CHARACTERIZATION OF A NEW NONTOXIC 2-CHAIN RIBOSOME-INACTIVATING PROTEIN AND A STRUCTURALLY-RELATED LECTIN FROM RHIZOMES OF DWARF-ELDER (SAMBUCUS-EBULUS L)

A new N-glycosidase ribosome-inactivating protein (RIP) belonging to t he novel family of the nontoxic type 2 RIPs from Sambucaceae has been isolated from rhizomes of dwarf elder (Sambucus ebulus L.) and named e bulin r. Dwarf elder rhizomes also contain a novel monomeric N-Ac-gala ctosamine-binding lectin that we named SEAII. Ebulin r and SEAII have two isoforms each one, which were readily resolved by ion exchange. Bo th isoforms of ebulin (ebulins r1 and r2) strongly inhibited protein s ynthesis in mammalian but not in plant ribosomes by promoting depurina tion of sensitive ribosomes. Ebulin r and SEAII have apparent molecula r masses of 56 and 33.5 kDa, respectively. Ebulins r1 and r2 are compo sed of two dissimilar subunits (types A-B) of apparent molecular masse s of 26 and 30 kDa linked by disulphide bridges. The rhizome SEAII and the lectins SNA II and SNA IU. from elder (Sambucus nigra L.) share g ood amino-acid sequence homology. The rhizome ebulin-A chain is more s equence-related to RIP members of cucurbitaceae than to any other plan t family. The rhizome ebulin B chain shares a large homology in aminoa cid sequence with ebulin 1-B chain and SEAII. Anti-ebulin 1 polyclonal antibodies raised in rabbits reacted better with ebulin r1 than with ebulin r2, thus suggesting that both RIP isoforms could have some diff erences.