mtLPD1 (At1g48030, UniProt Q9M5K3) - 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 the cached
publications in publications/, the UniProt record (mtLPD1-uniprot.txt) and
PubMed searches. No -deep-research-*.md file exists for this gene.

Identity and naming caution

• UniProt Q9M5K3 (DLDH1_ARATH), "Dihydrolipoyl dehydrogenase 1, mitochondrial"
  (AtmLPD1, mtLPD1), EC 1.8.1.4; gene LPD1, locus At1g48030. AltName "Glycine
  cleavage system L protein 1".
• The folder is named mtLPD1 because the symbol LPD1 is also used for the
  plastid E3 proteins (ptLPD1/ptLPD2). Everything here is about the
  mitochondrial At1g48030 protein.
• Mitochondrial paralog: mtLPD2, At3g17240 (UniProt Q9M5K2); reviewed in
  genes/ARATH/mtLPD2/. The two share 94% identity
  PMID:11743115.
• In the Rostock (Bauwe/Timm) nomenclature, mtLPD1 is GDC-L1
  PMID:31413204. The
  "GCS-L1" of the Wittmiss et al. 2020 stoichiometry paper (same group) is taken
  to be the same protein; the cached abstract does not give the locus.
• Mitochondrial transit peptide 1..36 (cleavage after Phe-36 determined
  experimentally, UniProt ECO:0000269 PubMed:25732537, 25862457); class-I
  pyridine nucleotide-disulfide oxidoreductase family; FAD/NAD binding sites and
  redox-active disulfide 82-87 (by similarity).

Biochemical function

• Dihydrolipoyl dehydrogenase (E3, L protein): reoxidizes protein-bound
  dihydrolipoamide using NAD+ via FAD (UniProt CATALYTIC ACTIVITY, RHEA:15045)
  PMID:22303256.
• Direct biochemistry on the Arabidopsis protein: recombinant mtLPD1 was
  characterized and is inhibited by NADH and redox-regulated by thioredoxins
  (abstract only)
  PMID:38518065.
  A methods chapter describes expression, purification, activity and redox
  regulation of plant mtLPD1 (abstract only) PMID:38861078.
• Note: the recombinant L protein in the TRXo1 paper (PMID:31413204) was the pea
  enzyme (PsmtLPD), not At1g48030.

Multienzyme complexes served

• Mitochondrial E3 is shared by four complexes: GDC, pyruvate dehydrogenase,
  2-oxoglutarate dehydrogenase and branched-chain 2-oxoacid dehydrogenase
  PMID:38861078.
• Leaf GDC stoichiometry by MS (abstract only): the Arabidopsis leaf complex
  contains four times more L1 than L2
  PMID:32311173.
  This is the most direct protein-level evidence that mtLPD1 is the main leaf GDC
  L protein.
• In non-photosynthetic cell-culture mitochondria, both proteins were identified
  but mtLPD2 was more abundant (AAF34795 is the mtLPD1 cDNA, EMBL AF228639)
  PMID:11743115.

Expression

• mtLPD1 mRNA is high in green leaves and low in roots, and strongly
  light-induced; mtLPD2 shows the inverse organ pattern (abstract only)
  PMID:11598235
  PMID:11598235.
• From this the authors hypothesized the division of labour, while assuming
  interchangeability in the matrix
  PMID:11598235
  PMID:11598235.
  The 2001 paper characterized only an mtlpd2 knockout, not an mtlpd1 mutant.

Genetic evidence for photorespiration

• Liu et al. 2026 (abstract only; no PMC full text) characterized loss-of-function
  mutants for both mtLPDs: mtLPD1 has the predominant role in photorespiration,
  the two are largely redundant for BCAA degradation in carbon starvation, and
  both act dose-dependently in gametophyte development
  PMID:41990722
  PMID:41990722
  PMID:41990722.
  Allele identities, the high-light assay and whether gametophyte defects require
  combined loss cannot be checked from the abstract.
• Overexpression of the GDC L protein (Timm et al. 2015; abstract only) increased
  CO2 assimilation, photorespiration and growth
  PMID:26116608.
  The 2015 abstract does not name the transgene. The 2025 follow-up calls the lines
  mtLPD1 overexpressors, but designates them "PsL-L2 and PsL-L3"
  PMID:40032651,
  which suggests (not verified here) a pea L-protein transgene. Gain-of-function
  data therefore show that L-protein activity limits photorespiratory flux, but
  are not evidence about the endogenous At1g48030 gene specifically.
• Thioredoxin o1/h2 mutants: metabolite patterns point at mtLPD1-dependent
  pathways (PMID:38518065).

Localization

• Mitochondrial matrix (UniProt, ECO:0000269 PubMed:14671022). Found in
  mitochondrial proteomes (PMID:11743115, 14671022, 17137349, 18385124, 22923678,
  25293756).
• Complex I (IDA, PMID:20197505): the authors list lipoamide dehydrogenase among
  contaminants of their complex I preparation
  PMID:20197505.
• NOT Golgi (RCA, PMID:22430844): consistent with matrix location.
• Nucleus (HDA, PMID:28887381) and apoplast (HDA, PMID:18538804): single
  high-throughput hits for a matrix protein; treated as over-annotations per
  projects/ARATH/organelle-audit.md.

Ligand-affinity proteomics

• Cu/Zn/Co IMAC (PMID:20018591) and immobilized-ATP capture (PMID:17137349): not
  physiological ligands of LPD (FAD and NAD+ are). Same treatment as mtLPD2.

Stress responses

• Cadmium (IEP, PMID:20005002): leaf 2D-gel proteome; abstract only, and the
  abstract does not name the LPD spot or say how the 94%-identical paralogs were
  distinguished. Not verifiable here.

Comparator check for GDC/photorespiration terms (QuickGO, 2026-10-20)

• GO:0009853 photorespiration in Arabidopsis is carried by other C2-cycle
  enzymes (SHM1, GLYK, HPR, GGAT1, PLGG1...) but by no GDC subunit in GOA; the
  sibling reviews GLDP1, GLDP2, GDCST and GDCH each added NEW photorespiration.
• L proteins in other species do carry GCS terms: pea mitochondrial LPD P31023
  has GO:0005960 glycine cleavage complex (IDA) and GO:0019464 (IDA); yeast LPD1
  P09624 has GO:0005960 (IMP), GO:0006546 (IMP) and GO:0019464 (RCA). So no
  convention excludes the shared E3 from GCS annotations.
• Participation: the L protein catalyses the last step of the GCS cycle
  (reoxidation of the H-protein dihydrolipoyl arm), so it does part of the work
  of glycine decarboxylation and hence of photorespiration.

Module cross-check

• modules/photorespiration_c2_cycle.yaml says "The leaf L protein is mainly
  mitochondrial LPD1 (mtLPD1, At1g48030, UniProtKB:Q9M5K3)". Supported by: leaf
  GDC stoichiometry (L1 4x L2, PMID:32311173, isoform mapping by group
  nomenclature), leaf-enriched and light-induced expression (PMID:11598235), and
  the mutant analysis showing mtLPD1 predominant in photorespiration
  (PMID:41990722). Both proteins are in the complex, so "mainly" is the right word.
  The module currently cites only the expression hypothesis (PMID:11598235) and
  the methods-chapter statement (PMID:38861078); PMID:32311173 and PMID:41990722
  are stronger evidence that could be added there.
• modules/glycine_cleavage_system.yaml L-protein role uses GO:0004148 with
  non-plant representatives; consistent with the MF here.