Elderberry (Sambucus Nigra) Bark Contains two Structurally Different Neusac(α2,6)Gal/Galnac-Binding Type 2 Ribosome-Inactivating Proteins

A second NeuAc(a2,6)Gal/GalNAc binding type 2 ribosome-inactivating protein (RIP), called SNAI’ has been isolated from elderberry (Sumbucus nigru) bark. SNAI’ is a minor bark protein which closely resembles the previously described major Neu5Ac(a2,6)Gal/GalNAc binding type 2 RIP called SNAI with respect to its carbohydrate-binding specificity and ribosome-inactivating activity but has a different molecular structure. Molecular cloning revealed that the deduced amino acid sequence of SNAI’ is highly similar to that of SNAI and that the difference in molecular structure between both proteins relies on a single cysteine residue present in the B chain of SNAI but absent from SNAI’. The isolation of SNAI’ not only identifies a minor bark protein as a type 2 RIP but also further emphasizes the complexity of the type 2 RIP/lectin mixture present in the bark of elderberry.