Olfactory sensory neurons expressing different members of the mOR37 odourant receptor subfamily s... more Olfactory sensory neurons expressing different members of the mOR37 odourant receptor subfamily send their axons to distinct glomeruli located in the immediate vicinity in the olfactory bulb [Strotmann, J., Conzelmann, S., Beck, A., Feinstein, P., Breer, H. & Mombaerts, P. J. Neurosci., 20, 6927±6938]. In this study, the potential of transgenic mouse lines was used to explore the onset of receptor expression, the outgrowth of axons as well as the glomerulus formation for two neuron populations expressing different mOR37 subtypes. The data indicate a synchronous time course of these features for both neuron populations. From E15 until the day of birth, the axons of the two mOR37 populations terminate in a common, small area of the presumptive olfactory bulb. During a short postnatal phase, the two axon populations segregate into distinct, protoglomerular structures; some aberrant ®bers can still be observed during this period.
Voltage-dependent Ca2+ channels are considered as molecular trigger elements for signal transmiss... more Voltage-dependent Ca2+ channels are considered as molecular trigger elements for signal transmission at chemical synapses. Due to their central role in this fundamental process, function and pharmacology of presynaptic Ca2+ channels have recently been the subject of extensive exploration employing various experimental techniques. Several lines of evidence indicate that, at nerve terminals in higher vertebrates, the evoked influx of Ca2+ -ions is mainly mediated by Ca2+ channels of the P-type. The stringent regulation of presynaptic Ca2+ channels is supposed to be involved in fine-tuning the efficiency of synaptic transmission. Intrinsic control mechanisms, such as voltage- or Ca(2+)-dependent inactivation, or modulation of channel activity, either by G-proteins directly or via phosphorylation by protein kinases, may be of particular functional importance.
The rapid and transient generation of pulses of either cAMP or IP3 is considered the primary reac... more The rapid and transient generation of pulses of either cAMP or IP3 is considered the primary reaction in olfactory signal transduction. There is some recent evidence suggesting that another second messenger system, involving cGMP, may also play an important role in olfactory signalling. High doses of odorant elicit a delayed and sustained elevation of cGMP /evels due to the operation of the nitric oxide (NO) synthase/guanylyl cydase system. The interplay of NO and cGMP is supposed to trigger molecular mechanisms, induding adaptation processes, which enable the olfactory neuroepithe/ium to cope with strong stimuli. Furthermore, a characteristic pattern of staining for NO synthase in the olfactory bulb suggests that the NO/cGMP system may also participate in neuronal processing of the sensory input.
Abstraet--A combination of the stopped-flow technology with dual channel spectrofluorometry of Ca... more Abstraet--A combination of the stopped-flow technology with dual channel spectrofluorometry of Ca 2+indicators was utilized for the measurement of rapid Ca2+-signals in rat cerebral cortical synaptosomes evoked by K+-depolarization. There was no observable contribution of Ca 2 +_ions from intracellular stores to the rise in [Ca2+],. The kinetics of the fast increase in intracellular Ca 2+ concentration was analysed in relation to the depolarization strength. The maximal increase in [Ca2+], and the time course of Ca 2÷channel inactivation were determined for depolarizations obtained by different extracellular K+-concentrations ([K+]o). An apparent threshold was observed at about 18 mM [K+]o; a maximal Ca2+-signal amplitude was estimated at about 40 mM [K +]o. Pharmacological properties of the involved Ca 2+-channels were determined using selective Ca2+-channel blockers (Dihydropyridines, to-Conotoxin, o~-Agatoxins);
Sall3 is a member of a gene family with homology to the spalt gene of Drosophila melanogaster, en... more Sall3 is a member of a gene family with homology to the spalt gene of Drosophila melanogaster, encoding transcription factors, and acts as downstream target of hedgehog. Vertebrate homologues of spalt have been shown to be involved in development of the limbs and nervous system and several organs including the kidney and heart; mutations in the genes are implicated in several human genetic disorders. Recent studies have shown a total loss of olfactory bulb (OB) dopaminergic (DA) neurons in Sall3-null mice. We assume that tyrosine hydroxylase (TH) may be regulated by Sall3 in OB. In this study, we find that Sall3 and TH co-localize in glomerular layer (GL) of OB. Furthermore, we demonstrate a significant induction of the proximal TH promoter transcription activity by Sall3 in dual-luciferase reporter assay and a reduction of TH expression level in Sall3-deficient cell lines. Collectively, these findings support the notion that Sall3 correlates with the expression of TH in mouse OB and may have a role in OB DA neuron development by regulating TH gene expression. The results from this study may advance our understanding of the molecular pathways of OB in the DA neuron development and differentiation.
