title: Characterization of the receptor for cholera toxin and Escherichia coli heat-labile toxin in rabbit intestinal brush borders.
abstract: 125I-labelled heat-labile toxin (from Escherichia coli) and 125I-labelled cholera toxin bound to immobilized ganglioside GM1 and Balb/c 3T3 cell membranes with identical specificities, i.e. each toxin inhibited binding of the other. Binding of both toxins to Balb/c 3T3 cell membranes was saturable, with 50% of maximal binding occurring at 0.3 nM for cholera toxin and 1.1 nM for heat-labile toxin, and the number of sites for each toxin was similar. The results suggest that both toxins recognize the same receptor, namely ganglioside GM1. In contrast, binding of 125I-heat-labile toxin to rabbit intestinal brush borders at 0 degree C was not inhibited by cholera toxin, although heat-labile toxin inhibited 125I-cholera toxin binding. In addition, there were 3-10-fold more binding sites for heat-labile toxin than for cholera toxin. At 37 degrees C cholera toxin, but more particularly its B-subunit, did significantly inhibit 125I-heat-labile toxin binding. Binding of 125I-cholera toxin was saturable, with 50% maximal of binding occurring at 1-2 nM, and was quantitatively inhibited by 10(-8) M unlabelled toxin or B-subunit. By contrast, binding of 125I-heat-labile toxin was non-saturable (up to 5 nM), and 2 X 10(-7) M unlabelled B-subunit was required to quantitatively inhibit binding. Neuraminidase treatment of brush borders increased 125I-cholera toxin but not heat-labile toxin binding. Extensive digestion of membranes with Streptomyces griseus proteinase or papain did not decrease the binding of either toxin. The additional binding sites for heat-labile toxin are not gangliosides. Thin-layer chromatograms of gangliosides which were overlayed with 125I-labelled toxins showed that binding of both toxins was largely restricted to ganglioside GM1. However, 125I-heat-labile toxin was able to bind to brush-border galactoproteins resolved by SDS/polyacrylamide-gel electrophoresis and transferred to nitrocellulose.
mesh_terms: D000818:Animals; D001427:Bacterial Toxins / Q000378:metabolism*; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D010450:Endopeptidases / Q000494:pharmacology; D004768:Enterotoxins / Q000378:metabolism*; D029968:Escherichia coli Proteins; D005677:G(M1) Ganglioside / Q000378:metabolism; D006162:Guanylate Cyclase; D007421:Intestine, Small / Q000187:drug effects / Q000378:metabolism*; D008871:Microvilli / Q000187:drug effects / Q000378:metabolism; D009439:Neuraminidase / Q000494:pharmacology; D011817:Rabbits; D011956:Receptors, Cell Surface; D000074261:Receptors, Enterotoxin; D050705:Receptors, Guanylate Cyclase-Coupled; D011971:Receptors, Immunologic / Q000378:metabolism*; D018000:Receptors, Peptide
chemical_list: D001427:Bacterial Toxins; D004768:Enterotoxins; D029968:Escherichia coli Proteins; D011956:Receptors, Cell Surface; D011971:Receptors, Immunologic; D018000:Receptors, Peptide; C023552:choleragen receptor; D005677:G(M1) Ganglioside; C027538:heat-labile enterotoxin, E coli; D009439:Neuraminidase; D010450:Endopeptidases; D006162:Guanylate Cyclase; D000074261:Receptors, Enterotoxin; D050705:Receptors, Guanylate Cyclase-Coupled