Cholera Toxin as a Probe for Membrane Biology.
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ABSTRACT:
SUBMITTER: Kenworthy AK
PROVIDER: S-EPMC8402489 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:Diarrheal disease is a major cause of morbidity and mortality in infants and children worldwide. Evidence has indicated immature human enterocytes and their interaction with bacteria and enterotoxins may account for the noted increased susceptibility of neonates to diarrhea. Our aim was to characterize the developmental difference in cholera toxin (CT)-GM1-mediated endocytosis.We used H4 cells (a fetal human small intestinal epithelial cell line), T84 cells, primary cultured mature human small intestinal epithelial cells, and human fetal small intestine xenografts. In addition, hydrocortisone was used as a potent intestinal trophic factor to induce maturation of the human enterocytes.Here we show an increase in CT-caveolae and a decrease in CT-clathrin colocalization in H4/hydrocortisone compared with H4 cells by electron microscopy. In T84 and freshly isolated human small intestinal epithelial cells, a significant amount of GM1 was partitioned into the lipid rafts. In contrast, there was little CT-GM1/lipid raft association in H4 cells. However, hydrocortisone significantly increased GM1/lipid raft association in H4 cells. Furthermore, we noted an increase in the level of phosphatidylcholine, sphingomyelin, and the ratio of phosphatidylcholine/phosphatidylinositol in mature compared with immature enterocytes and that hydrocortisone can accelerate this maturational process. Disruption of phosphatidylinositol transfer protein alpha using small interference RNA showed an increase in GM1/lipid raft association in H4 cells and resulted in a decreased CT response.Our studies suggest that the developmental change in CT endocytosis is partially caused by an increased GM1-lipid raft association through a maturational change of phospholipid composition on the cell surface of immature enterocytes.
| S-EPMC2587123 | biostudies-literature
Project description:Cholera toxin (CT) causes severe diarrhea by increasing intracellular cAMP leading to a PKA-dependent increase in Cl- secretion through CFTR and decreased Na+ absorption through inhibition of Na+/H+ exchanger 3 (NHE3; also known as SLC9A3). The mechanism(s) by which CT inhibits NHE3 is partially understood, although no drug therapy has been successful at reversing this inhibition. We now describe that CT phosphorylates an amino acid in the PDZ domain of SNX27, which inhibits SNX27-mediated trafficking of NHE3 from the early endosomes to the plasma membrane (PM), and contributes to reduced basal NHE3 activity through a mechanism that involves reduced PM expression and reduced endocytic recycling. Importantly, mutagenesis studies (Ser to Asp) showed that the effect of this phosphorylation of SNX27 phenocopies the effects seen upon loss of SNX27 function, affecting PM trafficking of cargo proteins that bind SNX27-retromer. Additionally, CT destabilizes retromer function by decreasing the amount of core retromer proteins. These effects of CT can be partially rescued by enhancing retromer stability by using 'pharmacological chaperones'. Moreover, pharmacological chaperones can be used to increase basal and cholera toxin-inhibited NHE3 activity and fluid absorption by intestinal epithelial cells.This article has an associated First Person interview with the first author of the paper.
| S-EPMC6127729 | biostudies-literature
Project description:Cholera is a diarrheal disease caused by a protein toxin released by Vibrio cholera in the host's intestine. The toxin enters intestinal epithelial cells after binding to specific carbohydrates on the cell surface. Over recent years, considerable effort has been invested in developing inhibitors of toxin adhesion that mimic the carbohydrate ligand, with particular emphasis on exploiting the multivalency of the toxin to enhance activity. In this review we introduce the structural features of the toxin that have guided the design of diverse inhibitors and summarise recent developments in the field.
