Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

---

Query: EC:4.6.1.2 (guanylate cyclase)
8,497 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We report here the molecular characterization of a recombinant cell line (293-STaR) expressing the heat-stable enterotoxin receptor (STaR) from human intestine. We have compared the 293-STaR cell line with the human colonic cell line T84 that endogenously expresses STa binding sites. Scatchard analysis of displacement binding studies revealed a single STa binding site with an affinity (Ki) of 97 pM in 293-STaR compared with 55 pM in T84 cells. Saturation isotherms of STa binding gave a Kd of 94 pM for the cloned receptor expressed in 293 cells and 166 pM for the receptor present in T84 cells. Kinetic measurements of STa binding to 293-STaR gave an association rate constant, K1, of 2.4 x 10(8) M-1 min-1 and a dissociation rate constant, K2, of 0.016 min-1. The half-time of dissociation was 43 min, and the Kd calculated from the ratio of the kinetic constants was 67 pM. The pH profile of STa binding showed that the number of STa binding sites is increased 3-fold at pH 4.0 compared with pH 7.0, with no effect on binding affinity. A polyclonal antibody directed against the extracellular domain of STaR immunoprecipitated two proteins of approximately 140 and 160 kDa from both 293-STaR and T84 cells. Cross-linking of 125I-STa to 293-STaR cells resulted in the labeling of proteins with a molecular mass of approximately 153, 133, 81, 68, 56, and 49 kDa, the two smallest being the more abundant. Similar results have been reported for the STaR present on rat brush border membranes. These data suggest that the STaR-guanylyl cyclase identified by molecular cloning is the only receptor for STa present in T84 cells.
...
PMID:Characterization of the recombinant human receptor for Escherichia coli heat-stable enterotoxin. 131 5

Intestinal guanylate cyclase mediates the action of the heat-stable enterotoxin to cause a decrease in intestinal fluid absorption and to increase chloride secretion, ultimately causing diarrhea. An endogenous ligand that acts on this guanylate cyclase has not previously been found. To search for a potential endogenous ligand, we utilized T84 cells, a human colon carcinoma-derived cell line, in culture as a bioassay. This cell line selectively responds to the toxin in a very sensitive manner with an increase in intracellular cyclic GMP. In the present study, we describe the purification and structure of a peptide from rat jejunum that activates this enzyme. This peptide, which we have termed guanylin, is composed of 15 amino acids and has the following amino acid sequence, PNTCEICAYAACTGC, as determined by automated Edman degradation sequence analysis and electrospray mass spectrometry. Analysis of the amino acid sequence of this peptide reveals a high degree of homology with heat-stable enterotoxins. Solid-phase synthesis of this peptide confirmed that it stimulates increases in T84 cyclic GMP levels. Guanylin required oxidation for expression of bioactivity and subsequent reduction of the oxidized peptide eliminated the effect on cyclic GMP, indicating a requirement for cysteine disulfide bond formation. Synthetic guanylin also displaces heat-stable enterotoxin binding to cultured T84 cells. Based on these data, we propose that guanylin is an activator of intestinal guanylate cyclase and that it stimulates this enzyme through the same receptor binding region as the heat-stable enterotoxins.
...
PMID:Guanylin: an endogenous activator of intestinal guanylate cyclase. 134 55

Undernutrition in human infants is associated with more prolonged episodes of diarrheal disease. Therefore, we tested the hypothesis that malnutrition prolongs the duration of Escherichia coli heat-stable enterotoxin-induced rat jejunal secretion. At weaning, rats were separated into two groups: malnourished rats were fed 50% of the previous day's intake of the fully fed control group. After approximately 2 wk of pair feeding, when malnourished rats weighed less than or equal to 60% of the full fed control group, we measured the secretory response to heat-stable enterotoxin in ligated jejunal loops. Toxin-induced secretion was equal in both groups until 30 min incubation time, after which net secretion continued to increase in the malnourished group but decreased in the fully fed group. Jejunal brush border membranes prepared from malnourished and fully fed rats demonstrated similar heat-stable enterotoxin receptor density, avidity of binding and guanyl cyclase activation. In both groups, radiolabeled toxin injected into in situ jejunal loops was converted into an altered radioligand unable to bind to brush border membranes. However, in malnourished rats, there was both increased appearance of two additional radioligands that still retained their ability to bind to brush border membranes and persistence of biologically active unlabeled toxin as measured in the suckling mouse bioassay. Our studies demonstrate that reduced or delayed inactivation of heat-stable enterotoxin, with continued presence of active toxin species, may contribute to prolonged secretion in the jejunum of malnourished rats.
...
PMID:The jejunal secretory response to Escherichia coli heat-stable enterotoxin is prolonged in malnourished rats. 134 76

