EBULIN-1, A NONTOXIC NOVEL TYPE-2 RIBOSOME-INACTIVATING PROTEIN FROM SAMBUCUS-EBULUS L LEAVES

A novel type 2 ribosome-inactivating protein (RIP) that we named ebuli n 1 has been isolated from leaves of Sambucus ebulus L. (Caprifoliacea e). In vitro ebulin 1 strongly inhibited protein synthesis by rabbit r eticulocyte lysates, rat brain, and rat liver cell-free systems but di d not affect in vitro plant nor bacterial protein synthesis. Ebulin 1 is composed of two subunits, a catalytic A subunit (M(r) 26,000) and a D-galactose-binding lectin B subunit (M(r) 30,000). Amino-terminal am ino acid sequence homology revealed the novelty that the ebulin 1 A-ch ain shares a high degree of homology not with the A-chain of other typ e 2 RIPs but rather with the Cucurbitaceae type 1 RIP briodin S and th e anti-human immunodeficiency virus type I proteins trichosanthin and TAP 29. Upon treatment with acid aniline the rRNA from ebulin 1-treate d rabbit reticulocyte ribosomes released the RNA fragment which is dia gnostic of RIP catalytic action. Ebulin 1 was nontoxic to mice up to 2 mg/kg of body weight and did not inhibit protein synthesis in culture d NHC human epithelial cells which are highly sensitive to ricin.