CHARACTERIZATION OF THE CARBOHYDRATE MOIETY OF INTESTINAL MUCIN-TYPE SIALOGLYCOPROTEIN RECEPTORS FOR THE K88AC FIMBRIAL ADHESIN OF ESCHERICHIA-COLI

We have previously identified two mucin-type sialoglycoproteins from p orcine intestinal epithelial cells with approximate molecular masses o f 210 (intestinal mucin-type glycoprotein IMTGP-1) and 240 kDa (IMTGP- 2) as receptors for the K88ab and K88ac fimbrial adhesins of Escherich ia coli. These receptors are detected in intestinal brush border membr ane preparations from pigs with adhesive phenotypes but not from pigs with nonadhesive phenotypes and are postulated to be important determi nants of the susceptibility of pigs to K88ab(+) and K88ac(+) enterotox igenic E. coli infections. Using exoglycosidase digestion studies, we have now determined that beta-linked galactose is an important compone nt in the recognition of IMTGP-1 and IMTGP-2 by the K88ac adhesin. In addition, we observed a differential distribution of the K88ac adhesin binding activity of IMTGP-1 and IMTGP-2 along the crypt-villus axis, suggesting that receptor activity is dependent on the maturation state of the intestinal epithelial cells. Brush borders from immature intes tinal epithelial cells possessed the highest concentrations of IMTGP-1 and IMTGP-2 receptor activity, with a progressive decrease in recepto r activity as the cells mature. To characterize the differences in the carbohydrate moieties of IMTGP-1 and IMTGP-2, we developed a procedur e for purifying the receptors, using phenol extraction followed by ser ial lectin affinity chromatography. Carbohydrate compositional analysi s of the purified receptors indicated that the carbohydrate moieties o f IMTGP-1 and IMTGP-2 consist of both N- and O-glycans containing gala ctose, glucose, sialic acid, mannose, N-acetylgalactosamine, N-acetylg lucosamine, and fucose. The major difference between the two receptors is that IMTGP-2 contains a higher percentage of monosaccharides (mann ose and glucose) commonly found in N-glycans.