The responsiveness of isolated olfactory sensory neurons to stimulation with aliphatic aldehydes ... more The responsiveness of isolated olfactory sensory neurons to stimulation with aliphatic aldehydes of varying chain length (5-10 hydrogenated carbon atoms) was investigated by means of Ca(2+ )imaging. More than half the cells examined were responsive to aliphatic aldehydes. Individual cells did not react or reacted to one or multiple aldehydes; in the latter case, cells only reacted to aldehydes of consecutive carbon chain lengths. The largest proportion of cells responded to octanal. It was also demonstrated that a structural difference as small as one hydrogenated carbon atom was detectable by the olfactory neurons. Neurons were increasingly able to discriminate between two aldehydes as the difference in chain length between the two increased. Discrimination between aldehydes with longer carbon chains was reduced. Although the odorants examined belong to a distinct chemical class and differ only slightly in structure, individual olfactory sensory neurons showed quite different recep...
The detection of volatile odorants is supposed to begin with their interaction with soluble bindi... more The detection of volatile odorants is supposed to begin with their interaction with soluble binding proteins which shuttle the hydrophobic ligands through the aqueous mucus layer towards specific odorant receptors in the ciliary membrane of olfactory neurons. A large family of receptors for odorants has been identified recently; individual receptor types are expressed in subsets of cells distributed in distinct zones of the olfactory epithelium. Ligand-receptor interaction triggers a rapid multistep reaction cascade, ultimately leading to an electrical response of the receptor neuron. Olfactory signaling is terminated by phosphorylation of receptors via a negative feedback reaction catalyzed by two types of kinases.
Density measurements made on cholinergic synaptic vesicles from the electric organs of Torpedo ma... more Density measurements made on cholinergic synaptic vesicles from the electric organs of Torpedo marmorata at different osmotic pressures are consistent with the following structural model of the vesicle. The particle behaves like a sphere 80-100 nm in diameter bounded by a semi-permeable membrane. The bulk of its soluble constituents are in true solution at physiological osmolalities. The limiting membrane is approximately 4-5 nm thick, suggesting that it contains large areas of phospholipid bilayer exposed to its bathing medium. The limiting membrane takes up about 26% (v/v) of the particle, a further 34% (v/v) of which is osmotically active water and 31% (v/v) hydrated core material at 800 mosmol/1. The buoyant density of the membrane is 1.132 g . cm-3. The density of the hydrated core material is approximately 1.05 g . cm-3. The membrane is selectively permeable to small molecules when subjected to hypo-osmotic stress. It is proposed that this occurs by the formation of small transient pores in the lipid bilayer of the membrane, which are induced by stretching caused by the osmotic pressure change.
The reception of odorous molecules occurs in chemosensory neurons which encode the strength, dura... more The reception of odorous molecules occurs in chemosensory neurons which encode the strength, duration and quality of odorant stimuli into distinct patterns of afferent neuronal signals which travel along the cells' axons towards the brain where decoding of the olfactory message is initiated. Our understanding of the molecular mechanisms mediating the primary events of odor detection has lagged behind the knowledge about other sensory modalities.
