Comparison of the glycolipid-binding specificities of cholera toxin and porcine Escherichia coli heat-labile enterotoxin: identification of a receptor-active non-ganglioside glycolipid for the heat-labile toxin in infant rabbit small intestine.
The binding specificities of cholera toxin and Escherichia coli heat-labile enterotoxin were investigated by binding of 125I-labelled toxins to reference glycosphingolipids separated on thin-layer chromatograms and coated in microtitre wells. The binding of cholera toxin was restricted to the GM1 ganglioside. The heat-labile toxin showed the highest affinity for GM1 but also bound, though less strongly, to the GM2, GD2 and GD1b gangliosides and to the non-acid glycosphingolipids gangliotetraosylceramide and lactoneotetraosylceramide. The infant rabbit small intestine, a model system for diarrhoea induced by the toxins, was shown to contain two receptor-active glycosphingolipids for the heat-labile toxin, GM1 ganglioside and lactoneotetraosylceramide, whereas only the GM1 ganglioside was receptor-active for cholera toxin. Preliminary evidence was obtained, indicating that epithelial cells of human small intestine also contain lactoneotetraosylceramide and similar sequences. By computer-based molecular modelling, lactoneotetraosylceramide was docked into the active site of the heat-labile toxin, using the known crystal structure of the toxin in complex with lactose. Interactions which may explain the relatively high toxin affinity for this receptor were found.
Teneberg
S
S
Department of Medical Biochemistry and Microbiology, Göteborg University, Sweden.
Hirst
T R
TR
Angström
J
J
Karlsson
K A
KA
D000818:Animals; D001427:Bacterial Toxins / Q000378:metabolism*; D001665:Binding Sites; D002240:Carbohydrate Sequence; D002772:Cholera Toxin / Q000378:metabolism*; D004768:Enterotoxins / Q000378:metabolism*; D004926:Escherichia coli / Q000378:metabolism*; D029968:Escherichia coli Proteins; D005677:G(M1) Ganglioside / Q000378:metabolism; D006028:Glycosphingolipids / Q000378:metabolism*; D007421:Intestine, Small / Q000378:metabolism*; D008969:Molecular Sequence Data; D011817:Rabbits; D013552:Swine
D001427:Bacterial Toxins; D004768:Enterotoxins; D029968:Escherichia coli Proteins; D006028:Glycosphingolipids; D005677:G(M1) Ganglioside; D002772:Cholera Toxin; C027538:heat-labile enterotoxin, E coli