Identification of cholera toxin binding glycoproteins in rat intestinal microvillus membranes

Glycoproteins of the microvillus membranes from rat small intestinal epithelial cells were examined for their ability to bind cholera toxin. Membrane glycoproteins prepared by Ricinus communis agglutinin-Sepharose affinity chromatography, which were free of glycolipids, were shown to be able to form complexes with iodinated cholera toxin by gel filtration column chromatography. These glycoproteins were further characterized by subjecting the complex of tritiated cholera toxin receptors, cholera toxin, and anti-cholera toxin antibody to sodium dodecyl sulfate-polyacrylamide gel electrophoresis and fluorography and by localizing cholera toxin binding glycoproteins on sodium dodecyl sulfate-gels using iodinated cholera toxin. In addition to glycolipids, at least 5 glycoproteins with molecular weights of 69,000, 90,000, 100,000, 114,000, and 132,000 were identified by both methods. These results suggest that microvillus membranes contain glycoprotein and glycolipid receptors for cholera toxin.