The complex physiology of the gastrointestinal (GI) tract must permanently be adjusted according ... more The complex physiology of the gastrointestinal (GI) tract must permanently be adjusted according to the composition of ingested food, which requires continuous monitoring by appropriate sensory systems. Sensing the dietary constituents is thought to be mediated by chemosensory cells residing in the mucosa of the GI tract. We have examined the appearance and differentiation of candidate chemosensory cells at distinct postnatal stages and visualized cells that express gustducin or TRPM5. Two critical stages have been considered: the suckling period when the neonates are nourished exclusively on milk and the weaning period when the diet gradually changes to solid food. At early postnatal stages, only a few gustducin- or TRPM5-expressing cells have been found; they display an immature morphology. At the time of weaning, numerous gustducin- or TRPM5-positive cells are present in the gastric mucosa and are isomorphic to adult candidate chemosensory cells. The typical accumulation of gustducin and TRPM5 cells at the border between the forestomach and corpus region and the characteristic tissue fold or "limiting ridge" have not been observed at early postnatal stages but are complete at the time of weaning. The appearance of candidate chemosensory cells at the strategic position occurs within the last few days before weaning but after the formation of the limiting ridge. Thus, both the topographic arrangement of the cells and the limiting ridge seem to be important features for the processing of solid food in the mouse stomach.
... WOLFGANG W. LUEKEN, HEINZ BREER, and MARTINA HARTKEMEYER Arbeitsgruppe Zoophysiologie/Zellphy... more ... WOLFGANG W. LUEKEN, HEINZ BREER, and MARTINA HARTKEMEYER Arbeitsgruppe Zoophysiologie/Zellphysiologie, Universitat Osnabriick, 04500 Osnabriick, West Germany ABSTRACT. ... J. Protozool., 20: 143-145. 11. Luporini, P. Bracchi, P. & Esposito, F. 1979. ...
Changes in the activity of (Na+, K+)-ATPase of synaptosomal membranes induced by exogenous gangli... more Changes in the activity of (Na+, K+)-ATPase of synaptosomal membranes induced by exogenous gangliosides were studied. Depending on the ganglioside-protein ratio, the enzyme activity was finally reduced to 40% when the ratio was about 1. By analysis of the reaction kinetics the effect was characterized as a noncompetitive inhibition. Moreover the ganglioside effect was clearly dependent on the incubation temperature. Since exogenous gangliosides thereby caused a shifting in the optimum temperature of (Na+, K+)-ATPase, the effect is discussed in terms of changes of the membrane properties. In preincubation experiments it was revealed that the interaction of the glycolipids with synaptosomal membranes itself was temperature dependent and enhanced by ATP. It is suggested that ganglioside micelles might have been incorporated by the membranes in a way comparable to a fusion process.
Chemosensory neurons in the olfactory epithelium (OE) project axonal processes to the olfactory b... more Chemosensory neurons in the olfactory epithelium (OE) project axonal processes to the olfactory bulb (OB) of the brain. During embryonic stages, on their trajectory to the OB, the outgrowing axons traverse the so-called cribriform mesenchyme, which is located between the OE and the OB. The molecular cues guiding these axons through the cribriform mesenchyme are largely unknown. To identify molecules influencing the axonal trajectory in the murine cribriform mesenchyme, we performed microarray analyses focusing on extracellular matrix (ECM) proteins present in this tissue. Thereby, the ECM protein Reelin turned out to be an interesting candidate. Reelin was found to be expressed by numerous cells in the cribriform mesenchyme during the embryonic stages when the first axons navigate from the OE to the OB. These cells were closely associated with olfactory axons and apparently lack glial and neuronal markers. In the mesenchyme underlying the OE, localization of the Reelin protein was not confined to the Reelin-expressing cells, but it was also observed to be widely distributed in the ECM-most prominently in regions traversed by olfactory axons. Importantly, these axons were found to be endowed with the Reelin receptor very-low-density lipoprotein receptor (VLDLR). Finally, Reelin expression was also detectable in neuronal cells of the OB, which are contacted by VLDLR-positive olfactory axons. In summary, the results of the present study suggest that a Reelin/VLDLR signaling pathway might contribute to the formation of olfactory projections to the OB and the establishment of initial contacts between the incoming axons and neurons in the OB.
