GLDP1 (At4g33010, UniProt Q94B78) - curation notes

Deep research could not be run in this environment (no provider API keys). These notes
are a manual literature summary built only from cached publications (publications/PMID_*.md)
and the UniProt record (GLDP1-uniprot.txt). No -deep-research-*.md file exists for this gene.

Identity

• Glycine dehydrogenase (decarboxylating) 1, mitochondrial; the P protein of the glycine
  decarboxylase complex (GDC; glycine cleavage system). EC 1.4.4.2, PLP-dependent, GcvP family
  (PANTHER PTHR11773:SF1). Mitochondrial transit peptide 1-67; PLP-lysine at K774 (by similarity).
• Arabidopsis has two P-protein genes, At4g33010 (GLDP1) and At2g26080 (GLDP2)
  PMID:22303256.

Molecular function

• The P protein is the decarboxylating enzyme of GDC: PMID:22303256. The aminomethyl remainder goes to the H protein:
  PMID:22303256.
• UniProt curated function [file:ARATH/GLDP1/GLDP1-uniprot.txt "The P protein binds the alpha-amino
  group of glycine through its pyridoxal phosphate cofactor"]; reaction RHEA:24304.
• Both GLDP isoforms have catalytic activity, GLDP2 weaker PMID:33506579 (abstract only). GLDPs form homo- and heterodimers
  PMID:33506579.
• Redox regulation: GDC is inhibited by S-nitrosylation/glutathionylation; GLDP1 Cys residues
  identified PMID:20089767 (abstract only; site list from
  UniProt).

Complex and location

• GDC = P, H, T, L proteins; all four needed for activity PMID:17496108.
• Arabidopsis leaf GDC stoichiometry by MS includes both P isoforms, P1 being ~4x P2
  PMID:32311173 (abstract only).
• Mitochondrial: UniProt location experimental [PubMed:14671022]; plant GDC is a matrix complex
  PMID:11286922. Detected in mitochondria isolated for ICP55
  study PMID:25862457.
• Plastid, cytosol, plasma membrane and apoplast detections (HDA) come from bulk proteomics of
  fractions known to carry contaminants; e.g. the chloroplast stroma study estimated
  PMID:18431481. Treated as contaminants of an abundant leaf mitochondrial matrix protein.

Biological role

• GDC + SHMT form the mitochondrial part of photorespiration PMID:22303256.
• Genetics PMID:17496108: single gldp1 or gldp2 knockouts are near wild type
  ["The individual knockout of either of these two genes does not significantly alter metabolism and
  photosynthetic performance indicating functional redundancy"], but gldp1 mutants accumulate
  glycine under photorespiratory conditions ["which were significantly elevated under
  photorespiratory conditions"], and ["AtGLDP1 clearly carries a somewhat higher photorespiratory
  workload than AtGLDP2"]. The double mutant arrests at the cotyledon stage even in high CO2,
  indicating GDC is indispensable for one-carbon metabolism, not only photorespiration
  ["provides evidence for the nonreplaceable function of GDC in vital metabolic processes other than
  photorespiration"].
• Expression: PMID:17496108.

Annotation decisions (summary)

• Core: GO:0004375 (MF), GO:0019464 / GO:0006546 (BP), mitochondrion. NEW: GO:0005960 glycine
  cleavage complex (PMID:32311173) and GO:0009853 photorespiration (PMID:17496108).
• Photorespiration comparator check (QuickGO, 2026-10): other Arabidopsis enzymes catalysing C2-cycle
  steps carry GO:0009853 (SHM1 IMP, GLYK IMP/IBA, HPR TAS, GGAT1 TAS, PLGG1 IMP); the GDC subunits
  (GLDP1/2, GDCH, GDCST) lack it. GLDP1 catalyses a step of the cycle, so it passes the participation
  test.
• mRNA binding (RNA interactome capture, no follow-up): over-annotated. Protein binding to 14-3-3
  (TAP-MS): removed per protein-binding policy. Response to cadmium (IEP proteomics): non-core.
• The retracted iNOS claim (UniProt CAUTION, PubMed:12757708 retracted by 15599984) is not used.