Purification and Conjugation of Type 1 Ribosome-Inactivating Proteins

Ribosome-inactivating proteins (RIPs, 1 ) are plant enzymes that damage ribosomes in an irreversible manner. They can be divided into type 1 RIPs, which are single-chain proteins, and type 2 RIPs, which are heterodimeric proteins consisting of an enzymatically active A-chain connected by a disulfide bond to a B-chain. The latter has the properties of a lectin specific for sugars with the galactose conformation and binds to galactosyl-terminated receptors on the cell surface, thus allowing the A-chain to enter the cytoplasm. Consequently, most type 2 RIPs are potent toxins, the best known being ricin, while type 1 RIPs are much less toxic.