Transferrin associated with the porcine intestinal mucosa is a receptor specific for K88ab fimbriae of Escherichia coli.

Putative receptors of Escherichia coli K88 fimbriae are either tightly membrane bound or an integral part of membranes. Thus, proteins associated with piglet small intestinal mucosae were solubilized by a detergent (deoxycholate). A 74-kDa glycoprotein (GP74) purified from enterocyte and brush border membrane preparations was specifically detected in vitro by K88ab fimbriae. GP74 was recognized only in the mucosae of phenotypically adhesive animals. Metaperiodate treatment abolished the recognition, indicating that K88ab fimbriae-GP74 binding required the carbohydrate moiety. This glycoprotein belongs to the transferrin family and differed from the serum transferrin of the same adhesive-phenotype piglets. Unlike intestinal transferrin, serum transferrin was recognized independently of the adhesion phenotype. The glycan moieties of intestinal and serum transferrins differed in their molar compositions. Transferrin GP74 contained one monosialylated and monofucosylated glycan chain of the N-acetyllactosamine type. Intestinal holotransferrin exhibited pI values of 5.2, 5.3, 5.5, and 5.6, whereas serum holotransferrin pI values ranged between 5.4 and 6.2. Since mucosal transferrin was found intimately entrapped on membranes, we hypothesize that a K88ab fimbriae-transferrin-cell transferrin receptor complex might allow the bacteria to adhere to specific sites of the mucosa.