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At least 973 records · Page 54Linked to original sources
PubMed1993

Cardiovascular responses of conscious rats to carotid body chemoreceptor stimulation by intravenous KCN.

In the present study we analyzed the cardiovascular, respiratory and behavioral responses evoked in rats by KCN. Hypertension, hyperpnea and alerting behavior were characteristic responses in unanesthetized animals. Selective denervation of aortic and carotid bifurcation areas confirmed the carotid body chemoreceptor (CBC) origin of these responses. Sino-aortic denervation, as well as selective carotid sinus denervation abolished the responses, while, after selective aortic denervation, the responses were not different from those of the control rats. The administration of prazosin abolished the hypertensive response but did not change the bradycardic response, whereas the administration of atropine eliminated the bradycardic response and potentiated the hypertensive response to KCN. Increasing doses of KCN (10-80 micrograms/rat) produced proportionally larger bradycardia, hypertension and hyperventilation. Slight attenuation of bradycardic responses to KCN were observed in rats under chloralose anesthesia, while marked depression of bradycardic responses were observed under pentobarbitone anesthesia. Both anesthetics changed the hypertensive responses to hypotensive responses. In conclusion, the cardiovascular, respiratory and behavioral responses to intravenous KCN are a good functional test to CBC stimulation in unanesthetized rats, producing simultaneously intense bradycardia with hyperventilation and behaviour responses.

Animals↗
PubMed1996

Identification of a gene for a chemoreceptor of the methyl-accepting type in the symbiotic plasmid of Rhizobium leguminosarum bv. viciae UPM791.

The 4 kb DNA region located immediately upstream of the Rhizobium leguminosarum bv. viciae UPM791 hydrogen structural genes was sequenced and found to encode a chemoreceptor of the methyl-accepting type, the first to be described in a rhizobial symbiotic plasmid. Two additional open reading frames were found. Their protein products showed sequence homology to dehydrogenases and isomerases involved in the metabolism of aromatic compounds. Mutant analysis showed that this region is not required for hydrogenase activity.

Amino Acid Sequence↗
PubMed1978

A model for cyclic AMP-chemoreceptor interaction in Dictyostelium discoideum.

Based on the chemotactic activity of approximately 50 different adenosine 3',5'-cyclic-monophosphate (cyclic AMP) derivatives with substitutions at the phosphate, ribose and adenine moieties, a model for the cyclic AMP-chemoreceptor interaction in Dictyostelium discoideum is proposed. In this model the cyclic AMP molecule is bound to the receptor by three hydrogen bonds at, respectively, the 3'-oxygen of the ribose and the 6-amino and the 7-nitrogen of the base, and possibly by one ionic interaction of the negatively charged phosphate group. The conformation of the adenine moiety is in the anti range and binds additionally to the receptor by hydrophobic interactions betueen its pi-electron system and a corresponding acceptor at the active site. Although this receptor clearly differs from that involved in protein kinase activation in higher organisms, the existence of striking similarities suggests a basic mechanism for cyclic AMP interaction conserved during evolution.

Binding Sites↗
PubMed2005

Collaborative signaling by bacterial chemoreceptors.

Motile bacteria seek optimal living habitats by following gradients of attractant and repellent chemicals in their environment. The signaling machinery for these chemotactic behaviors, although assembled from just a few protein components, has extraordinary information-processing capabilities. Escherichia coli, the best-studied model, employs a networked cluster of transmembrane receptors to detect minute chemical stimuli, to integrate multiple and conflicting inputs, and to generate an amplified output signal that controls the cell's flagellar motors. Signal gain arises through cooperative action of chemoreceptors of different types. The signaling-teams within a receptor cluster may be built from trimers of receptor dimers that communicate through shared connections to their partner signaling proteins.

Chemotaxis↗
PubMed2001

Site-directed solid-state NMR measurement of a ligand-induced conformational change in the serine bacterial chemoreceptor.

