Probing of the Combining Site of the PapG Adhesin of Uropathogenic Escherichia coli Bacteria by Synthetic Analogues of Galabiose

The binding between uropathogenic Escherichia coli bacteria and human P erythrocytes was investigated by use of the hemagglutination inhibitors methyl 4-O-α-D-galactopyranosyl-β-D-galactopyranoside (methyl β-D-galabioside, 1), the monodeoxy (2,3,7,10,11,13,16), some O-methyl (6,9,12), deoxyfluoro (8,14,17), C-methyl (4), and C-ethyl (5) derivatives and various glycosides (18–26). The β-galabiose portion of the glycolipids present on P erythrocytes was found to bind to the pilus-located adhesin of the bacteria by hydrogen bonds directed toward five oxygen atoms situated on an edge of the disaccharide and by interactions between nonpolar surfaces in the sugar and the protein. One of the two remaining hydroxyl groups of galabiose seems to be in contact with a nonpolar cavity of the adhesin and the other with the surrounding aqueous medium.