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Unexpected carbohydrate cross-binding by Escherichia coli heat-labile enterotoxin. Recognition of human and rabbit target cell glycoconjugates in comparison with cholera toxin.

Journal article
Authors Karl-Anders Karlsson
Susann Teneberg
Jonas Ångström
A Kjellberg
T R Hirst
Jörgen Bergström
Halina Miller-Podraza
Published in Bioorganic & medicinal chemistry
Volume 4
Issue 11
Pages 1919-28
ISSN 0968-0896
Publication year 1996
Published at Institute of Medical Biochemistry
Pages 1919-28
Language en
Links www.ncbi.nlm.nih.gov/entrez/query.f...
Keywords Animals, Bacterial Toxins, chemistry, metabolism, Carbohydrate Metabolism, Carbohydrate Sequence, Cholera Toxin, chemistry, metabolism, Enterotoxins, chemistry, metabolism, Escherichia coli Proteins, Glycoconjugates, chemistry, metabolism, Humans, Intestines, metabolism, Models, Molecular, Molecular Sequence Data, Protein Binding, Rabbits
Subject categories Chemistry

Abstract

The bacterial protein enterotoxins, cholera toxin (CT) of Vibrio cholerae and heat-labile toxin (LT) of Escherichia coli, induce diarrhea by enhancing the secretory activity of the small intestine of man and rabbit (animal model). This physiological effect is mediated by toxin binding to a glycolipid receptor, the ganglioside GM1, Gal beta 3GalNAc beta 4(NeuAc alpha 3)GAl beta 4Glc beta 1Cer. However, LT, but not CT, was recently shown by us to bind also to paragloboside, Gal beta 4GlcNAc beta 3Gal beta 4Glc beta 1Cer, identified in the target cells. By molecular modeling of this tetrasaccharide in the known binding site of LT, the saccharide-peptide interaction was shown to be limited to the terminal disaccharide (N-acetyllactosamine). This sequence is expressed in many glycoconjugates, and we have therefore assayed glycolipids and glycoproteins prepared from the target tissues. In addition to paragloboside, receptor activity for LT was detected in glycoproteins of human origin and in polyglycosylceramides of rabbit. However, CT bound only to GM1. Two variants of LT with slightly different sequences, human (hLT) and porcine (pLT), were identical in their binding to target glycoproteins and polyglycosylceramides, but different regarding paragloboside, which was positive for pLT but negative for hLT. This difference is discussed on basis of modeling, taking in view the difference at position 13, with Arg in pLT and His in hLT. Although N-acetyllactosamine is differently recognized in form of paragloboside by the two toxin variants, we speculate that this sequence in human glycoproteins and rabbit polyglycosylceramides is the basis for the common binding. Much work remains, however, to clear up up this unexpected sophistication in target recognition.

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