We have solved the crystal structure of aphrodisin, a pheromonal protein inducing a copulatory be... more We have solved the crystal structure of aphrodisin, a pheromonal protein inducing a copulatory behaviour in male hamster, using MAD methods with selenium, at 1.63 A Ê resolution. The monomeric protein belongs to the lipocalin family, and possesses a disul®de bridge in a loop between strands 2 and 3. This disul®de bridge is characteristic of a family of lipocalins mainly identi®ed in rodents, and is analogous to the ®fth disul®de bridge of the long neurotoxins, such as alpha cobratoxin. An elongated electron density was found inside the buried cavity, which might represent a serendipitous ligand of unknown origin. The analysis of the water accessible surfaces of the side-chains bordering the cavity indicates that Phe76 may be the door for the natural ligand to access the cavity. This residue de®nes the entry of the cavity as belonging to the consensus for lipocalins. The face bearing Phe76 might also serve for the interaction with the receptor.
The molecular mechanisms mediating the chemoelectrical signal transduction in olfactory receptor ... more The molecular mechanisms mediating the chemoelectrical signal transduction in olfactory receptor cells are still elusive. In this study odor induced formation of second messengers in rat olfactory cilia was monitored in a subsecond time range using a rapid kinetic device. Application of micromolar concentration of citralva induced a rapid, transient elevation of the cyclic adenosine monophosphate level, whereas the concentration of inositol trisphosphate was not affected. In contrast, pyrazine caused a rise in the concentration of inositol trisphosphate, not affecting the level of cyclic adenosine monophosphate. Analysis of the kinetic parameter for the odorant induced reaction indicated that apparently two systems are operating simultaneously.
Olfactory sensory neurons expressing different members of the mOR37 odourant receptor subfamily s... more Olfactory sensory neurons expressing different members of the mOR37 odourant receptor subfamily send their axons to distinct glomeruli located in the immediate vicinity in the olfactory bulb [Strotmann, J., Conzelmann, S., Beck, A., Feinstein, P., Breer, H. & Mombaerts, P. J. Neurosci., 20, 6927±6938]. In this study, the potential of transgenic mouse lines was used to explore the onset of receptor expression, the outgrowth of axons as well as the glomerulus formation for two neuron populations expressing different mOR37 subtypes. The data indicate a synchronous time course of these features for both neuron populations. From E15 until the day of birth, the axons of the two mOR37 populations terminate in a common, small area of the presumptive olfactory bulb. During a short postnatal phase, the two axon populations segregate into distinct, protoglomerular structures; some aberrant ®bers can still be observed during this period.
Voltage-dependent Ca2+ channels are considered as molecular trigger elements for signal transmiss... more Voltage-dependent Ca2+ channels are considered as molecular trigger elements for signal transmission at chemical synapses. Due to their central role in this fundamental process, function and pharmacology of presynaptic Ca2+ channels have recently been the subject of extensive exploration employing various experimental techniques. Several lines of evidence indicate that, at nerve terminals in higher vertebrates, the evoked influx of Ca2+ -ions is mainly mediated by Ca2+ channels of the P-type. The stringent regulation of presynaptic Ca2+ channels is supposed to be involved in fine-tuning the efficiency of synaptic transmission. Intrinsic control mechanisms, such as voltage- or Ca(2+)-dependent inactivation, or modulation of channel activity, either by G-proteins directly or via phosphorylation by protein kinases, may be of particular functional importance.
