OR3A4P

Model summary

A human seven-pass cell-surface receptor that detects volatile odorants and converts their binding into intracellular signals through heterotrimeric G proteins. By residing in the plasma membrane and using a rhodopsin-like transmembrane core, it initiates the olfactory signaling cascade that elevates cyclic nucleotide levels and drives neuronal responses underlying the sense of smell. Its multi-pass architecture positions an extracellular ligand-binding cavity and intracellular coupling loops to control pathway activation and signal amplitude.

Predicted Gene Ontology terms

1. 01

   I begin with the InterPro architecture.

   The core transmembrane engine is IPR017452 (GPCR, rhodopsin-like, 7TM domain, residues 44–293), which encodes the canonical seven-helix bundle that transduces extracellular ligand binding into intracellular G-protein activation. This structural core is embedded within multiple rhodopsin-like GPCR family signatures: IPR000276 (G protein-coupled receptor, rhodopsin-like family) appears in several positions—[29–53], [62–83], [107–129], and [202–225]—marking conserved motifs that stabilize the inactive and active states and couple to heterotrimeric G proteins. Superimposed on this GPCR scaffold is IPR000725 (Olfactory receptor family, residues 35–297), which specifies the receptor subclass that recognizes volatile odorants. The ordered layout—an N-terminal extracellular region feeding into a 7TM bundle and intracellular loops—causes ligand-triggered conformational switching that recruits and activates G proteins.

2. 02

   This architecture dictates the molecular function.

   The olfactory receptor family signature (IPR000725) constrains ligand chemistry to small hydrophobic odorants and the rhodopsin-like 7TM core (IPR017452) provides the allosteric machinery for signal transduction. Together, these features define GO:0004984 olfactory receptor activity: binding odorants and initiating downstream signaling via G proteins.

3. 03

   From this function, the biological process follows.

   Odorant-evoked GPCR signaling is the initiating step of chemosensory perception in the olfactory epithelium; thus the receptor’s activity directly drives GO:0007608 sensory perception of smell. The causal chain is: odorant binding in the extracellular cavity triggers helix rearrangements in the 7TM bundle, which activate Golf-class G proteins and elevate cAMP, ultimately encoding odor information.

4. 04

   Cellular location is implied by both topology and sequence features.

   The seven-pass bundle and absence of soluble domains place the protein in the lipid bilayer as a multi-pass membrane receptor. This supports a membrane-resident assignment and specifically aligns with GO:0005886 plasma membrane, consistent with the stated cell membrane localization and multi-pass topology.

5. 05

   Mechanistically, the receptor likely binds odorants within a transmembrane pocket formed by helices III, V, and VI, with conserved rhodopsin-like motifs stabilizing active and inactive conformations.

   The intracellular loops and C-terminal tail recruit heterotrimeric G proteins—most plausibly the olfactory G alpha subunit—to stimulate adenylyl cyclase, raising cAMP and opening cyclic nucleotide-gated channels. I therefore hypothesize transient complexes with Golf (GNAL) and Gβγ subunits, followed by coupling to adenylyl cyclase III and downstream ion channels. Accessory factors that chaperone and traffic olfactory receptors are also plausible partners, ensuring correct membrane delivery and signal fidelity.