Escherichia coli strain RDEC-1 AF/R1 endogenous fimbrial glycoconjugate receptor molecules in rabbit small intestine

Escherichia coli strain RDEC-1 causes a diarrheagenic infection in rabbits with AF/R1 fimbriae, which have been identified as an important colonizatio n factor in RDEC-1 adherence leading to disease, The AF/R1-mediated RDEC-1 adherence model has been used as a model systems for E, coli diarrheal dise ases. In this study, RDEC-1 adhered specifically to small intestinal brush borders, with both sialic acid and beta -galactosyl residues apparently inv olved, The AF/R1-mediated adherence activity of [C-14]-labeled RDEC-1 was a nalyzed quantitatively by using 24-well plates coated with purified brush b orders and purified microvilli, Two microvillus membrane proteins (130 and 140 kDa) were individually isolated, and chicken antibody raised to each pr otein inhibited bacterial adherence, These same two proteins, previously sh own to be recognized by AF/R1, were individually digested with trypsin, and the amino acid sequences of peptides were determined by reversed-phase cap illary liquid chromatography-mass spectrometry tandem mass spectrometry (LC -MS). This LC-MS analysis indicated that these proteins are subunits of the rabbit sucrase-isomaltase protein (SI) complex Guinea pig serum raised to purified rabbit SI complex inhibited bacterial adherence to microvilli. Add itionally, as determined by high-performance thin-layer chromatography and autoradiography, RDEC-1 adhered selectively, via AF/R1 fimbriae, to a glyco lipid tentatively identified as galactosylceramide (Gal beta1-1Cer) in the lipid extract of rabbit small intestinal brush borders. RDEC-1 adherence to Gal beta1-1Cer was partially inhibited in the presence of galactose, These combined results indicate that the endogenous receptor molecule for AF/R1 fimbriae of RDEC-1 is each individual component of the SI complex, although binding to glycolipid may be responsible for an additional adherence mecha nism.