The rapid and transient generation of pulses of either cAMP or IP3 is considered the primary reac... more The rapid and transient generation of pulses of either cAMP or IP3 is considered the primary reaction in olfactory signal transduction. There is some recent evidence suggesting that another second messenger system, involving cGMP, may also play an important role in olfactory signalling. High doses of odorant elicit a delayed and sustained elevation of cGMP /evels due to the operation of the nitric oxide (NO) synthase/guanylyl cydase system. The interplay of NO and cGMP is supposed to trigger molecular mechanisms, induding adaptation processes, which enable the olfactory neuroepithe/ium to cope with strong stimuli. Furthermore, a characteristic pattern of staining for NO synthase in the olfactory bulb suggests that the NO/cGMP system may also participate in neuronal processing of the sensory input.
Abstraet--A combination of the stopped-flow technology with dual channel spectrofluorometry of Ca... more Abstraet--A combination of the stopped-flow technology with dual channel spectrofluorometry of Ca 2+indicators was utilized for the measurement of rapid Ca2+-signals in rat cerebral cortical synaptosomes evoked by K+-depolarization. There was no observable contribution of Ca 2 +_ions from intracellular stores to the rise in [Ca2+],. The kinetics of the fast increase in intracellular Ca 2+ concentration was analysed in relation to the depolarization strength. The maximal increase in [Ca2+], and the time course of Ca 2÷channel inactivation were determined for depolarizations obtained by different extracellular K+-concentrations ([K+]o). An apparent threshold was observed at about 18 mM [K+]o; a maximal Ca2+-signal amplitude was estimated at about 40 mM [K +]o. Pharmacological properties of the involved Ca 2+-channels were determined using selective Ca2+-channel blockers (Dihydropyridines, to-Conotoxin, o~-Agatoxins);
Sall3 is a member of a gene family with homology to the spalt gene of Drosophila melanogaster, en... more Sall3 is a member of a gene family with homology to the spalt gene of Drosophila melanogaster, encoding transcription factors, and acts as downstream target of hedgehog. Vertebrate homologues of spalt have been shown to be involved in development of the limbs and nervous system and several organs including the kidney and heart; mutations in the genes are implicated in several human genetic disorders. Recent studies have shown a total loss of olfactory bulb (OB) dopaminergic (DA) neurons in Sall3-null mice. We assume that tyrosine hydroxylase (TH) may be regulated by Sall3 in OB. In this study, we find that Sall3 and TH co-localize in glomerular layer (GL) of OB. Furthermore, we demonstrate a significant induction of the proximal TH promoter transcription activity by Sall3 in dual-luciferase reporter assay and a reduction of TH expression level in Sall3-deficient cell lines. Collectively, these findings support the notion that Sall3 correlates with the expression of TH in mouse OB and may have a role in OB DA neuron development by regulating TH gene expression. The results from this study may advance our understanding of the molecular pathways of OB in the DA neuron development and differentiation.
The responsiveness of isolated olfactory sensory neurons to stimulation with aliphatic aldehydes ... more The responsiveness of isolated olfactory sensory neurons to stimulation with aliphatic aldehydes of varying chain length (5-10 hydrogenated carbon atoms) was investigated by means of Ca(2+ )imaging. More than half the cells examined were responsive to aliphatic aldehydes. Individual cells did not react or reacted to one or multiple aldehydes; in the latter case, cells only reacted to aldehydes of consecutive carbon chain lengths. The largest proportion of cells responded to octanal. It was also demonstrated that a structural difference as small as one hydrogenated carbon atom was detectable by the olfactory neurons. Neurons were increasingly able to discriminate between two aldehydes as the difference in chain length between the two increased. Discrimination between aldehydes with longer carbon chains was reduced. Although the odorants examined belong to a distinct chemical class and differ only slightly in structure, individual olfactory sensory neurons showed quite different recep...
