HPR2 (At1g79870, Q9CA90) curation notes

Deep research could not be run in this environment (no provider API keys). These notes
are built only from cached publications (publications/PMID_*.md) and the UniProt record
(HPR2-uniprot.txt). No -deep-research-*.md file exists for this gene.

Identity and family

• Glyoxylate/hydroxypyruvate reductase A HPR2; 313 aa; D-isomer specific 2-hydroxyacid
  dehydrogenase family, GyaR subfamily (UniProt SIMILARITY, ECO:0000305; Pfam PF00389/PF02826;
  PANTHER PTHR10996:SF178).
• Also named HPPR2 (hydroxyphenylpyruvate reductase 2) in the tyrosine-pathway literature
  PMID:30233632.

Enzymatic activity

• Purified from hpr1 knockout leaves as the NADPH-dependent HPR activity; identified as
  At1g79870 by MS and cross-reaction with anti-spinach HPR2 serum PMID:18952776.
• Recombinant enzyme prefers NADPH and hydroxypyruvate; NADH rates ~4x lower; glyoxylate
  also reduced PMID:18952776
  PMID:18952776.
• Strongly inhibited by oxalate (UniProt ACTIVITY REGULATION, ECO:0000269 PubMed:18952776).
• Also reduces 4-hydroxyphenylpyruvate (pHPP) to 4-hydroxyphenyllactate (pHPL), but its highest
  catalytic efficiency is with hydroxypyruvate PMID:30233632.

Localization

• Cytosolic. GFP-HPR2 showed no organelle targeting PMID:18952776;
  independent GFP study in protoplasts PMID:30233632.
• A mitochondrion HDA call (membrane-fraction SEC profiling, PMID:28887381) is not supported
  by any targeting data; the same study notes extensive cytosol/membrane partitioning.

Physiological role

• Cytosolic bypass of peroxisomal HPR1 in photorespiration PMID:18952776.
• hpr2 single mutants nearly wild-type; hpr1 hpr2 double mutants air-sensitive and rescued
  by 1% CO2 PMID:18952776.
• HPR1 dominant; HPR2 an overflow route PMID:22303256.
• A third enzyme HPR3 adds further redundancy PMID:21205613.
• Secondary role in tyrosine-derived pHPL formation PMID:30233632.

Other

• Salicylic acid binding: HPR2 bound SA in two in vitro assays (SPR with 3AESA; SA-competable
  4AzSA crosslinking) PMID:25628632.
  No effect of SA on HPR2 activity or physiological significance was reported.

Curation decisions (summary)

• Core MF: hydroxypyruvate reductase [NAD(P)H] activity (GO:0016618), NADPH preferred
  (GO:0120509 also accepted). Glyoxylate reductase (NADPH) and HPPR activity kept as non-core.
• Core BP: oxidative photosynthetic carbon pathway (GO:0009854, part_of photorespiration).
• Core CC: cytosol. Cytoplasm rows modified to cytosol; mitochondrion HDA marked over-annotated.
• SA binding kept as non-core (in vitro only).