Enhanced binding of enterotoxigenic Escherichia coli K99 to amide derivatives of the receptor ganglioside NeuGc-GM3.

A natural receptor in pig small intestine [Teneberg, S., Willemsen, P., de Graaf, F. K., & Karlsson, K.-A. (1990) FEBS Lett. 263, 10-14] for the enterotoxigenic bacteria Escherichia coli K99 is the ganglioside NeuGc-GM3 (NeuGc alpha 3Gal beta 4Glc beta Cer) [e.g., H. Smit, W. Gaastra, J. P. Kamerling, J. F. G. Vliegenthart, & F. K. de Graaf (1984) Infect. Immun. 46, 578-584]. Chemical modifications of the carboxyl group of this ganglioside were performed, giving five different amides, the methyl ester, and the primary alcohol. The products were purified, and their structures were investigated by negative FAB mass spectrometry. Binding of E. coli K99 was tested by incubating 35S-labeled bacteria with derivatized compounds separated on thin-layer chromatograms. Modification of the carboxyl group to a primary amide strengthened the binding at least 5-fold, as estimated from autoradiography of dilutions on thin-layer plates. Some strengthening of the binding was also obtained with the methylamide as well as with the carboxyl group reduced to the alcohol. The ethylamide bound equally well as the underivatized NeuGc-GM3. Amide substituents as large as propyl amide and benzyl amide were still recognized by the bacteria, although they bound weaker. The methyl ester was not stable in the chromatogram-binding assay with silica gel and water present, and it reverted to the acid.