The detection of volatile odorants is supposed to begin with their interaction with soluble bindi... more The detection of volatile odorants is supposed to begin with their interaction with soluble binding proteins which shuttle the hydrophobic ligands through the aqueous mucus layer towards specific odorant receptors in the ciliary membrane of olfactory neurons. A large family of receptors for odorants has been identified recently; individual receptor types are expressed in subsets of cells distributed in distinct zones of the olfactory epithelium. Ligand-receptor interaction triggers a rapid multistep reaction cascade, ultimately leading to an electrical response of the receptor neuron. Olfactory signaling is terminated by phosphorylation of receptors via a negative feedback reaction catalyzed by two types of kinases.
Density measurements made on cholinergic synaptic vesicles from the electric organs of Torpedo ma... more Density measurements made on cholinergic synaptic vesicles from the electric organs of Torpedo marmorata at different osmotic pressures are consistent with the following structural model of the vesicle. The particle behaves like a sphere 80-100 nm in diameter bounded by a semi-permeable membrane. The bulk of its soluble constituents are in true solution at physiological osmolalities. The limiting membrane is approximately 4-5 nm thick, suggesting that it contains large areas of phospholipid bilayer exposed to its bathing medium. The limiting membrane takes up about 26% (v/v) of the particle, a further 34% (v/v) of which is osmotically active water and 31% (v/v) hydrated core material at 800 mosmol/1. The buoyant density of the membrane is 1.132 g . cm-3. The density of the hydrated core material is approximately 1.05 g . cm-3. The membrane is selectively permeable to small molecules when subjected to hypo-osmotic stress. It is proposed that this occurs by the formation of small transient pores in the lipid bilayer of the membrane, which are induced by stretching caused by the osmotic pressure change.
The reception of odorous molecules occurs in chemosensory neurons which encode the strength, dura... more The reception of odorous molecules occurs in chemosensory neurons which encode the strength, duration and quality of odorant stimuli into distinct patterns of afferent neuronal signals which travel along the cells' axons towards the brain where decoding of the olfactory message is initiated. Our understanding of the molecular mechanisms mediating the primary events of odor detection has lagged behind the knowledge about other sensory modalities.
The complex physiology of the gastrointestinal (GI) tract must permanently be adjusted according ... more The complex physiology of the gastrointestinal (GI) tract must permanently be adjusted according to the composition of ingested food, which requires continuous monitoring by appropriate sensory systems. Sensing the dietary constituents is thought to be mediated by chemosensory cells residing in the mucosa of the GI tract. We have examined the appearance and differentiation of candidate chemosensory cells at distinct postnatal stages and visualized cells that express gustducin or TRPM5. Two critical stages have been considered: the suckling period when the neonates are nourished exclusively on milk and the weaning period when the diet gradually changes to solid food. At early postnatal stages, only a few gustducin- or TRPM5-expressing cells have been found; they display an immature morphology. At the time of weaning, numerous gustducin- or TRPM5-positive cells are present in the gastric mucosa and are isomorphic to adult candidate chemosensory cells. The typical accumulation of gustducin and TRPM5 cells at the border between the forestomach and corpus region and the characteristic tissue fold or "limiting ridge" have not been observed at early postnatal stages but are complete at the time of weaning. The appearance of candidate chemosensory cells at the strategic position occurs within the last few days before weaning but after the formation of the limiting ridge. Thus, both the topographic arrangement of the cells and the limiting ridge seem to be important features for the processing of solid food in the mouse stomach.
... WOLFGANG W. LUEKEN, HEINZ BREER, and MARTINA HARTKEMEYER Arbeitsgruppe Zoophysiologie/Zellphy... more ... WOLFGANG W. LUEKEN, HEINZ BREER, and MARTINA HARTKEMEYER Arbeitsgruppe Zoophysiologie/Zellphysiologie, Universitat Osnabriick, 04500 Osnabriick, West Germany ABSTRACT. ... J. Protozool., 20: 143-145. 11. Luporini, P. Bracchi, P. & Esposito, F. 1979. ...
