Characterisation of the binding sites for Escherichia coli heat-labile toxin type I in intestinal brush borders.
Intestinal brush borders from Wistar rats contained a total of 20-30-times more binding sites for Escherichia coli heat-labile enterotoxin (LT-1) than for cholera toxin (CT). The results suggest that LT-1 binds to sites in addition to ganglioside GM1, the binding site for CT. Brush border proteins were separated by SDS-PAGE, blotted to nitrocellulose and the filters incubated with 125I-labeled toxins. [125I]LT-1 was shown to bind to a series of brush border galactoproteins ranging in size from 130-140 kDa. Binding was inhibited by unlabeled LT-1 (but not CT), and by ricin and free galactose. A number of brush border enzymes are large glycoproteins which can be solubilised by papain. The papain-solubilised sucrase-isomaltase complex was purified by affinity chromatography and shown to bind LT-1, as did the proteins in fractions enriched in maltase activity. However, such brush border galactoproteins do not account for all of the additional LT-1 binding sites. Thus, brush borders prepared from 1-15-day-old rabbits contained many more binding sites for LT-1 than CT despite the absence of any sucrase-isomaltase activity, and no [125I]LT-1 binding proteins could be detected by blotting. There was a marked variation in the number of LT-1 binding sites in different strains of rat, and between different species.
Department of Biochemistry, University of Leicester, U.K.
S L
SL
Griffiths
D R
DR
Critchley
D000818:Animals; D001427:Bacterial Toxins / Q000737:chemistry*; D001665:Binding Sites; D002772:Cholera Toxin / Q000737:chemistry; D004285:Dogs; D004768:Enterotoxins / Q000737:chemistry*; D004926:Escherichia coli / Q000737:chemistry*; D029968:Escherichia coli Proteins; D006023:Glycoproteins / Q000737:chemistry; D006801:Humans; D007421:Intestine, Small / Q000201:enzymology / Q000648:ultrastructure; D008871:Microvilli / Q000737:chemistry* / Q000201:enzymology; D051381:Rats; D011919:Rats, Inbred Strains; D013045:Species Specificity; D013394:Sucrase-Isomaltase Complex / Q000302:isolation & purification
D001427:Bacterial Toxins; D004768:Enterotoxins; D029968:Escherichia coli Proteins; D006023:Glycoproteins; C017336:galactoproteins; D002772:Cholera Toxin; C027538:heat-labile enterotoxin, E coli; D013394:Sucrase-Isomaltase Complex