The challenging nature of studies of membrane proteins has made it difficult to determine the molecular mechanism of transmembrane signaling. For the bacterial chemoreceptor family, there are crystal structures of the internal and external domains, structural models of the transmembrane domain, and evidence for subtle ligand-induced conformational changes, but the signaling mechanism remains controversial. We have used a novel site-directed solid-state NMR distance measurement approach, using (13)C(19)F REDOR, to measure a ligand-induced change of 1.0 +/- 0.3 A in the distance between helices alpha 1 and alpha 4 of the ligand-binding domain in the intact, membrane-bound serine receptor. This distance change is shown not to be due to motion of the side chain and thus is due to motion of either the alpha 1 or the alpha 4 helix. Additional distance measurements can be used to determine the type of backbone motion and to follow it to the cytoplasm, to test and refine current proposals for the mechanism of transmembrane signaling. This is a promising general method for high-resolution measurements of local structure in intact, membrane-bound proteins.

Bacterial Proteins↗
PubMed2001

Signalling substitutions in the periplasmic domain of chemoreceptor Trg induce or reduce helical sliding in the transmembrane domain.

We used in vivo oxidative cross-linking of engineered cysteine pairs to assess conformational changes in the four-helix transmembrane domain of chemoreceptor Trg. Extending previous work, we searched for and found a fourth cross-linking pair that spanned the intrasubunit interface between transmembrane helix 1 (TM1) and its partner TM2. We determined the effects of ligand occupancy on cross-linking rate constants for all four TM1-TM2 diagnostic pairs in conditions that allowed the formation of receptor-kinase complexes for the entire cellular complement of Trg. Occupancy altered all four rates in a pattern that implicated sliding of TM2 relative to TM1 towards the cytoplasm as the transmembrane signalling movement in receptor-kinase complexes. Transmembrane signalling can be reduced or induced by single amino acid substitutions in the ligand-binding region of the periplasmic domain of Trg. We determined the effects of these substitutions on conformation in the transmembrane domain and on ligand-induced changes using the diagnostic TM1-TM2 cysteine pairs. Effects on rates of in vivo cross-linking showed that induced signalling substitutions altered the relative positions of TM1 and TM2 in the same way as ligand binding, and reduced signalling substitutions blocked or attenuated the ligand-induced shift. These results provide strong support for the helical sliding model of transmembrane signalling.

Amino Acid Substitution↗
PubMed2005

Insights into the organization and dynamics of bacterial chemoreceptor clusters through in vivo crosslinking studies.

The team signaling model for bacterial chemoreceptors proposes that receptor dimers of different detection specificities form mixed trimers of dimers that bind the cytoplasmic proteins CheA and CheW to form ternary signaling complexes clustered at the cell poles. We used a trifunctional crosslinking reagent targeted to cysteine residues in the aspartate (Tar) and serine (Tsr) receptors to obtain in vivo snapshots of trimer composition in the receptor population. To analyze the dynamics of trimer formation, we followed the appearance of mixed trimers when cells expressing Tar were induced for the expression of Tsr and treated with the crosslinker shortly after the onset of induction. In the absence of CheA or CheW, preformed Tar trimers exchanged partners readily with newly made Tsr. Conversely, in the presence of CheA and CheW, receptor trimers seldom exchanged partners, irrespective of the presence or absence of attractants. The C-terminal receptor-coupling domain of the CheA kinase, which contains binding determinants for the CheW protein, was essential for conferring low exchangeability to the preformed trimers of dimers. CheW also was required for this effect, but, unlike CheA, overexpression of CheW interfered with trimer formation and chemotactic behavior. The CheW effect probably occurs through binding interactions that mask the receptor sites needed for trimer formation. We propose that clustered receptors are organized in mixed trimers of dimers through binding interactions with CheA and CheW, which play distinctly different architectural roles. Moreover, once complete signaling teams have formed, they no longer undergo dynamic exchange of receptor members.

Bacterial Proteins↗
PubMed2006

Osmotic stress mechanically perturbs chemoreceptors in Escherichia coli.

