Odorant receptors proteins

The future in research will certainly lead to a better understanding of how odors are recognized, sorted, and classified. Studies promise, among other things, to determine whether perceptually similar, but stmcturaHy different, odors share the same class of receptor proteins, whether responses to odors can be modified, and possibly why olfactory neurons regenerate but other neurons do not. 

The G-proteins are heterotrimers made of three families of subunits, a, P, and y, which can interact specifically with discrete regions on G-protein-coupled receptors. This includes most receptors for neurotransmitters and polypeptide hormones (see Neuroregulators). G-protein-coupled receptors also embrace the odorant receptor family and the rhodopsin-linked visual cascade. 

By far the most studied family of the G-protein-coupled receptors are the rhodopsin-like receptors. These are also the largest group of receptors in number as they include receptors not only for the monoamines, nucleotides, neuropeptides and peptide hormones, but they also include the odorant receptors which number several hundreds of related receptors. These receptors have short N-termini, a conserved disulphide bridge between the TM2-TM3 and TM4—TM5 extracellular domains, and variable-length C-termini. In some cases the C-terminus is myristolyated which by tying the C-terminus to the cell membrane generates a fourth intracellular loop. 

Odorant receptor one of a class of proteins encoded by several hundred genes that are receptors for odorant molecules. 

Odorants are thought to bind to integral membrane receptors on the cilia of the olfactory sensory neurons. The receptors are thought to he specific different olfactory neuron types recognize different odorants that share certain characteristics (Buck, 1993). The odorant receptors transduce signals via interactions with G-proteins (so-called because guanosine trisphosphate is involved in their activation). These G-protein-coupled exhibit seven hydrophobic domains (Fig. 5.6). Variation in the amino acid sequence of the transmembrane domain may account for specificity and selectivity of odor reception. 

An important goal toward understanding sensation at the molecular level is the characterization of receptor proteins which bind a specific odorant or tastant Two approaches have been taken direct binding studies of stimulant with a receptor preparation, and identification of genes that code for receptor proteins. The weak reversible interactions make it difficult to stabilize such a complex for isolation and... 

The picture that has emerged from these studies is of an initial interaction of a stimulus with a matched portion of a receptor protein embedded in the cell membrane (13,65). This initial interaction causes stimulation of the linked G-protein to form cGMP. This is coupled to the reactivity of adenylate cyclase in the cells, leading to increased levels of cAMP, which opens ion channels in the cell membrane. A similar sequence can alternatively activate inositol phosphate as a second messenger. Either odorants, cAMP or cGMP can cause a potential change in the membrane (13,70,71,72). As in hormone-sensitive and neurotransmitter-... 

Members of the Gs subfamily are activated by hormone receptors, by odor receptors and by taste receptors. Gg-proteins mediate, e.g., signal transmission by adrenaline receptors of type P and by glucagon receptors. During perception of taste, the taste receptors are activated, which then pass the signal on via the olfactory G-protein Gou. Perception of sweet taste is also mediated via a Gs-protein. Transmission of the... 

There has been no research reported on the interaction of periplanones with pheromone-binding proteins or dendritic receptors. Nevertheless, two studies, one empirical and one theoretical, report on intrasensillar events in P. americana. Picim-bon and Leal (1999) determined the N-terminal amino acid sequences of two soluble proteins (putative odorant-binding proteins) that are specifically expressed in male antennae, and several other proteins that are expressed in antennae of both males... 

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