Plasmid-bearing (but not plasmid-cured) Yersinia enterocolitica is known to bind to purified small intestinal mucins from rabbits and humans. This study examined which region(s) of the mucin molecule is important for bacterial adherence. Pronase digestion of mucin and removal of nonglycosylated or poorly glycosylated peptide regions had no effect on bacterial binding, suggesting that plasmid-bearing Y. enterocolitica interacts with mucin carbohydrate. Periodate oxidation also did not alter bacterial adherence, indicating that vicinal hydroxyl groups in the mucin sugars are not important for binding. Boiling of mucin, depolymerization by reduction of disulfide bonds, or removal of noncovalently associated lipid actually enhanced bacterial adherence, suggesting that plasmid-bearing Y. enterocolitica can interact with additional domains in the mucin molecule revealed by these treatments. These domains were destroyed by pronase digestion. In delipidated mucin (but not in reduced or boiled mucin), binding to these domains appeared to be hydrophobic since it could be prevented by treatment of bacteria with tetramethyl urea. Oligosaccharides obtained from both human and rabbit small intestinal mucins were capable of inhibiting attachment of plasmid-bearing (but not plasmid-cured) Y. enterocolitica to mucin. After removal of terminal and backbone sugar residues by treatment of mucin with trifluoromethanesulfonic acid, binding of plasmid-bearing bacteria increased significantly when N-acetylgalactosamine, either alone or with galactose attached, was revealed, indicating that core regions of the sugar side chains are involved in bacterial binding. Adherence of plasmid-cured organisms was unaffected by trifluoromethanesulfonic acid treatment of mucin. We concluded that virulent Y. enterocolitica interacts with the carbohydrate moiety of native small intestinal mucin through a plasmid-mediated process. When mucin becomes denatured, binding of the organism can increase through hydrophobic and nonhydrophobic interactions with (most likely) the mucin protein
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