http://www.columbia.edu/~col8/BuckAxel_ORcloning_Cell91.pdf

A novel multigene family may encode odorant receptors: A molecular basis for odor recognition

Odorant-selective genes and neurons mediate olfaction in C. elegans

Olfactory transduction is thought to be initiated by the binding of odorants to specific receptor proteins in the cilia of olfactory receptor cells (reviewed in refs 1–3). The mechanism by which odorant binding could initiate membrane depolarization is unknown, but the recent discovery of an odorant-stimulated adenylate cyclase in purified olfactory cilia4,5 suggests that cyclic AMP may serve as an intracellular messenger for olfactory transduction. If so, then there might be a conductance in the ciliary plasma membrane which is controlled by cAMP. Here we report that excised patches of ciliary plasma membrane, obtained from dissociated receptor cells, contain a conductance which is gated directly by cAMP. This conductance resembles the cyclic GMP-gated conductance that mediates phototransduction in rod and cone outer segments6,7, but differs in that it is activated by both cAMP and cGMP. Our data provide a mechanistic basis by which an odorant-stimulated increase in cyclic nucleotide concentration could lead to an increase in membrane conductance and therefore, to membrane depolarization. These data suggest a remarkable similarity between the mechanisms of olfactory and visual transduction and indicate considerable conservation of sensory transduction mechanisms.

A cyclic nucleotide-gated conductance in olfactory receptor cilia

Receptor-effector coupling by G proteins

▪ Abstract Olfaction begins with the transduction of the information carried by odor molecules into electrical signals in sensory neurons. The activation of different subsets of sensory neurons to different degrees is the basis for neural encoding and further processing of the odor information by higher centers in the olfactory pathway. Recent evidence has converged on a set of transduction mechanisms, involving G-protein-coupled second-messenger systems, and neural processing mechanisms, involving modules called glomeruli, that appear to be adapted for the requirements of different species. The evidence is highlighted in this review by focusing on studies in selected vertebrates and in insects and crustaceans among invertebrates. The findings support the hypothesis that olfactory transduction and neural processing in the peripheral olfactory pathway involve basic mechanisms that are universal across most species in most phyla.

Mechanisms of olfactory discrimination : Converging evidence for common principles across phyla

The mechanism of the sense of smell has long been a subject for theory and speculation. More recently, the notion of odorant recognition by stereospecific protein receptors has gained wide acceptance, but the receptor molecules remained elusive. The recognition molecules are believed to be quite diverse, which would partly explain the unusual difficulties encountered in their isolation by conventional ligand-binding techniques. An alternative approach would be to probe the receptors through transductory components that may be common to all receptor types. Here we report the identification of one such transductory molecular component. This is an odorant-sensitive adenylate cyclase, present in very large concentrations in isolated dendritic membranes of olfactory sensory neurones. Odorant activation of the enzyme is ligand and tissue specific, and occurs only in the presence of GTP, suggesting the involvement of receptor(s) coupled to a guanine nucleotide binding protein (G-protein). The olfactory G-protein is independently identified by labelling with bacterial toxins, and found to be similar to stimulatory G-proteins in other systems. Our results suggest a role for cyclic nucleotides in olfactory transduction, and point to a molecular analogy between olfaction and visual, hormone and neurotransmitter reception. Most importantly, the present findings reveal new ways to identify and isolate olfactory receptor proteins.

Odorant-sensitive adenylate cyclase may mediate olfactory reception

https://www.cell.com/trends/biochemical-sciences/pdf/0968-0004(89)90106-0.pdf

Invasive adenylate cyclase toxin of Bordetella pertussis

Bordetella pertussis produces a calmodulin-sensitive adenylate cyclase (AC) which is an essential virulence factor in mammalian pertussis. Here we report the purification and characterization of the toxic form of the enzyme, which penetrates eukaryotic cells and generates high levels of intracellular cAMP. This form was purified from an extract of B.pertussis strain carrying a recombinant plasmid which over-produced both enzymatic and toxic activities of the enzyme. Western blot analysis of the extract using anti-B.pertussis AC antibodies detected only one protein of 200 kd. However, gel filtration of the extract resolved two peaks of enzymatic activity. The first peak of aggregated material contained greater than 70% of the total enzymatic activity, and the second peak contained the majority of the toxic activity. Purification of the enzyme from both peaks yielded proteins of 200 kd, with similar biochemical and immunological properties. Yet only the enzyme purified from the second peak could penetrate human lymphocyte and catalyse the formation of intracellular cAMP. B.pertussis AC gene expressed in Escherichia coli produced a calmodulin-dependent enzyme of 200 kd, which lacked lymphocyte penetration capacity. It is proposed that a post-translational modification that occurs in B.pertussis but not in E.coli confers upon the 200 kd protein of B.pertussis AC the toxic properties.

Bordetella pertussis adenylate cyclase: purification and characterization of the toxic form of the enzyme.

Cloning of the adenylate cyclase genetic determinant of Bordetella pertussis and its expression in Escherichia coli and B. pertussis.

https://febs.onlinelibrary.wiley.com/doi/pdf/10.1016/0014-5793%2883%2980805-9

Emanuel Hanski

Papers

Odorant-sensitive adenylate cyclase may mediate olfactory reception

Invasive adenylate cyclase toxin of Bordetella pertussis

Bordetella pertussis adenylate cyclase: purification and characterization of the toxic form of the enzyme.

Cloning of the adenylate cyclase genetic determinant of Bordetella pertussis and its expression in Escherichia coli and B. pertussis.

Activation of adenylate cyclase by sperm membranes. The role of guanine nucleotide binding proteins.