA annotation to the compartment in which soluble GAD67 acts. Supporting Evidence: file:human/GAD1/GAD1-uniprot.txt Belongs to the group II decarboxylase family |
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Download this section (compressed HTML)Q: To what extent is GAD67 (versus GAD65) responsible for the pool of GABA that supports phasic synaptic inhibition rather than only tonic/basal GABA, and does GAD67 have a physiologically meaningful presence at the presynaptic active zone in human neurons?
Q: Which of the reported GAD1 disease phenotypes (developmental and epileptic encephalopathy vs spastic cerebral palsy / spastic paraplegia) are robustly attributable to GAD1 loss of function, given that one cerebral-palsy pedigree was later reattributed to HPDL?
Experiment: Fractionation and imaging of endogenous GAD67 in human GABAergic neurons to quantify the cytosolic versus membrane/vesicle-associated pools and directly test the Reactome-derived vesicle-membrane localization annotations.
Experiment: Enzyme kinetics and thermal/holo-apo stability comparison of recombinant wild-type GAD67 versus disease-associated variants (e.g. DEE89 alleles) to link specific mutations to loss of decarboxylase activity and PLP cofactor binding.
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