Two-component signaling systems play a major role in the long-term adaptation of microorganisms to changes in osmolarity, but how osmoreceptors work is not well understood. Temporal changes in solute concentration are sensed by the chemotaxis system in Escherichia coli, enabling these bacteria to avoid regions of high osmolarity. To study how osmolarity is detected in this system, we fused yellow fluorescent protein (YFP) to the C terminus of the serine or aspartate chemoreceptor, monitored the steady-state fluorescence polarization of YFP, and found that the polarization decreased substantially upon addition of osmotic agents. This decrease was due to an increase in fluorescence resonance energy transfer between YFP fluorophores in adjacent homodimers within trimers of dimers. Thus, changes in homodimer spacing and/or orientation appear to initiate osmotactic signaling.

Escherichia coli K12↗
PubMed1989

An Escherichia coli chemoreceptor gene is temporally controlled in Caulobacter.

Flagellar and chemotaxis genes are transcribed at a discrete time in the Caulobacter cell cycle. We demonstrate here that the expression of the Escherichia coli chemoreceptor gene tsr, with 2.6 kilobases of its upstream sequence, is temporally controlled in Caulobacter crescentus. The tsr gene was placed on the chromosome in single copy or on a low-copy-number plasmid. It was found that the Tsr protein appeared at the same point in the cell cycle as an endogenous C. crescentus methyl-accepting chemotaxis protein. Nuclease S1 mapping experiments showed that the tsr transcript was also controlled by the cell cycle, suggesting that the E. coli tsr gene is regulated by C. crescentus factors that mediate the timing of transcription initiation. The apparent transcription start site of the E. coli tsr gene was determined in both E. coli and C. crescentus, and we found that in both backgrounds the promoter used conforms to the consensus sequence for the promoters of the flagellar and chemosensory genes of Bacillus subtilis and E. coli. The use of this promoter suggests that C. crescentus has a cognate sigma factor and predicts that other C. crescentus genes are expressed from this consensus promoter.

Bacteria↗
PubMed1997

The Aer protein and the serine chemoreceptor Tsr independently sense intracellular energy levels and transduce oxygen, redox, and energy signals for Escherichia coli behavior.

We identified a protein, Aer, as a signal transducer that senses intracellular energy levels rather than the external environment and that transduces signals for aerotaxis (taxis to oxygen) and other energy-dependent behavioral responses in Escherichia coli. Domains in Aer are similar to the signaling domain in chemotaxis receptors and the putative oxygen-sensing domain of some transcriptional activators. A putative FAD-binding site in the N-terminal domain of Aer shares a consensus sequence with the NifL, Bat, and Wc-1 signal-transducing proteins that regulate gene expression in response to redox changes, oxygen, and blue light, respectively. A double mutant deficient in aer and tsr, which codes for the serine chemoreceptor, was negative for aerotaxis, redox taxis, and glycerol taxis, each of which requires the proton motive force and/or electron transport system for signaling. We propose that Aer and Tsr sense the proton motive force or cellular redox state and thereby integrate diverse signals that guide E. coli to environments where maximal energy is available for growth.

Amino Acid Sequence↗
PubMed2006

Differential recognition of citrate and a metal-citrate complex by the bacterial chemoreceptor Tcp.

The chemoreceptor Tcp of Salmonella enterica serovar Typhimurium can sense citrate and a metal-citrate complex as distinct attractants. In this study, we tried to investigate the molecular mechanism of this discrimination. That citrate binds directly to Tcp was verified by the site-specific thiol modification assays using membrane fractions prepared from Escherichia coli cells expressing the mutant Tcp receptors in which single Cys residues were introduced at positions in the putative ligand-binding pocket. To determine the region responsible for the ligand discrimination, we screened for mutations defective in taxis to magnesium in the presence of citrate. All of the isolated mutants from random mutagenesis with hydroxylamine were defective in both citrate and metal-citrate sensing, and the mutated residues are located in or near the alpha1-alpha2 and alpha3-alpha4 loops within the periplasmic domain. Further analyses with site-directed replacements around these regions demonstrated that the residue Asn(67), which is presumed to lie at the subunit interface of the Tcp homodimer, plays a critical role in the recognition of the metal-citrate complex but not that of citrate. Various amino acids at this position differentially affect the citrate and metal-citrate sensing abilities. Thus, for the first time, the abilities to sense the two attractants were genetically dissected. Based on the results obtained in this study, we propose models in which the discrimination of the metal-citrate complex from citrate involves cooperative interaction at Asn(67) and allosteric switching.

