Olfactory receptor proteins

Pevsner, J., Trifiletti, R., Strittmatter, S. M., and Synder, S. H. (1985). Isolation and characterization of an olfactory receptor protein for odorant pyrazines. Proc. Natl. Acad. Sci. USA 82, 3050-3054. 

Danty E., Comuet J. M. and Masson C. (1994) Honeybees have putative olfactory receptor proteins similar to those of vertebrates. C. R. Acad. Sci. Ill 317, 1073-1079. 

There is a general consensus that the interaction of odor molecules with suitable olfactory receptor proteins in the chemosensory membrane is the initial step for... 

Vertebrates possess three primary chemosensory systems gustation ( taste ), trigeminal, and olfaction ( smell ) but only one of these, the olfactory system, mediates responses to pheromones. Chemicals that stimulate the olfactory system are known as odorants and comprise one type of biological cue (any entity that stimulates a sensory system). Bouquets of odorants that can be discriminated as specific entities are termed odors. The olfactory system contains olfactory receptor neurons (ORNs) that comprise cranial nerve I and project directly to the forebrain. ORNs are now known to express only one to a few olfactory receptor proteins ( receptors ), which means that the chemoreceptive range of each neuron can be very narrow. The olfactory system also has several subcomponents including the vomeronasal organ, which is described below. 

The structure/activity relationship (SAR) tools employed in odor research are essentially the same standard tools used in all applications, and the models developed fall into the categories of substrate and receptor models. The pharmaceutical industry is the leader in SAR techniques, and the fragrance industry tends to follow its lead. Early models were substrate based, but the discovery of the genes that code for the olfactory receptor proteins has also allowed receptor models to be constructed. 

Pilpel Y, Lancet D. The variable and conserved interfaces of modeled olfactory receptor proteins. Protein Sci. 1999 8 969-977. Man O, Gilad Y, Lancet D. Prediction of the odorant binding site of olfactory receptor proteins by human-mouse comparisons. Protein Sci. 2004 13 240-254. 

Pilpel Y, Lancet D. The variable and conserved interfaces of modelled olfactory receptor proteins. Protein Sci. 2002 8 969-977. 

Strotmann J, Wanner I, Krieger J, Raming K, Breer H (1992) Expression of odorant receptors in spatially restricted subsets of chemosensory neurones. Neuroreport 3(12) 1053—1056 Strotmann J, Conzelmann S, Beck A, Feinstein P, Breer H, Mombaerts P (2000) Local permutations in the glomerular array of the mouse olfactory bulb. J Neurosci 20(18) 6927-6938 Strotmann J, Levai O, Fleischer J, Schwarzenbacher K, Breer H (2004) Olfactory receptor proteins in axonal processes of chemosensory neurons. J Neurosci 24(35) 7754-7761 Taniguchi M, Nagao H, Takahashi YK, Yamaguchi M, Mitsui S, Yagi T, Mori K, Shimizu T (2003) Distorted odor maps in the olfactory bulb of semaphorin 3A-deficient mice. J Neurosci 23(4) 1390-1397... 

Receptors can be isolated and immobilized on the transducer surface, but for the purpose a complete organelle can be employed, e.g., animal or insect antennule, or nerve fibers,132 where different sensitivity was demonstrated for various stimuli (amino acids and closely-related analogs). For comparison, the biosensor made with isolated olfactory receptor proteins, immobilized on the surface of piezoelectric crystal, exhibited sensitivity to different volatile compounds.134... 

Most mammals use about 700-800 different types of olfactory receptor proteins in their noses. Humans, chimpanzees, gorillas, orangutans and rhesus macaques use only about half that number. Interestingly, these species are the only animals to possess colour vision and so it would seem that there has been an evolutionary trade-off between smell and colour vision. The rate of loss of olfactory receptor genes is higher in humans than in the other primates, indicating our increased dependence on vision rather than smell (Gilad et al., 2003). 

Odor molecules interact with olfactory receptor proteins on the surface of each ORN. In arthropods there are hundreds of different olfactory receptor proteins depending on species, each with a broad sensitivity/range of molecules which will interact with (Hallem and Carlson 2006). Each receptor s sensitivities overlap with those of other receptor proteins, so that a huge olfactory world can be covered. Each ORN presents just one of the different olfactory receptor proteins. Chemosensory systems are discussed in chapters by Hallberg and Skog (Chap. 9), and Schmidt and Mellon (Chap. 7). Derby and Sorensen (2008) remind us that detectors of pheromones and olfactory social cues are not exclusively located in the aesthetasc/olfactory pathway, giving as an example male crayfish which have sensors on their claws that detect female odors. 

The process of smelling begins when scents in the inhaled air approach the olfactory epithelium (Regio olfactoria) (Fig. 3.1 and 3.2). Richard Axel and Linda B. Buck (Nobel Prize laureates for Pharmacy or Medicine in 2004) identified 339 intact, trans-membrane olfactory receptor proteins, to which transport protein-associated scent molecules can bind. 

The diversity of human olfactory acuity, as defined by specific anosmia, may be caused by the diversity of the olfactory receptor protein repertoire in humans. Physiologically, humans have a limited number of clearly defined olfactory receptor types that modulate odor perception in response to a small recurrent set of odorants distributed throughout the natural world. For example, the Flavornet lists about 500 chemicals reported to be above their threshold in natural products [39,40]. Natural products contain a subset of functional odorants, above their threshold, that invoke perceptions that humans experience as odor. The same odorants are found in many natural products but in different relative concentrations. Tested individually, these odorants produce precepts that have been... 

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