Bryodin 2 A ribosome-inactivating protein isolated from the plant bryonia dioica

The present invention discloses a new ribosome-inactivating protein, bryodin 2, isolated from the plant Bryonia dioica. This ribosome-inactivating protein (RIP) is a type IRIP having a single polypeptide chain and no cellular receptor domain. Like many type I RIPs, bryodin 2 has a molecular weight of about 27,000 daltons and a pI of 9.5. Bryodin 2 differs from previously identified ribosome-inactivating protein in its amino acid composition, amino acid sequence, and toxicity in vitro and in vivo. Bryodin 2 is useful, as are other type I ribosome-inactivating proteins, as an abortifacient, immunomodulator, anti-tumor or anti-viral agent. Compositions comprising bryodin 2 as an immunoconjugate or fusion molecule are particularly useful to kill cells of a target population.