Allosteric Regulation↗
PubMed1998

Flux detectors versus concentration detectors: two types of chemoreceptors.

Dose-response curves relating the external stimulus concentration to receptor occupancy differ in two types of chemoreceptor organs. In 'concentration detectors' the receptor molecules at the receptor cell membrane are directly exposed to the external stimulus concentration; these organs exhibit the well-known hyperbolic dose-response relationship reflecting the association-dissociation of stimulus and receptor molecules. In contrast, 'flux detectors' accumulate the stimulus molecules in a perireceptor compartment. In flux detectors, deactivation of stimulus molecules may be in balance with arrival, as a prerequisite for producing a constant effective stimulus concentration at constant adsorptive flux of stimulus molecules. In a simple model of a flux detector in which receptor molecules themselves catalyze the deactivation, the dose-response relationship is linear. It reflects the rate of stimulus deactivation. If the deactivation is catalyzed by a separate enzyme, the dose-response relationship can be close to hyperbolic, or linear. In all cases, the receptor molecules are maximally occupied if the adsorptive flux equals or exceeds the maximum rate of stimulus deactivation. The time course of the receptor potential recorded from moths' pheromone receptors depends on the odor compound, which suggests that a peripheral process, possibly the stimulus deactivation, is the slowest, rate-limiting process of the transduction cascade. Further evidence comes from experiments with stimuli oversaturating the mechanism responsible for the decline of the receptor potential.

Catalysis↗
PubMed1992

Effect of the repellent deet on the antennal chemoreceptors for oviposition in Aedes aegypti (Diptera: Culicidae).

The insect repellent, N,N-diethyl-m-toluamide (deet), interferes with detection of the host attractant, lactic acid (LA), by LA-excited neurons on the antennae of female Aedes aegypti (L.) mosquitoes. In the current laboratory behavioral experiment, the attraction of gravid female mosquitoes to a source of ethyl propionate, an oviposition attractant, was reduced by a factor of two when deet was present. Similarly, when deet was presented together with ethyl propionate in electrophysiological experiments, sensitivity of the neural response to ethyl propionate was depressed in a transient, dose-dependent manner that could account for the reduction in behavioral attraction of gravid females to ethyl propionate. Electrophysiologically, the sensitivity of oviposition attractant receptors to ethyl propionate on gravid females was not different from that on nongravid host-seeking females. The similarity between the depression of sensitivity of the oviposition attractant-sensitive neurons induced by deet and that observed in the host attractant-sensitive neurons suggest a common mode of action of deet on peripheral chemoreceptor neurons that mediate these behaviors.

Aedes↗
PubMed1992

Polar localization of a bacterial chemoreceptor.

The bacterial chemotaxis signal transducer MCP is an integral membrane receptor protein. The chemoreceptor is localized at the flagellum-bearing pole of Caulobacter crescentus swarmer cells. Amino-terminal sequences of the MCP target the protein to the membrane while the carboxy-terminal portion of the protein is responsible for polar localization. The C. crescentus and Escherichia coli MCPs have highly conserved carboxy-terminal domains, and when an E. coli MCP is expressed in C. crescentus, it is targeted to the swarmer cell progeny. These results suggest that subcellular localization of a prokaryotic protein involves interaction of specific regions of the protein with unique cell sites that contain either localized binding proteins or a specific secretory apparatus.

Amino Acid Sequence↗
PubMed1981

Emetic action of xylazine on the chemoreceptor trigger zone for vomiting in cats.

Xylazine is an effective sedative analgesic that induces vomiting in the cat. A consistently effective intramuscular emetic dose of xylazine was established in normal cats in this laboratory. Animals in which the area postrema of the medulla oblongata had been chronically destroyed did not exhibit emesis in response to the standard test dose of xylazine but continued to show sedation. By contrast, sham-operated cats responded normally. Refractoriness to deslanoside, a known specific emetic drug, was used as functional proof for successful ablation of area postrema, and the lesions were also validated histologically. We conclude that xylazine exerts its emetic action on the chemoreceptor trigger zone of the area postrema. It is suggested that this action may be mediated by an opiate type of molecular receptors.

