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
51 OR2A9P Human 7 2 A NR_002157 0 View
52 OR2AD1P Human 6 2 AD NG_002239 0 View
53 OR2AE1 Human 323 7 2 AE Q8NHA4 KP290172 0 View
54 OR2AF1P Human 2 AF NG_002257 0 View
55 OR2AG1 Human 316 11 2 AG Q9H205 NM_001004489 1 View
56 OR2AG2 Human 316 11 2 AG A6NM03 KP290536 0 View
57 OR2AH1P Human 11 2 AH NG_004244 0 View
58 OR2AJ1 Human 328 1 2 AJ Q8NGZ0 KP290475 0 View
59 OR2AK2 Human 335 1 2 AK Q8NG84 KP290444 0 View
60 OR2AL1P Human 11 2 AL NG_002273 0 View
61 OR2AM1P Human 9 2 AM NG_004255 0 View
62 OR2AO1P Human 7 2 AO NG_004409 0 View
63 OR2AP1 Human 309 12 2 AP Q8NGE2 KP290320 0 View
64 OR2AQ1P Human 1 2 AQ NG_004276 0 View
65 OR2AS1P Human 1 2 AS NG_004705 0 View
66 OR2AS2P Human 1 2 AS NG_004706 0 View
67 OR2AT4 Human 320 11 2 AT A6NND4 KP290546 1 View
68 OR2B11 Human 317 1 2 B Q5JQS5 KP290627 4 View
69 OR2B2 Human 357 6 2 B Q9GZK3 KP290568 0 View
70 OR2B3 Human 313 6 2 B O76000 KP290156 3 View
71 OR2B4P Human 6 2 B NG_004686 0 View
72 OR2B6 Human 313 6 2 B P58173 NM_012367 0 View
73 OR2B7P Human 6 2 B NG_004280 0 View
74 OR2B8P Human 312 6 2 B P59922 NG_003194 0 View
75 OR2BH1P Human 11 2 BH NG_004410 0 View
Showing 51 to 75 of total 2067 entries