GLDC

GLDC encodes glycine decarboxylase, the P-protein subunit of the mitochondrial glycine cleavage system (GCS), which degrades glycine and supplies glycine-derived one-carbon units to folate metabolism (PMID:10798358, PMID:38761651). Loss-of-function GLDC mutations abolish GCS activity and cause non-ketotic hyperglycinemia (NKH), with mutations in GLDC accounting for the large majority of cases; disease-causing alleles act through diverse mechanisms including large deletions, missense substitutions at the cofactor-binding hotspot Lys754, splicing defects, and loss of translation initiation, and residual enzymatic activity tracks closely with clinical severity (PMID:16450403, PMID:15236413, PMID:15864413, PMID:28244183). Functional rescue confirms the metabolic requirement: AAV9-mediated GLDC delivery restores hepatic and brain GLDC expression, lowers plasma and brain glycine, and normalizes folate one-carbon and betaine/choline profiles in deficient mice, and rescues the lethal phenotype in humanized NKH models [PMID:38761651, PMID:bio_10.1101_2025.03.26.645560]. Beyond systemic glycine balance, GLDC controls extracellular glycine availability in the dentate gyrus, where GLDC copy-number gain depletes glycine, suppresses LTP at medial perforant path–dentate gyrus synapses, and produces schizophrenia-like behavioral deficits reversible by glycine supplementation—implicating GLDC-mediated glycine catabolism in NMDA receptor co-agonist availability and synaptic plasticity (PMID:39210012, PMID:41361932). GLDC additionally restrains antiviral innate immunity, with its inhibition or depletion amplifying IFNβ/ISG responses and suppressing influenza replication in vivo (PMID:30498026). In cancer and ischemic injury contexts GLDC is subject to post-translational regulation—K514 acetylation drives a VPS34/Beclin1/ATG14 interaction promoting autophagy, and EGFR–SRC–FBXL3–dependent K63-linked polyubiquitination of K636 directs nuclear GLDC to repress STAT1-driven MHC-I transcription and enable immune evasion—and it modulates Hippo/EMT, aerobic glycolysis, Akt/NF-κB, and UCP1-dependent stress responses in a tissue-dependent manner (PMID:41550650, PMID:41728086, PMID:37781511).

1. 2000 Medium

   Establishing GLDC's genomic structure, tissue expression, and that homozygous deletion abolishes glycine cleavage activity defined GLDC as the genetic basis of the P-protein deficiency form of NKH.

   Evidence RNA blotting, primer extension, and PCR with pseudogene-controlled assays in human tissues

   PMID:10798358

   Open questions at the time

   • Pseudogene homology complicates expression quantification
   • Did not resolve the catalytic mechanism of the P-protein
2. 2006 High

   Comprehensive mutation screening across NKH families established GLDC as the major causative gene and located a functional cofactor-binding hotspot at Lys754, linking specific residues to enzyme function.

   Evidence Sequencing of all 25 exons in 69 NKH families with haplotype analysis

   PMID:16450403

   Open questions at the time

   • Does not establish how each variant affects catalysis versus stability
   • Founder deletion origins inferred from haplotype, not functional assay
3. 2006 Medium

   Genotype-phenotype correlations from enzyme activity assays showed that residual GCS activity (e.g. 32% for A802V vs 2.6% for Y161C) determines clinical severity, including prenatal glycine accumulation.

   Evidence GCS enzyme activity assays in patient placental tissue with CSF/plasma glycine measurement

   PMID:15236413 PMID:16404748

   Open questions at the time

   • Activity measured in limited tissues
   • Quantitative threshold for symptom onset not generalized
4. 2017 Medium

   Functional expression of missense variants revealed that many GLDC loss-of-function alleles act through protein instability rather than direct catalytic disruption, refining how variants cause disease.

