Olfactory Receptors (ORs) are the physical barriers between the environment and the brain. ORs are members of the GPCR-rhodopsin family, which is involved in cell recognition, signal transduction activation, and sense mediation. OR is made up of seven transmembrane (TM) helical domains bound by three putative extracellular loops (EL) and three putative intracellular loops (IL), an extracellular N-terminus, and an intracellular C-terminus. At the intersection of TM3 and IL2, the intracellular loop includes a conserved sequence motif, the aspartate-arginine-tyrosine (DRY) amino acid motif, which is a hallmark of GPCRs. The TM1, TM2, and TM7 are all conserved. The binding site specificity is determined by the amino acid side chains of the central TM domains, which are structurally diverse. The binding pocket of ORs has a hydrophobic environment, indicative of hydrophobic interactions between odorants and ORs. The binding specificity of ORs is influenced not only by the central TM-domains hyper-variable region, but also by the N-termini and C-termini. Both terminals are small, with only about 20 amino acids each. The conserved cysteine residues in the EL1 and EL2-loops are involved in inter- and intramolecular disulphide linkages. One of the three cysteine restudies in EL2-loop has a specific role. A metal binding site is formed by the sequence motif (HXXC[DE]) in EL2-loop. On binding with Zn(II) or Cu, the EL2-loop transforms into a -helical structure confirmation (eighth helix) (II).When an odorant with a high affinity for metal ions replaces one of the metal-ligated amino acids in the EL2-loop, ORs undergo structural rearrangement, which is necessary for the activation of G-olf proteins attached to OR receptors. On the cytoplasmic side of the TM domains, the sequence motifs KAFSTC, PMYFFL, and YRDYAM play a role in OR folding and activation. The amino acid residues on the extracellular side of TM domains are variable, indicating a wide range of possible odorant recognition sites.

OlfactionBase lists 2067 ORs from two species (Human (851) and Mus musculus (1216)).

Sr. No Receptor Organism Length Chromosome Family Sub Family UniProt GenBank #Odorants Details
151 OR3B1P Human 3 B NG_004382 0 View
152 OR3D1P Human 1 3 D NG_004862 0 View
153 OR4A10P Human 11 4 A NG_004334 0 View
154 OR4A11P Human 11 4 A NG_004332 0 View
155 OR4A12P Human 11 4 A NG_004243 0 View
156 OR4A13P Human 11 4 A NG_004242 0 View
157 OR4A14P Human 11 4 A NG_004241 0 View
158 OR4A15 Human 344 11 4 A Q8NGL6 NM_001005275 0 View
159 OR4A16 Human 328 11 4 A Q8NH70 NM_001005274 0 View
160 OR4A17P Human 11 4 A NG_004335 0 View
161 OR4A18P Human 11 4 A NG_004240 0 View
162 OR4A19P Human 11 4 A NG_004239 0 View
163 OR4A1P Human 11 4 A NG_002173 0 View
164 OR4A21P Human 11 4 A NG_004238 0 View
165 OR4A2P Human 11 4 A NG_004330 0 View
166 OR4A3P Human 11 4 A NG_004237 0 View
167 OR4A40P Human 11 4 A NG_004327 0 View
168 OR4A41P Human 11 4 A NG_004413 0 View
169 OR4A42P Human 11 4 A NG_004414 0 View
170 OR4A43P Human 11 4 A NG_004328 0 View
171 OR4A44P Human 11 4 A NG_004415 0 View
172 OR4A45P Human 11 4 A NG_004416 0 View
173 OR4A46P Human 11 4 A NG_004417 0 View
174 OR4A47 Human 309 11 4 A Q6IF82 NM_001005512 0 View
175 OR4A48P Human 11 4 A NG_004418 0 View
Showing 151 to 175 of total 2067 entries