Multivalent binding of ricin to bovine serum albumin-based neoglycoconjugates

Ricin, a ribosome-inactivating protein from the plant Ricinus communis, is a heterodimeric protein. The A chain is a N-glycosidase and the B chain (RTB) is a lectin with two carbohydrate binding sites. RTB has been shown to bind asialofetuin with much greater affinity than it does galactose, supporting the hypothesis that it may exhibit multivalency. To test this, neoglycoconjugates were prepared and tested for their ability to function as ligands for ricin binding. Because the two carbohydrate binding sites on RTB are approximately 70A apart, bovine serum albumin (BSA) was used as the carbohydrate carrier. It was derivatized with either the oligosaccharide portion of asialo-GM1 or with lactose. These sugars were used because ricin was found to adhere more effectively to asialo-GM1 and LacCer immobilized on plastic than to the other glycosphingolipids tested. Results of binding studies done using surface plasmon resonance indicated that the RTB subunit of ricin exhibited a multivalent effect when it bound to the neoglycoconjugates.