TAS1R1

Summary: This fragment carries the canonical class C GPCR domain architecture (VFT/ANF ligand-binding region, 9-Cys linker, and a 7TM "GPCR family 3" domain with three predicted transmembrane helices), consistent with TAS1R1's established identity as a family C GPCR subunit.

Reason: The InterPro domain matches recorded on this record (ANF_lig-bd_rcpt, GPCR_3, GPCR_3_9-Cys_dom/sf, GPCR_3_C) and the UniProt-annotated 7TM "G-protein coupled receptors family 3 profile" domain (residues 438-533) with three transmembrane helices are diagnostic of a class C GPCR, and TAS1R1 orthologs are established GPCRs across vertebrates: "In vertebrates, sweet and savory... tastes are sensed by G protein-coupled receptors (GPCRs) termed T1Rs." GPCR-activity is family-architecture evidence, independent of whether this particular lineage's receptor detects sugars or amino acids, so the call is sound even though this exact accession/species has not been assayed directly.

Summary: Class C GPCRs, including all characterized TAS1R subunits, are cell-surface receptors; this fragment retains three predicted transmembrane helices consistent with a multi-pass plasma-membrane protein.

Reason: UniProt's own subcellular-location call for this record ("Cell membrane... Multi-pass membrane protein") plus the three TRANSMEM features (440-464, 476-497, 509-532) support plasma-membrane localization. Heterologously expressed hummingbird T1R1-T1R3 traffics to and signals from the cell surface in the founding functional study (HEK293T calcium-reporter assays), consistent with native plasma-membrane residence. This is expected identity-level evidence; it is not itself evidence of the fragment's ligand specificity.

Summary: Consistent with TAS1R1's class C GPCR domain architecture and with TAS1R1-TAS1R3's established role initiating G-protein-mediated taste signal transduction.

Reason: Direct consequence of the GPCR molecular function; T1R1-T1R3 signaling in taste cells canonically proceeds through a G-protein/PLCbeta2/IP3/ Ca2+/TRPM5 cascade regardless of whether the ligand is an amino acid (ancestral/umami) or a carbohydrate (derived, hummingbird-specific). The process-level GPCR signaling call does not depend on resolving that ligand-specificity question.

Summary: Generic membrane call from the same InterPro domain matches that support the more specific plasma-membrane annotation.

Reason: Correct but less informative than the co-annotated GO:0005886 (plasma membrane), which is separately supported and preferred as the core location; the generic term is redundant given that more specific, independently-supported annotation. Not core. Consistent with the equivalent generic-membrane calls for the TAS2R38/TAS2R16/TAS1R3 genes in this same PR.

Summary: Broad, accurate parent process term: TAS1R1 is a taste receptor subunit regardless of whether its ligand-specificity is ancestral (umami) or hummingbird-derived (sweet/carbohydrate).

Reason: Uncontroversial at this level of generality; both the ancestral umami-sensing role of TAS1R1-TAS1R3 and the hummingbird-specific sweet-sensing repurposing are instances of "sensory perception of taste." Retained as a valid but non-core parent term, since the more specific process calls below already cover this gene's role. Consistent with the equivalent calls for the other taste-receptor genes in this same PR.

Summary: TreeGrafter/PANTHER-propagated umami-taste call reflects the ancestral, tree-wide TAS1R1 function (retained in chicken, swift, and most other vertebrates), but is very likely stale for the hummingbird (Trochilidae) lineage this record belongs to, where TAS1R1-TAS1R3 has been experimentally shown (in a congeneric/confamilial species, Calypte anna) to have been repurposed to detect carbohydrates rather than amino acids.

Reason: GO:0050917 is defined as perception of "the savory taste of meats and other foods that are rich in glutamates" - i.e. amino-acid/glutamate detection. That is the correct, ancestral TAS1R1-TAS1R3 function, and it is retained in non-hummingbird birds: "cells expressing chicken or swift T1R1-T1R3 failed to detect carbohydrates at any concentration tested and instead recognized alanine and serine." But hummingbirds transformed this same receptor complex after diverging from swifts: "Receptor expression studies revealed that the ancestral umami receptor (the T1R1-T1R3 heterodimer) was repurposed in hummingbirds to function as a carbohydrate receptor," and behavioral assays in multiple hummingbird species confirmed this receptor logic drives sugar-seeking taste behavior. Oreotrochilus melanogaster is a hummingbird (family Trochilidae), so by strong phylogenetic/functional inference its TAS1R1-TAS1R3 more likely mediates carbohydrate (sweet) perception than umami perception, even though this exact species and accession have not been assayed. Some residual amino-acid sensitivity may persist ("low-affinity responses were observed to some amino acids"), so umami sensing is not necessarily fully abolished. TAS1R1 and TAS1R3 are an obligate heterodimer with a single shared ligand spectrum (see PMID:25146290: "Responses were not observed when T1R1 or T1R3 alone was used"), so this call is kept identical to the equivalent GO:0050917 row on the partner subunit TAS1R3 (genes/9AVES/TAS1R3): retained as a non-core, likely-partially-retained ancestral function, while sweet-taste detection (GO:0050916/GO:0033041, see below and in TAS1R3) is treated as the core, derived function of this receptor complex in the hummingbird lineage. KEEP_AS_NON_CORE rather than REMOVE or MODIFY because the underlying capacity is plausibly retained at low affinity, not clearly absent or simply mis-termed.

Summary: NEW: proposed addition reflecting the hummingbird-specific TAS1R1-TAS1R3 sweet-taste repurposing (see review of GO:0050917 above); mirrors the annotation already present on the partner subunit TAS1R3 in this genome.

Reason: Not present in GOA for this record (TreeGrafter placed TAS1R3, but not TAS1R1, in the sweet-taste-annotated PANTHER node), but strongly supported by the same evidence base as the GO:0050917 KEEP_AS_NON_CORE review above: hummingbird T1R1-T1R3 is an obligate heterodimer whose sugar responses require both subunits, and behavioral data confirm this drives sugar-taste preference in hummingbirds. Encoded as ISS (inferred from sequence/structural similarity), with no GO_REF, since this is a curator-proposed cross-species inference (from Calypte anna data) rather than a genuine TreeGrafter/GOA-sourced row for this record. Proposed with moderate rather than high confidence because it rests on that cross-species/cross-genus inference rather than a direct assay of Oreotrochilus melanogaster or this fragment.