Animals↗
PubMed2004

Analysis of the Frz signal transduction system of Myxococcus xanthus shows the importance of the conserved C-terminal region of the cytoplasmic chemoreceptor FrzCD in sensing signals.

The Frz chemosensory system controls directed motility in Myxococcus xanthus by regulating cellular reversal frequency. M. xanthus requires the Frz system for vegetative swarming on rich media and for cellular aggregation during fruiting body formation on starvation media. The Frz signal transduction pathway is formed by proteins that share homology with chemotaxis proteins from enteric bacteria, which are encoded in the frzA-F putative operon and the divergently transcribed frzZ gene. FrzCD, the Frz system chemoreceptor, contains a conserved C-terminal module present in methyl-accepting chemotaxis proteins (MCPs); but, in contrast to most MCPs, FrzCD is localized in the cytoplasm and the N-terminal region of FrzCD does not contain transmembrane or sensing domains, or even a linker region. Previous work on the Frz system was limited by the unavailability of deletion strains. To understand better how the Frz system functions, we generated a series of in-frame deletions in each of the frz genes as well as regions encoding the N-terminal portion of FrzCD. Analysis of mutants containing these deletions showed that FrzCD (MCP), FrzA (CheW) and FrzE (CheA-CheY) control vegetative swarming, responses to repellents and directed movement during development, thus constituting the core components of the Frz pathway. FrzB (CheW), FrzF (CheR), FrzG (CheB) and FrzZ (CheY-CheY) are required for some but not all responses. Furthermore, deletion of approximately 25 amino acids from either end of the conserved C-terminal region of FrzCD results in a constitutive signalling state of FrzCD, which induces hyper-reversals with no net cell movement. Surprisingly, deletion of the N-terminal region of FrzCD shows only minor defects in swarming. Thus, signal input to the Frz system must be sensed by the conserved C-terminal module of FrzCD and not the usual N-terminal region. These results indicate an alternative mechanism for signal sensing with this cytoplasmic MCP.

Bacterial Proteins↗
PubMed1999

Selective modulation of membrane currents by hypoxia in intact airway chemoreceptors from neonatal rabbit.

1. We previously described voltage-dependent ionic currents and hypoxia chemosensitivity in cultured pulmonary neuroepithelial body (NEB) cells isolated from fetal rabbit. Here we use fresh neonatal rabbit lung slices (200-400 micrometer thick) to characterize the electrophysiological properties of 'intact' NEBs with patch-clamp, whole-cell recording. 2. Under voltage clamp, outward currents were partially inhibited by TEA (20 mM), 4-amino pyridine (4-AP; 2 mM) and cadmium (Cd2+; 100 micrometer), suggesting the presence of both Ca2+-dependent (IK(Ca)) and Ca2+-independent (IK(V)) components. 3. Inward currents, carried by voltage-dependent Ca2+ channels and also, in occasional cells (approximately 11%), by TTX-sensitive Na+ channels, were also detected in intact NEB cells. 4. Hypoxia (PO2 = 15-20 mmHg) reduced the outward K+ current by approximately 34% during voltage steps from -60 to +30 mV, while inward Ca2+ or Na+ currents were not affected by hypoxia. Hypoxia suppressed roughly equally both IK(Ca) and IK(V) components of outward current, and no further inhibition of K+ currents was seen with either TEA and 4-AP + hypoxia. 5. Diphenylene iodonium (DPI; 1 microM) suppressed outward K+ current by approximately 42%, and DPI + hypoxia had no additional effect on the K+ current. 6. Direct application of H2O2 augmented outward K+ current; for a voltage step from -60 mV to +30 mV, 0.25 mM H2O2 increased K+ current by approximately 37%. 7. These results indicate that intact neonatal NEB cells express hypoxic chemosensitivity and introduce the rabbit lung slice preparation as an new model for investigating the role of airway O2 chemoreceptors.

4-Aminopyridine↗