TAS1R3 (A0A7L3N407, Oreotrochilus melanogaster) - curation notes

Identity and record status

• UniProt A0A7L3N407, unreviewed (TrEMBL), 832 aa, Flags: Fragment, NON_TER at
  both residue 1 and 832. Derived from the Bird 10,000 Genomes (B10K) Project
  whole-genome shotgun assembly (ORF OREMEL_R00692, strain OUT-0002; Zhang G.,
  submitted Sep 2019).
• NCBI taxon id in the record is 689266 (Oreotrochilus melanogaster), per the
  OX line of TAS1R3-uniprot.txt. The seeded YAML stub had the wrong taxon id
  (NCBITaxon:8782, which is not this organism's id) - corrected to 689266
  during this review.
• gene_symbol in the seeded stub was set to the UniProt accession
  (A0A7L3N407) rather than the gene symbol - corrected to TAS1R3 (UniProt
  GN Name=Tas1r3).
• No gene-specific PMIDs were seeded for this record (fetch-gene-pmids found
  none); all 9 GOA rows are IEA (ARBA / InterPro2GO / TreeGrafter / UniProt
  combined pipelines), not experimental.

Key background biology (not species-specific evidence)

Baldwin et al. 2014 Science, PMID:25146290 (full text cached,
publications/PMID_25146290.md, PMC4302410):

• Most vertebrates have three T1Rs; TAS1R2-TAS1R3 mediates sweet taste and
  TAS1R1-TAS1R3 mediates umami taste. Birds (including chickens, turkeys,
  zebra finches, and swifts) generally lack TAS1R2 entirely
  PMID:25146290.
• In the hummingbird lineage specifically (studied via Anna's hummingbird,
  Calypte anna), the ancestral TAS1R1-TAS1R3 umami heterodimer was
  repurposed to detect carbohydrates instead of amino acids
  PMID:25146290.
• Neither TAS1R1 nor TAS1R3 alone gave a ligand response in heterologous
  cells - only the co-expressed heterodimer did
  PMID:25146290. This means TAS1R3 cannot sensibly be annotated as an
  independently-functional receptor; its molecular activity is always
  exercised as part of the TAS1R1-TAS1R3 dimer.
• Chicken/swift T1R1-T1R3 (which lack the hummingbird-specific
  substitutions) instead detect amino acids (alanine, serine), not sugars
  PMID:25146290. Hummingbird T1R1-T1R3 retains only low-affinity
  amino-acid responses PMID:25146290.
• The sugar-response-conferring substitutions are concentrated in the TAS1R3
  Venus-flytrap domain (109-residue region; 19 key substitutions)
  PMID:25146290, with additional contributing
  substitutions in TAS1R1.
• Receptor pharmacology (sugars/sugar-alcohols agonist; several human
  sweeteners inactive/aversive) matched taste behavior in both captive and
  wild hummingbirds (ruby-throated and Anna's hummingbirds respectively).
• Important caveat for this gene review: PMID:25146290 studied Calypte
  anna (Anna's hummingbird) and Archilochus colubris (ruby-throated
  hummingbird), not Oreotrochilus melanogaster (the species behind the
  UniProt accession reviewed here, a high-Andean hillstar). There is no
  UniProt entry, and apparently no published functional study, for T1R1/T1R3
  from O. melanogaster itself. All functional claims made in the ai-review
  YAML for this gene are by homology/lineage inference, not direct
  experimental evidence on this exact protein.

Deep research

genes/9AVES/TAS1R3/TAS1R3-deep-research-falcon.md (Falcon/Edison provider,
generated 2026-09-07) independently reaches the same conclusion: no
accession-, ORF-, or species-specific functional literature exists for
A0A7L3N407 / O. melanogaster Tas1r3; the InterPro domain architecture
(ANF_lig-bd_rcpt / GPCR_3 / GPCR_3_9-Cys_dom / GPCR_3_C) is consistent with a
class C TAS1R-family GPCR, and the recommended annotation is "probable
class-C, seven-transmembrane taste-receptor subunit... by hummingbird-lineage
homology... likely heterodimerizes with T1R1... to detect nectar
carbohydrates."

Annotation review summary

All 9 seeded GOA rows are IEA (ARBA/InterPro2GO/TreeGrafter/UniProt combined),
reviewed against PMID:25146290 and GO term definitions verified via QuickGO
(https://www.ebi.ac.uk/QuickGO/services/ontology/go/terms/...):

• GO:0033041 "sweet taste receptor activity" - ACCEPT. QuickGO definition
  ("Combining with soluble sweet compounds to initiate a change in cell
  activity") does not require the canonical TAS1R2 partner mechanism, so the
  hummingbird-repurposed TAS1R1-TAS1R3 dimer legitimately satisfies it. This
  is treated as the gene's core molecular function.
• GO:0050916 "sensory perception of sweet taste" and GO:0001582 (its BP
  detection-of-stimulus child) - ACCEPT, paralleling GO:0033041.
• GO:0050917 "sensory perception of umami taste" - KEEP_AS_NON_CORE. This
  is the ancestral, family-wide function of TAS1R1-TAS1R3 (still primary in
  most non-hummingbird birds), but PMID:25146290 shows it was largely
  superseded by the sweet-taste function in hummingbirds specifically, with
  only weak/low-affinity amino-acid responses retained. Not REMOVE (some
  retained low-affinity capacity, and no species-specific data to say it is
  fully lost in O. melanogaster), not co-equal ACCEPT (would overstate the
  minor residual capacity against the well-established, dominant sweet-taste
  function).
• GO:0004930 "G protein-coupled receptor activity", GO:0005886 "plasma
  membrane", GO:0007186 "GPCR signaling pathway" - ACCEPT as
  broad-but-accurate domain/family-based calls.
• GO:0050909 "sensory perception of taste" (broad ARBA parent) -
  KEEP_AS_NON_CORE: correct but redundant given the specific GO:0050916
  sweet-taste-perception annotation held below. GO:0016020 "membrane" -
  MARK_AS_OVER_ANNOTATED: correct but redundant given the more specific
  plasma-membrane annotation above. Both standardized to match the equivalent
  generic-term calls across all five taste-receptor genes in this PR (revised
  from an earlier ACCEPT for both, per the PR review below).

Revisions after PR review

The ai4c-reviewer bot's CHANGES_REQUESTED review on PR #3050 (2026-09-16)
flagged two issues, both fixed:

1. Generic-term policy (GO:0016020, GO:0050909, GO:0004930, GO:0007186) was
   applied inconsistently across the five taste-receptor genes in this PR.
   Standardized to: GO:0016020 → MARK_AS_OVER_ANNOTATED, GO:0050909 →
   KEEP_AS_NON_CORE (wherever a more specific sibling term is independently
   held), GO:0004930/GO:0007186 → ACCEPT.
2. core_functions[0].molecular_function used GO:0033041 directly, despite
   the same entry's own description stating "Neither subunit alone is
   functional." Changed to contributes_to_molecular_function, matching how
   the partner subunit TAS1R1 already modeled the identical situation.

Validation

Ran just validate 9AVES TAS1R3 after completing the review, and again after
the above revisions - both passed cleanly.

Related record

genes/9AVES/TAS1R1/ (UniProt A0A7L3NBT4, same species) is the obligate
dimerization partner for this receptor but its ai-review.yaml is still
INITIALIZED/PENDING as of this session - not reviewed here; a
separate review pass would be needed for TAS1R1. It also has the same wrong
placeholder taxon id (NCBITaxon:8782) in its seeded stub, which would need
the same correction to NCBITaxon:689266 if/when reviewed.