Changes in the activity of (Na+, K+)-ATPase of synaptosomal membranes induced by exogenous gangli... more Changes in the activity of (Na+, K+)-ATPase of synaptosomal membranes induced by exogenous gangliosides were studied. Depending on the ganglioside-protein ratio, the enzyme activity was finally reduced to 40% when the ratio was about 1. By analysis of the reaction kinetics the effect was characterized as a noncompetitive inhibition. Moreover the ganglioside effect was clearly dependent on the incubation temperature. Since exogenous gangliosides thereby caused a shifting in the optimum temperature of (Na+, K+)-ATPase, the effect is discussed in terms of changes of the membrane properties. In preincubation experiments it was revealed that the interaction of the glycolipids with synaptosomal membranes itself was temperature dependent and enhanced by ATP. It is suggested that ganglioside micelles might have been incorporated by the membranes in a way comparable to a fusion process.
Chemosensory neurons in the olfactory epithelium (OE) project axonal processes to the olfactory b... more Chemosensory neurons in the olfactory epithelium (OE) project axonal processes to the olfactory bulb (OB) of the brain. During embryonic stages, on their trajectory to the OB, the outgrowing axons traverse the so-called cribriform mesenchyme, which is located between the OE and the OB. The molecular cues guiding these axons through the cribriform mesenchyme are largely unknown. To identify molecules influencing the axonal trajectory in the murine cribriform mesenchyme, we performed microarray analyses focusing on extracellular matrix (ECM) proteins present in this tissue. Thereby, the ECM protein Reelin turned out to be an interesting candidate. Reelin was found to be expressed by numerous cells in the cribriform mesenchyme during the embryonic stages when the first axons navigate from the OE to the OB. These cells were closely associated with olfactory axons and apparently lack glial and neuronal markers. In the mesenchyme underlying the OE, localization of the Reelin protein was not confined to the Reelin-expressing cells, but it was also observed to be widely distributed in the ECM-most prominently in regions traversed by olfactory axons. Importantly, these axons were found to be endowed with the Reelin receptor very-low-density lipoprotein receptor (VLDLR). Finally, Reelin expression was also detectable in neuronal cells of the OB, which are contacted by VLDLR-positive olfactory axons. In summary, the results of the present study suggest that a Reelin/VLDLR signaling pathway might contribute to the formation of olfactory projections to the OB and the establishment of initial contacts between the incoming axons and neurons in the OB.
We have solved the crystal structure of aphrodisin, a pheromonal protein inducing a copulatory be... more We have solved the crystal structure of aphrodisin, a pheromonal protein inducing a copulatory behaviour in male hamster, using MAD methods with selenium, at 1.63 A Ê resolution. The monomeric protein belongs to the lipocalin family, and possesses a disul®de bridge in a loop between strands 2 and 3. This disul®de bridge is characteristic of a family of lipocalins mainly identi®ed in rodents, and is analogous to the ®fth disul®de bridge of the long neurotoxins, such as alpha cobratoxin. An elongated electron density was found inside the buried cavity, which might represent a serendipitous ligand of unknown origin. The analysis of the water accessible surfaces of the side-chains bordering the cavity indicates that Phe76 may be the door for the natural ligand to access the cavity. This residue de®nes the entry of the cavity as belonging to the consensus for lipocalins. The face bearing Phe76 might also serve for the interaction with the receptor.
The molecular mechanisms mediating the chemoelectrical signal transduction in olfactory receptor ... more The molecular mechanisms mediating the chemoelectrical signal transduction in olfactory receptor cells are still elusive. In this study odor induced formation of second messengers in rat olfactory cilia was monitored in a subsecond time range using a rapid kinetic device. Application of micromolar concentration of citralva induced a rapid, transient elevation of the cyclic adenosine monophosphate level, whereas the concentration of inositol trisphosphate was not affected. In contrast, pyrazine caused a rise in the concentration of inositol trisphosphate, not affecting the level of cyclic adenosine monophosphate. Analysis of the kinetic parameter for the odorant induced reaction indicated that apparently two systems are operating simultaneously.
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