   Evidence Expression of 19 variants in COS7 cells with enzymatic assay, Western blot, and 3D structural modeling

   PMID:28244183

   Open questions at the time

   • No experimentally solved human GLDC structure
   • Stability assessed in heterologous cells, not patient mitochondria
5. 2019 High

   Reciprocal gain/loss-of-function work uncovered a non-metabolic role: GLDC negatively regulates antiviral innate immunity, restraining IFNβ/ISG induction and permitting viral replication.

   Evidence siRNA, AOAA inhibition, and overexpression with IFNβ/ISG and viral replication readouts plus in vivo influenza model

   PMID:30498026

   Open questions at the time

   • Molecular link between glycine catabolism and IFN signaling not defined
   • Whether enzymatic activity per se is required is unresolved
6. 2024 High

   Gene-replacement and copy-number models established causality in both directions for glycine homeostasis: GLDC restoration lowers glycine and normalizes one-carbon metabolism, while GLDC gain depletes dentate gyrus glycine and impairs synaptic plasticity and behavior.

   Evidence AAV9 GLDC gene therapy with metabolite profiling, and chromosome-engineered allelic series with FRET glycine imaging, LTP electrophysiology, and behavior

   PMID:38761651 PMID:39210012

   Open questions at the time

   • Cell-type-specific contributions to brain glycine pool not dissected
   • Link from synaptic glycine to specific NMDA receptor populations inferred
7. 2025 Medium

   Glycine supplementation rescued behavioral deficits in Gldc copy-number mice, confirming that GLDC-mediated glycine catabolism is mechanistically responsible for NMDA co-agonist depletion phenotypes.

   Evidence Chronic oral glycine supplementation with behavioral battery and spine density in Gldc 4-copy mice

   PMID:41361932

   Open questions at the time

   • Single lab
   • Does not pinpoint the receptor subtype or circuit mediating rescue
8. 2025 Medium

   Post-translational regulation of GLDC was defined: K514 acetylation drives a VPS34/Beclin1/ATG14 interaction inducing autophagy and suppressing EMT in HCC.

   Evidence Co-IP, VPS34/Beclin1/ATG14 pulldown, K514R acetylation-dead mutant, and in vitro/in vivo tumor assays

   PMID:41550650

   Open questions at the time

   • Acetyltransferase responsible for K514 not identified here
   • Whether autophagy role requires catalytic activity unknown
9. 2026 Medium

   An EGFR–SRC–FBXL3 axis was shown to K63-polyubiquitinate GLDC at K636, directing nuclear GLDC to repress STAT1-driven MHC-I transcription and enable immune evasion, defining a druggable signaling node.

   Evidence K63-linkage ubiquitination assays, multiple Co-IPs, FBXL3 Y306 phosphorylation analysis, K636R mutants, MHC-I/CD8+ T cell assays, and in vivo SRC inhibitor + anti-PD-1

   PMID:41728086

   Open questions at the time

   • Nuclear localization mechanism of GLDC not detailed
   • Single lab, reciprocal validation across models pending
10. 2023 Medium

    Context-dependent cancer roles emerged: GLDC inhibits Hippo signaling to drive colorectal metastasis/EMT and, via enzyme activity under HIF1-α control, enhances aerobic glycolysis in prostate cancer.

    Evidence Hippo inhibitor (Verteporfin) rescue with tail-vein metastasis, and metabolomics with glucose/lactate/LDH assays and HIF1-α regulation analysis

    PMID:37668829 PMID:37781511

    Open questions at the time

    • Direction of GLDC effect differs across tumor types, mechanism of context-dependence unresolved
    • Direct molecular link to Hippo components not established

• It remains unresolved how GLDC's mitochondrial enzymatic function is mechanistically connected to its diverse non-canonical roles in innate immunity, autophagy, MHC-I transcription, and stress signaling, and whether these require catalytic activity, glycine flux, or moonlighting protein interactions.
• No unifying mechanism linking metabolic and signaling functions
• Catalytic dependence of non-metabolic roles untested in most contexts
• Subcellular pool (mitochondrial vs nuclear) driving each function not delineated