Escherichia coli STb toxin binding to sulfatide and its inhibition by carragenan

Escherichia coli heat-STb is an important cause of diarrhea in piglets. STb was shown to interact specifically with sulfatide (3′-sulfogalactosyl-ceramide) present on the surface of epithelial cells of piglet jejunum. Basic data are lacking on STb binding to sulfatide in solution and more precisely on the possible inhibition of this interaction. Using surface plasmon resonance technology, we compare binding of STb to sulfatide and other glycoshingolipids previously shown, with a multiplate-binding assay, to also interact to various degrees with the enterotoxin. In addition, inhibition of STb-sulfatide binding was studied using free galactose, galactose-sulfate residues and a polymer of sulfated galactans known as carragenan. We determined a dissociation constant of 2.4±0.61 nM for the STb-sulfatide interaction. These data indicated that STb was binding to sulfatide with greater affinity than previously determined using radiolabeled toxin. Much lower affinities were observed for lactoceramide and glucoceramide. The binding of STb to sulfatide was clearly inhibited by λ-carragenan but not by galactose, 4-SO4-galactose or 6-SO4-galactose. Inhibition of STb binding to its receptor was achieved using λ-carragenan at picomolar concentrations. Then, using IPEC-J2 cells in culture and flow cytometry, we showed that λ-carragenan was able to inhibit the permeabilization process associated with STb.