Laboratory for Phytopathology and Plant Protection, Katholieke Universiteit Leuven, Belgium; 2Institut de Pharmacologie et Biologie Structurale, UMR-CNRS 5089, Toulouse Cedex, France; 3Rega Institute, Laboratory of Molecular Immunology, Katholieke Universiteit Leuven, Belgium Fruits of elderberry (Sambucus nigra) express small quantities of a type-2 ribosome-inactivating protein with an exclusive specificity towards the NeuAc(a2,6)Gal/GalNAc disaccharide and a unique molecular structure typified by the occurrence of a disulfide bridge between the B-chains of two adjacent protomers