Comparison of the carbohydrate-binding specificities of cholera toxin and Escherichia coli heat-labile enterotoxins LTh-I, LT-IIa, and LT-IIb

Infect Immun. 1988 Jul;56(7):1748-53. doi: 10.1128/IAI.56.7.1748-1753.1988.

Abstract

The heat-labile enterotoxins of Vibrio cholerae and Escherichia coli are related in structure and function. They are oligomers consisting of A and B polypeptide subunits. They bind to gangliosides, and they activate adenylate cyclase. The toxins form two antigenically distinct groups; members of each group cross-react but are not necessarily identical. Serogroup I includes cholera toxin (CT) and type I heat-labile enterotoxin (LT-I) of E. coli. LTh-I and LTp-I are antigenic variants of LT-I produced by strains of E. coli from humans and pigs, respectively. Serogroup II contains the type II heat-labile enterotoxin (LT-II) of E. coli. Two antigenic variants designated LT-IIa and LT-IIb have been described. The binding of CT, LTh-I, LT-IIa, and LT-IIb to gangliosides was analyzed by immunostaining thin-layer chromatograms and by solid-phase radioimmunoassay. The four toxins have different glycolipid-binding specificities. LTh-I and CT bind strongly to ganglioside GM1 and less strongly to ganglioside GD1b. However, LTh-I, unlike CT, also binds weakly to GM2 and asialo GM1. LTh-I, like CT, probably binds to the terminal sugar sequence Gal beta 1-3GalNAc beta 1-4(NeuAc alpha 2-3)Gal . . ., where GalNAc is N-acetylgalactosamine and NeuAc is N-acetylneuraminic acid. LT-IIa probably binds to the same sugar sequence to which CT and LTh-I bind, with the additional contribution to binding of a second NeuAc as in GD1b and GD2. Also, LT-IIa must bind the Gal beta 1-3GalNAc . . . sequence in such a way that its binding is relatively unaffected by attachment of NeuAc to the terminal galactose residue as in GD1a, GT1b, and GQ1b. LT-IIb probably binds to the terminal sugar sequence NeuAc alpha 2-3Gal beta 1-4GalNAc . . ., as it binds to gangliosides GD1a and GT1b but not to GM1.

Publication types

  • Comparative Study
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Adrenal Glands / cytology
  • Animals
  • Bacterial Toxins / metabolism*
  • Brain
  • Carbohydrate Conformation
  • Cattle
  • Cholera Toxin / metabolism*
  • Enterotoxins / metabolism*
  • Escherichia coli / metabolism*
  • Escherichia coli Proteins*
  • Fetus
  • G(M1) Ganglioside*
  • Glycolipids / metabolism*
  • Glycosphingolipids / metabolism
  • Mice
  • Neuraminidase
  • Receptors, Cell Surface*
  • Receptors, Immunologic / analysis*
  • Receptors, Immunologic / drug effects
  • Structure-Activity Relationship

Substances

  • Bacterial Toxins
  • Enterotoxins
  • Escherichia coli Proteins
  • Glycolipids
  • Glycosphingolipids
  • Receptors, Cell Surface
  • Receptors, Immunologic
  • glycolipid receptor
  • heat-labile enterotoxin, E coli
  • G(M1) Ganglioside
  • asialo GM1 ganglioside
  • Cholera Toxin
  • Neuraminidase