The natriuretic peptide receptors, NPR-A and NPR-B, are two members of the newly described class of receptor guanylyl cyclases. The kinaselike domain of these proteins is an important regulator of the guanylyl cyclase activity. To begin to understand the molecular nature of this type of regulation, we made complete and partial deletions of the kinase domain in NPR-A and NPR-B. We also made chimeric proteins in which the kinase domains of NPR-A and NPR-B were exchanged or replaced with kinase domains from structurally similar proteins. Complete deletion of the kinase homology domain in NPR-A and NPR-B resulted in constitutive activation of the guanylyl cyclase. Various partial deletions of this region produced proteins that had no ability to activate the enzyme with or without hormone stimulation. The kinase homology domain can be exchanged between the two subtypes with no effect on regulation. However, structurally similar kinaselike domains, such as from the epidermal growth factor receptor or from the heat-stable enterotoxin receptor, another member of the receptor guanylyl cyclase family, were not able to regulate the guanylyl cyclase activity correctly. These findings suggest that the kinaselike domain of NPR-A and NPR-B requires strict sequence conservation to maintain proper regulation of their guanylyl cyclase activity.
...
PMID:Conservation of the kinaselike regulatory domain is essential for activation of the natriuretic peptide receptor guanylyl cyclases. 135 Mar 22

Plasma membrane forms of guanylyl cyclase have been shown to function as natriuretic peptide receptors. We describe a new clone (GC-C) encoding a guanylyl cyclase receptor for heat-stable enterotoxin. GC-C encodes a protein containing an extracellular amino acid sequence divergent from that of previously cloned guanylyl cyclases; however, the protein retains the intracellular protein kinase-like and cyclase catalytic domains. Expression of GC-C in COS-7 cells results in high guanylyl cyclase activity. In addition, heat-stable enterotoxin from E. coli, but not natriuretic peptides, causes marked elevations of cyclic GMP and is specifically bound by cells transfected with GC-C. The enterotoxin fails to elevate cyclic GMP in nontransfected cells or in cells transfected with the natriuretic peptide/guanylyl cyclase receptors. These results show that a heat-stable enterotoxin receptor responsible for acute diarrhea is a plasma membrane form of guanylyl cyclase.
...
PMID:Guanylyl cyclase is a heat-stable enterotoxin receptor. 170 94

Heat stable enterotoxins (STs) are low molecular-weight peptides secreted by enterotoxigenic bacteria. One type of these enterotoxins (STa) induces intestinal secretion leading to acute diarrhea by binding to a membrane form of guanylate cyclase. We have isolated a cDNA from a human colonic cell line, T84, encoding for a guanylate cyclase-coupled enterotoxin receptor (STaR). The predicted amino acid sequence of the human STa receptor is 81% identical with the previously cloned enterotoxin receptor (GC-C) from rat intestine. COS-7 cells transiently transfected with the cloned cDNA expressed specific concentration-dependent response to STa as measured by cyclic GMP accumulation and is about 20 times more sensitive to the stimulation by STa than has been shown for GC-C.
...
PMID:Isolation and expression of a guanylate cyclase-coupled heat stable enterotoxin receptor cDNA from a human colonic cell line. 171 70

Guanylin is an endogenous mammalian ligand which binds to guanylate cyclase C (GC-C), the Escherichia coli heat-stable enterotoxin receptor. This interaction results in intestinal Cl- and fluid secretion, which is largely, if not exclusively, mediated through the cystic fibrosis transmembrane regulator (CFTR). Using in situ hybridization, we have previously localized guanylin mRNA to villus epithelial cells of the rat small intestine and to superficial epithelial cells of the rat colon. In the present study, we demonstrate immunoreactive guanylin in a subpopulation of goblet cells in the rat jejunum and ileum. In the colon, there was immunostaining of superficial epithelial cells and goblet cells. The immunohistochemical localization of guanylin parallels the observed distribution of guanylin mRNA. Localization of guanylin in goblet cells leads us to speculate that an in vivo function of guanylin regulated, CFTR-mediated Cl- secretion is to hydrate intestinal mucin.
...
PMID:Immunohistochemical localization of guanylin in the rat small intestine and colon. 773 72

