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.