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.

Bacillus anthracisEdema Toxin Acts as an Adjuvant for Mucosal Immune Responses to Nasally Administered Vaccine Antigens

“…The B subunits of CT and LT-I bind to GM1 gangliosides on target cells (24), while the more promiscuous B subunit of LT-I also exhibits affinity for GM2 and asialo-GM1 (25)(26)(27). CT and LT-I are the best described mucosal adjuvants and both promote mucosal secretory IgA (S-IgA) and plasma Ab responses to coadministered vaccine Ags.…”

Escherichia coli STb toxin induces apoptosis in intestinal epithelial cell lines

“…In order to cause diarrhea, LT first binds the GM1 ganglioside present at the surface of enterocytes via the B subunits (Griffiths et al, 1986, Tsuji et al, 1985. Receptor binding is followed by internalization of LT into vesicles which are retrograde transported to the Golgi apparatus and endoplasmic reticulum (Rappuoli et al, 1999).…”

Les récepteurs des entérotoxines bactériennes

“…De nombreuses études ont montré que CT reconnaissait un récepteur spécifique unique, le glycolipide GM1 (Fig. 2), à la surface de nombreuses cellules et induisait une élévation du taux d'AMPc proportionnel au nombre de sites reconnus [26,40,41,56,67,156].…”

“…coli reconnaît égale-ment le récepteur membranaire GM1, par l'intermédiaire de ses sous-unités B, et conduit aux mêmes effets dans les cellules et dans l'intestin que la toxine CT [56,65,133,136]. Alors que la toxine CT s'attache au GM1 avec une grande sélectivité, la toxine LT fixe d'autres récepteurs membranaires, non reconnus par CT, et qui sont fonctionnels pour LT [55,67,116,134,166].…”