GLS (human) — review notes

UniProt: O94925 (GLSK_HUMAN), "Glutaminase kidney isoform, mitochondrial"; gene GLS (syn. GLS1, KIAA0838); 669 aa precursor. HGNC:4331. EC 3.5.1.2.

Identity and core biochemistry

GLS is the kidney-type / phosphate-activated glutaminase. Two catalytically active isoforms exist by alternative splicing: KGA (isoform 1, O94925-1) and GAC / Glutaminase C (isoform 3, O94925-3); a third splice product GAM (isoform 2, O94925-2) lacks catalytic activity.
- Catalytic reaction (UniProt CATALYTIC ACTIVITY): [file:human/GLS/GLS-uniprot.txt "Reaction=L-glutamine + H2O = L-glutamate + NH4(+)"]; EC=3.5.1.2; Rhea:RHEA:15889.
- FUNCTION (UniProt): [file:human/GLS/GLS-uniprot.txt "Catalyzes the first reaction in the primary pathway for the"] renal catabolism of glutamine; plays a role in maintaining acid-base homeostasis; regulates the levels of the neurotransmitter glutamate.
- Isoform 2 (GAM): [file:human/GLS/GLS-uniprot.txt "Lacks catalytic activity."]
- PMID:22049910
- PMID:24451979 — feeds glutamate into the TCA cycle (glutaminolysis/anaplerosis).
- PMID:11015561 and the catalytically inactive hGAM is muscle-specific.

Subcellular location

Mitochondrion; the mature enzyme is generated from a ~74-kDa cytosolic precursor imported and processed by the mitochondrial-processing peptidase (MPP) to 68-/65-kDa matrix chains.
- [file:human/GLS/GLS-uniprot.txt "The 74-kDa cytosolic precursor is"] translocated into the mitochondria and processed... to yield the mature 68- and 65-kDa subunits.
- Matrix chains: [file:human/GLS/GLS-uniprot.txt "Mitochondrion matrix {ECO:0000250|UniProtKB:P13264}."]
- GAC is distinctly mitochondrial: PMID:22228304.
- Brain GA cDNA encodes a protein with an N-terminal mitochondrial targeting signal: PMID:10719215.
- KGA can be relocalised from mitochondria to neurite terminals by ATCAY/Caytaxin: PMID:16899818.
- The cytosol annotation (GO:0005829, IEA UniProtKB-SubCell) reflects the cytosolic precursor stage of isoform 1 before mitochondrial import ([file:human/GLS/GLS-uniprot.txt "Cytoplasm, cytosol"]); it is a real but non-core, transient localization.

Quaternary structure / regulation

• Homotetramer, dimer of dimers (UniProt SUBUNIT, citing PubMed:22538822, 26988803, 28526749, 29317493). Tetramerization is coupled to activation.
• Phosphate-activated; BPTES/CB-839-class allosteric inhibitors bind at the dimer interface and lock a nonproductive tetramer.
• PMID:22049910
• Phosphate activation / tetramerization: [PMID:22228304 "the \ntetramerization-induced lifting of a \"gating loop\" as essential for the \nphosphate-dependent activation process"].
• Active-site catalytic residues (KGA numbering): catalytic nucleophile Ser286, Lys289 general base, Tyr466; substrate/active-site residues Tyr249, Asn335, Glu381, Asn388, Tyr414, Val484 (PMID:24451979). DON covalently modifies Ser286.
• KGA activity is stimulated by EGF/Raf-Mek-Erk phosphorylation and the enzyme associates with RAF1/MAP2K2 (PMID:22538822); interacts with ATCAY (Caytaxin), which relocalises it and reduces its activity (PMID:16899818).
• C-terminal ANK repeats: PMID:28526749 — glutaminase ANK repeats fold via intramolecular contacts that occlude the usual ANK protein-protein-interaction surface and limit assembly into supra-tetrameric filaments.

Biological roles

• Glutaminolysis / anaplerosis: first, committed step feeding glutamate to TCA (via GLUD1/transaminases -> alpha-ketoglutarate). Central to cancer "glutamine addiction"; drug target (CB-839/telaglenastat, BPTES).
• PMID:29317493
• Renal ammoniagenesis / acid-base homeostasis (UniProt FUNCTION).
• Brain glutamate-glutamine cycle: supplies neurotransmitter glutamate.
• PMID:16899818
• Intracellular glutamate homeostasis: gain-of-function Ser482Cys causes hyperactivity, increased glutamate/decreased glutamine.
• PMID:30239721; "we describe an inborn error of glutamate metabolism caused by a GLS hyperactivity variant".

Disease

• DEE71 (developmental & epileptic encephalopathy 71; MIM 618328): autosomal recessive, loss-of-function (UniProt DISEASE; PubMed:30575854).
• CASGID (cataract, subcutaneous nodules, glutamate excess, developmental delay; MIM 618339): autosomal dominant, gain-of-function Ser482Cys (PMID:30239721).
• GDPAG (global developmental delay, progressive ataxia, elevated glutamine; MIM 618412): autosomal recessive, GAG/short-tandem-repeat expansion loss-of-function (UniProt DISEASE; PubMed:30970188).

Annotation review judgments (summary)

• Core MF: glutaminase activity (GO:0004359) — strongly supported by multiple EXP/IDA structural-enzymology papers and UniProt catalytic activity. ACCEPT.
• Core BP: L-glutamine catabolic process (GO:0006543) and L-glutamate biosynthetic process (GO:0097054) — the two faces of the same reaction; both directly supported (IDA PMID:22049910). ACCEPT.
• Location: mitochondrion (GO:0005739) core; mitochondrial matrix (GO:0005759) the specific matrix location of the mature chains. ACCEPT.
• protein homotetramerization (GO:0051289) — real quaternary-structure property (dimer of dimers); KEEP_AS_NON_CORE (structural, not the pathway function).
• intracellular glutamate homeostasis (GO:0090461) IMP PMID:30239721 — supported by the gain-of-function disease study; ACCEPT (organism-level consequence of the MF).
• negative regulation of L-glutamine biosynthetic process (GO:0062133) IDA PMID:16899818 — the paper shows ATCAY/Caytaxin inhibits KGA and reduces glutamate; it is not evidence that GLS negatively regulates glutamine biosynthesis. This BP term is a poor fit for GLS's own activity (glutamine catabolism, not regulation of glutamine synthesis). MARK_AS_OVER_ANNOTATED (experimental IDA — do not REMOVE).
• protein binding (GO:0005515) IPI PMID:16899818 with ATCAY (Q86WG3) — bare protein binding; keep as evidence of the direct ATCAY interaction but MARK_AS_OVER_ANNOTATED (uninformative MF); the biology is captured in notes/core.
• IEA/IBA/ISS/NAS/TAS/HTP duplicates of the above accepted terms: ACCEPT or KEEP_AS_NON_CORE per redundancy.
• amino acid metabolic process (GO:0006520) IEA (ARBA) and L-glutamine metabolic process (GO:0006541) IEA (InterPro) — correct but general parents of the specific catabolic term; KEEP_AS_NON_CORE / MODIFY toward the specific GO:0006543.

2026-09: GO:0005515 rows re-actioned under the protein-binding policy

This section supersedes the earlier MARK_AS_OVER_ANNOTATED plan for protein binding written above. The repo policy excludes that action for GO:0005515. A row goes to MODIFY where the paper supports a more informative MF, and otherwise to REMOVE. Removal does not mean the interaction is false.
- PMID:16899818 (ATCAY/Caytaxin): REMOVE. GLS is the cargo and regulated partner of Caytaxin, and the paper supports no more specific GLS MF.