| S-EPMC5827775 | biostudies-literature
Project description:Despite the considerable information available with regards to the structure of the clostridial neurotoxins, and their inherent threat as biological warfare agents, the mechanisms underpinning their interactions with and translocation through the cell membrane remain poorly understood. We report herein the results of an in situ scanning probe microscopy study of the interaction of tetanus toxin C-fragment (Tet C) with supported planar lipid bilayers containing the ganglioside receptor G(T1b). Our results show that Tet C preferentially binds to the surface of fluid phase domains within biphasic membranes containing G(T1b) and that with an extended incubation period these interactions lead to dramatic changes in the morphology of the lipid bilayer, including the formation of 40-80 nm diameter circular cavities. Combined atomic force microscopy/total internal reflection fluorescence microscopy experiments confirmed the presence of Tet C in the membrane after extended incubation. These morphological changes were found to be dependent upon the presence of G(T1b) and the solution pH.
| S-EPMC1779908 | biostudies-literature
Project description:Membrane fusion is essential for the transport of macromolecules and viruses across membranes. While glycan-binding proteins (lectins) often initiate cellular adhesion, subsequent fusion events require additional protein machinery. No mechanism for membrane fusion arising from simply a protein binding to membrane glycolipids has been described thus far. Herein, we report that a biotinylated protein derived from cholera toxin becomes a fusogenic lectin upon cross-linking with streptavidin. This novel reengineered protein brings about hemifusion and fusion of vesicles as demonstrated by mixing of fluorescently labeled lipids between vesicles as well as content mixing of liposomes filled with fluorescently labeled dextran. Exclusion of the complex at vesicle-vesicle interfaces could also be observed, indicating the formation of hemifusion diaphragms. Discovery of this fusogenic lectin complex demonstrates that new emergent properties can arise from simple changes in protein architecture and provides insights into new mechanisms of lipid-driven fusion.
| S-EPMC9764410 | biostudies-literature
Project description:AB5 bacterial toxins and polyomaviruses induce membrane curvature as a mechanism to facilitate their entry into host cells. How membrane bending is accomplished is not yet fully understood but has been linked to the simultaneous binding of the pentameric B subunit to multiple copies of glycosphingolipid receptors. Here, we probe the toxin membrane binding and internalization mechanisms by using a combination of superresolution and polarized localization microscopy. We show that cholera toxin subunit B (CTxB) can induce membrane curvature only when bound to multiple copies of its glycosphingolipid receptor, GM1, and the ceramide structure of GM1 is likely not a determinant of this activity as assessed in model membranes. A mutant CTxB capable of binding only a single GM1 fails to generate curvature either in model membranes or in cells, and clustering the mutant CTxB-single-GM1 complexes by antibody cross-linking does not rescue the membrane curvature phenotype. We conclude that both the multiplicity and specific geometry of GM1 binding sites are necessary for the induction of membrane curvature. We expect this to be a general rule of membrane behavior for all AB5 toxins and polyomaviruses that bind glycosphingolipids to invade host cells.
