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
176 OR4A49P Human 11 4 A NG_004419 0 View
177 OR4A4P Human 299 11 4 A Q8NGN8 NG_004331 1 View
178 OR4A5 Human 315 11 4 A Q8NH83 NM_001005272 0 View
179 OR4A50P Human 11 4 A NG_004420 0 View
180 OR4A6P Human 11 4 A NG_004329 0 View
181 OR4A7P Human 11 4 A NG_004236 0 View
182 OR4A8 Human 315 11 4 A P0C604 NG_004235 0 View
183 OR4A9P Human 11 4 A NG_004333 0 View
184 OR4B1 Human 309 11 4 B Q8NGF8 NM_001194287 0 View
185 OR4B2 Human 11 4 B 0 View
186 OR4C10P Human 11 4 C NG_002264 0 View
187 OR4C11 Human 310 11 4 C Q6IEV9 NM_001004700 0 View
188 OR4C12 Human 309 11 4 C Q96R67 NM_001005270 0 View
189 OR4C13 Human 309 11 4 C Q8NGP0 NM_001001955 0 View
190 OR4C14P Human 11 4 C NG_004234 0 View
191 OR4C15 Human 316 11 4 C Q8NGM1 NM_001001920 0 View
192 OR4C16 Human 310 11 4 C Q8NGL9 NM_001004701 0 View
193 OR4C1P Human 11 4 C NG_002184 0 View
194 OR4C2P Human 11 4 C NG_002250 0 View
195 OR4C3 Human 302 11 4 C Q8NH37 NM_001004702 0 View
196 OR4C45 Human 311 4 C A6NMZ5 KP290451 0 View
197 OR4C46 Human 309 11 4 C A6NHA9 NM_001004703 0 View
198 OR4C48P Human 4 C NG_004421 0 View
199 OR4C49P Human 4 C NG_004422 0 View
200 OR4C4P Human 11 4 C NG_002275 0 View
Showing 176 to 200 of total 2067 entries