DHODH (human, UniProtKB:Q02127) — review notes

Reviewed GO annotations for human DHODH — dihydroorotate dehydrogenase (quinone),
mitochondrial (EC 1.3.5.2; PYRD_HUMAN). Grounded in the cached UniProt record
(DHODH-uniprot.txt), the seeded GOA (DHODH-goa.tsv), cached publications/PMID_*.md,
cached Reactome entries, and the pre-existing DHODH-deep-research-falcon.md (generated
2025-12-27; falcon is currently out of credits so no new deep-research run was made).

Verified biology

• Class 2 (type 2) flavoenzyme; catalyses the 4th and only mitochondrial step of de
  novo pyrimidine biosynthesis: FMN-dependent oxidation of (S)-dihydroorotate → orotate,
  passing electrons to ubiquinone [file:human/DHODH/DHODH-uniprot.txt "Reaction=(S)-dihydroorotate + a quinone = orotate + a quinol"; EC=1.3.5.2].
• Cofactor FMN, 1 per subunit [file:... "Name=FMN; Xref=ChEBI:CHEBI:58210"; PMID:10673429].
• Kinetics of recombinant human enzyme: Km 4 µM (DHO), 9.9 µM (ubiquinone-50)
  PMID:8925840.
• Mitochondrion inner membrane, single-pass; catalytic TIM-barrel domain faces the
  intermembrane space; N-terminal helices form the lipophilic ubiquinone/inhibitor tunnel
  [file:... "Mitochondrion inner membrane"; PMID:10673429 "an alpha-helical domain that forms the opening of a tunnel"].
• Disease: Postaxial acrofacial dysostosis / Miller syndrome (MIM:263750), biallelic
  loss-of-function [PMID:19915526 via UniProt DISEASE].
• Drug target: leflunomide/teriflunomide (A77 1726, IC50 ~1 µM), brequinar
  PMID:8925840.
• Ferroptosis: DHODH reduces ubiquinone to ubiquinol in the IMM as a parallel
  (GPX4/FSP1-independent) radical-trapping antioxidant defence PMID:33981038.

Curation decisions of note

• GO:0004151 dihydroorotase activity (IEA, GO_REF:0000107 Ensembl Compara) → REMOVE.
  This is a different enzyme (EC 3.5.2.3, the DHO domain of trifunctional CAD, step 3 of
  the pathway). DHODH is EC 1.3.5.2 (step 4). Clearly-wrong orthology-transfer IEA (mouse
  ortholog O35435 mis-mapped). Endorsed by task brief.
• GO:0005737 cytoplasm (IEA, InterPro IPR005720) → REMOVE. Domain-based electronic
  inference mislocalising a strictly IMM-anchored protein whose catalytic domain faces the
  intermembrane space. (HPA reports a cytosol IDA in the UniProt DR block, but that is not
  in the GOA TSV under review.)
• GO:0005515 protein binding (IPI ×2, PMID:32296183 HuRI) → both MARK_AS_OVER_ANNOTATED
  (NOT removed, per curation policy for bare protein-binding IPIs). WITH/FROM P49638 (TTPA)
  and Q6ZMZ0 (RNF19B); both are single high-throughput Y2H interactions, uninformative and
  unvalidated. The seeded review only had one GO:0005515 entry; added the second GOA row.
• Generic parents (GO:0016020 membrane, GO:0016491 oxidoreductase activity, GO:0016627
  oxidoreductase acting on CH-CH) → MARK_AS_OVER_ANNOTATED (more specific terms present).
• NEW annotations added (not in GOA): GO:0010181 FMN binding (structural + fluorimetric
  evidence), GO:0048038 quinone binding (ubiquinone tunnel), GO:0110076 negative regulation
  of ferroptosis (Mao et al. 2021 Nature).

Reference-format housekeeping

• Converted all UniProt supporting_text from reference_id: UniProt:Q02127 to the
  file:human/DHODH/DHODH-uniprot.txt convention and added a matching top-level references
  entry. Trimmed four UniProt quotes that had combined non-adjacent CC lines so each is
  now a genuine verbatim substring of the record.
• All PMID/DOI supporting_text verified verbatim (whitespace-normalized) against cached
  publications. Reactome titles left exactly as fetched.

Final: just validate human DHODH → ✓ Valid.