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., and Karlsson, K.-A. (1990) FEBS Lett. 263, 10-14] f or the enterotoxigenic bacteria Escherichia coli K99 is the gangliosid e NeuGc-GM3 (NeuGc alpha 3Gal beta 4Glc beta Cer) [e.g., H. Smit, W. G aastra, J. P. Kamerling, J. F. G. Vliegenthart, and F. K. de Graaf (19 84) Infect. Immun. 46, 578-584]. Chemical modifications of the carboxy l group of this ganglioside were performed, giving five different amid es, the methyl ester, and the primary alcohol. The products were purif ied, and their structures were investigated by negative FAB mass spect rometry. Binding of E. coli K99 was tested by incubating S-35-labeled bacteria with derivatized compounds separated on thin-layer chromatogr ams. Modification of the carboxyl group to a primary amide strengthene d the binding at least 5-fold, as estimated from autoradiography of di lutions on thin-layer plates. Some strengthening of the binding was al so obtained with the methylamide as well as with the carboxyl group re duced to the alcohol. The ethylamide bound equally well as the underiv atized NeuGc-GM3. Amide substituents as large as propyl amide and benz yl amide were still recognized by the bacteria, although they bound we aker. The methyl ester was not stable in the chromatogram-binding assa y with silica gel and water present, and it reverted to the acid.