Guanylyl Cyclases as a Family of Putative Odorant Receptors

Abstract

Mammals can discriminate among a large number (> 10,000) of unique odorants. The most highly supported explanation for this ability is that olfactory neurons express a large number of seven transmembrane receptors that are not spatially organized at the level of the olfactory epithelium, but whose axonal projections form a distinct pattern within the olfactory bulb. The odor-induced signaling pathway in olfactory neurons includes a Gs-like protein (G(olf)) that activates a specific adenylyl cyclase (type III) isoform, resulting in elevations of cyclic AMP and subsequent activation of a cyclic nucleotide-gated channel. The channel also can be regulated by cyclic GMP. Recently, an olfactory neuron-specific guanylyl cyclase was discovered in rodents, and subsequently a large family of sensory neuronal guanylyl cyclases was identified in nematodes. These guanylyl cyclases are concentrated in the plasma membrane of the dendritic cilia and contain extracellular domains that retain many of the primary sequence characteristics of guanylyl cyclases known to be receptors for various peptides. Thus, the guanylyl cyclases appear to represent a second family of odorant/pheromone receptors.

Nitric oxide regulates K + and Cl - channels in guard cells through a subset of abscisic acid-evoked signaling pathways

“…A second mode of cGMP action entails binding and direct activation of cyclic nucleotide-gated ion channels (CNGCs). In animals, CNGCs are found at the plasma membrane and are active in visual, taste, and olfactory signal transduction (1,29,30). Less is known of plant CNGCs, but they seem to have roles in pathogen defense responses (31,32).…”

“…It is a byproduct of several cellular reactions and a natural constituent of all living cells, but its functions are known principally from studies of mammalian physiology (1)(2)(3). In animals, NO acts indirectly through guanylate cyclase to activate cGMP-dependent cellular responses and directly through S-nitrosylation of elements downstream of several signal cascades (3).…”

Sniffing out social signals

“…What, if any, chemosensory role is fulfilled by these cells? Ever since their discovery, the common structure of receptor GC proteins [16] -an extracellular peptide binding domain coupled to an intracellular catalytic domain by a single transmembrane α-helix -has fueled speculation about GC-D-positive OSNs as peptide sensors that regulate intracellular cGMP levels. At present, a conclusive picture of how these cells are functionally involved in olfaction is lacking.…”

Introduction to Olfaction: Perception, Anatomy, Physiology, and Molecular Biology

“…An alternate signaling pathway for olfactory transduction has recently been proposed by Gibson and Garbers [58]. They have found a large family of olfactory neuron-specific guanylyl cyclases that are membrane-bound and contain extracellular domains that may constitute a second family of odorant receptors.…”