| S-EPMC7334530 | biostudies-literature
Project description:The molecular mechanisms involved in host pathogen interactions at mucosal surfaces needs to be better understood in order to develop immune-mediated methods of protection against pathogens. Cholera toxin (CT) has the rare ability for a protein of inducing robust mucosal immunity in the gut and is therefore an excellent model with which to determine mechanisms of adjuvanticity and immunogenicity at intestinal mucosal surfaces. Jejunal epithelial cells are one of the first sites of antigen encounter. Therefore a porcine intestinal epithelial cell line, IPEC-J2, was cultured in 6-well transwell plates in the presence or absence of 50 ng/ml cholera toxin for up to 8 hours and the cell layer was harvested for gene expression analysis using the Affymetrix porcine genome array and real-time PCR analysis. Affymetrix analysis identified, and real-time PCR analysis of 15 genes confirmed, an increase in gene expression for 59 genes and a decrease in gene expression for 14 genes under CT treatment. An 8 hour time course of expression revealed that by 2-4 hours after CT treatment, all 10 upregulated genes were differentially expressed and by 4-6 hours after CT treatment 3 of the 5 downregulated genes were differentially expressed. These data suggest that the potent mucosal adjuvanticity and immunogenicity of CT derives from rapid alterations in gene expression at the site of first antigen encounter with the immune system. Characterization of early immune gene expression may elucidate potential biological mechanisms for mucosal immune induction leading to the development of effective vaccines against enteric pathogens. Keywords: Treatment comparison, cholera toxin vs untreated at 8h time point
2008-04-01 | GSE10314 | GEO
Project description:Cholera toxin (CTx) is an AB5 cytotonic protein that has medical relevance in cholera and as a novel mucosal adjuvant. Here, we report an analysis of the noncovalent homopentameric complex of CTx B chain (CTx B5) using electrospray ionization triple quadrupole mass spectrometry and tandem mass spectrometry and the analysis of the noncovalent hexameric holotoxin usingelectrospray ionization time-of-flight mass spectrometry over a range of pH values that correlate with those encountered by this toxin after cellular uptake. We show that noncovalent interactions within the toxin assemblies were maintained under both acidic and neutral conditions in the gas phase. However, unlike the related Escherichia coli Shiga-like toxin B5 pentamer (SLTx B), the CTx B5 pentamer was stable at low pH, indicating that additional interactions must be present within the latter. Structural comparison of the CTx B monomer interface reveals an additional alpha-helix that is absent in the SLTx B monomer. In silico energy calculations support interactions between this helix and the adjacent monomer. These data provide insight into the apparent stabilization of CTx B relative to SLTx B.
| S-EPMC1432099 | biostudies-literature
Project description:Cholera toxin (CT) enters and intoxicates host cells after binding cell surface receptors via its B subunit (CTB). We have recently shown that in addition to the previously described binding partner ganglioside GM1, CTB binds to fucosylated proteins. Using flow cytometric analysis of primary human jejunal epithelial cells and granulocytes, we now show that CTB binding correlates with expression of the fucosylated Lewis X (LeX) glycan. This binding is competitively blocked by fucosylated oligosaccharides and fucose-binding lectins. CTB binds the LeX glycan in vitro when this moiety is linked to proteins but not to ceramides, and this binding can be blocked by mAb to LeX. Inhibition of glycosphingolipid synthesis or sialylation in GM1-deficient C6 rat glioma cells results in sensitization to CT-mediated intoxication. Finally, CT gavage produces an intact diarrheal response in knockout mice lacking GM1 even after additional reduction of glycosphingolipids. Hence our results show that CT can induce toxicity in the absence of GM1 and support a role for host glycoproteins in CT intoxication. These findings open up new avenues for therapies to block CT action and for design of detoxified enterotoxin-based adjuvants.
| S-EPMC5825173 | biostudies-literature
Project description:The five B-subunits (CTB5) of the Vibrio cholerae (cholera) toxin can bind to the intestinal cell surface so the entire AB5 toxin can enter the cell. Simultaneous binding can occur on more than one of the monosialotetrahexosylganglioside (GM1) units present on the cell surface. Such simultaneous binding arising from the toxins multivalency is believed to enhance its affinity. Thus, blocking the initial attachment of the toxin to the cell surface using inhibitors with GM1 subunits has the potential to stop the disease. Previously we showed that tetravalent GM1 molecules were sub-nanomolar inhibitors of CTB5. In this study, we synthesized a pentavalent version and compared the binding and potency of penta- and tetravalent cholera toxin inhibitors, based on the same scaffold, for the first time. The pentavalent geometry did not yield major benefits over the tetravalent species, but it was still a strong inhibitor, and no major steric clashes occurred when binding the toxin. Thus, systems which can adopt more geometries, such as those described here, can be equally potent, and this may possibly be due to their ability to form higher-order structures or simply due to more statistical options for binding.
| S-EPMC4603408 | biostudies-literature