Guanylin is a 15-amino acid peptide hormone that was originally isolated from the jejunum of the rat small intestine and shown to be an endogenous activator of the intestinal heat-stable enterotoxin receptor-guanylyl cyclase. Guanylin is synthesized as a 115-amino acid prohormone, proguanylin, which is processed at a site yet to be determined, into a C-terminal bioactive fragment(s). In order to examine the processing of proguanylin in vitro, we have generated large quantities of the properly folded prohormone by constructing an expression vector that directs its secretion into the periplasmic space of Escherichia coli. The bacterially expressed human proguanylin was then processed to smaller C-terminal fragments by protease digestion. Digestion with trypsin or lysine-C generated C-terminal peptides of different length, which have been purified and characterized. Guanylin-22 and guanylin-32 have binding affinities and biological activities similar to guanylin-15, while guanylin-63 and the entire proguanylin have only minimal bioactivity. Circular dichroism spectroscopy reveals that proguanylin is a stably folded protein containing mostly beta-sheet and beta-turn structure.
...
PMID:Processing and characterization of human proguanylin expressed in Escherichia coli. 790 Nov 99

Enterotoxigenic Escherichia coli elaborate a heat-stable enterotoxin that causes diarrhea in humans and animals. The primary event in the diarrheal cascade is the binding of this enterotoxin to specific receptors on enterocytes and activation of guanylyl cyclase. Two intestinal cell lines, Caco-2 and IEC-6, were tested for the presence of these receptors. Although both cell lines exhibited specific binding, only the Caco-2 cell line responded to heat-stable enterotoxin with increased guanylyl cyclase activity. Cloning and expression studies confirmed that the receptor present in Caco-2 cells is a homologue of guanylyl cyclase C, a known transmembrane heat-stable enterotoxin receptor. Expression of the receptor in differentiating Caco-2 cells increases with cell maturation, indicating that these cells are a suitable model for future studies. However, Northern and polymerase chain reaction analyses demonstrated that guanylyl cyclase C is not expressed in IEC-6 cells, strongly suggesting the presence of a novel heat-stable enterotoxin receptor that is not coupled to guanylyl cyclase activity.
...
PMID:Comparison of receptors for Escherichia coli heat-stable enterotoxin: novel receptor present in IEC-6 cells. 838 96

Guanylyl cyclase (GC) plays a central role in the responses of vertebrate rod and cone photoreceptors to light. cGMP is an internal messenger molecule of vertebrate phototransduction. Light stimulates hydrolysis of cGMP, causing the closure of cGMP-dependent cation channels in the plasma membranes of photoreceptor outer segments. Light also lowers the concentration of intracellular free Ca(2+) and by doing so it stimulates resynthesis of cGMP by guanylyl cyclase. The guanylyl cyclases that couple Ca(2+) to cGMP synthesis in photoreceptors are members of a family of transmembrane guanylyl cyclases that includes atrial natriuretic peptide receptors and the heat-stable enterotoxin receptor. The photoreceptor membrane guanylyl cyclases, RetGC-1 and RetGC-2 (also referred to as GC-E and GC-F), are regulated intracellularly by two Ca(2+)-binding proteins, GCAP-1 and GCAP-2. GCAPs bind Ca(2+) at three functional EF-hand structures. Several lines of biochemical evidence suggest that guanylyl cyclase activator proteins (GCAPs) bind constitutively to an intracellular domain of RetGCs. In the absence of Ca(2+) GCAP stimulates and in the presence of Ca(2+) it inhibits cyclase activity. Proper functioning of RetGC and GCAP is necessary not only for normal photoresponses but also for photoreceptor viability since mutations in RetGC and in GCAP cause photoreceptor degeneration.
...
PMID:Regulation of photoreceptor membrane guanylyl cyclases by guanylyl cyclase activator proteins. 1058 Nov 51


1 2 Next >>

---