Abstract
A cyanogen bromide fragment derived from the K88ab adhesin inhibited the hemagglutinating activity of K88 fibrillae. Smaller fragments which inhibited the adherence of K88 fibrillae to erythrocytes or to intestinal epithelial cells were obtained by digestion of K88ab fibrillae with alpha-chymotrypsin. Active peptides were isolated from the digestion mixture and identified as Ser-Leu-Phe and Ala-Ile-Phe. Both tripeptides correspond to the peptide stretches Ser-148-Leu-Phe-150 and Ala-156-Ile-Phe-158, respectively, which are part of conserved regions in the primary structure of the K88 variants ab, ac, and ad. The isolated tripeptides inhibited the hemagglutinating activity of purified K88 fibrillae in the 1 to 5 microM range, while adherence of the fibrillae to intestinal epithelial cell brush borders was inhibited in the 10 to 50 microM range. Furthermore, the tripeptides were capable of eluting attached bacteria from agglutinated erythrocytes. The inhibitory activity of the isolated peptides was confirmed by testing various synthetic peptides for their ability to inhibit the interaction of the different K88 variants with various species of erythrocytes. The significance of these findings for the localization of the receptor-binding domain is discussed.