title: Presence of polymerized and free forms of the non-toxic type 2 ribosome-inactivating protein ebulin and a structurally related new homodimeric lectin in fruits of Sambucus ebulus L.
abstract: Mature leaves of dwarf elder (Sambucus ebulus L.) contain the non-toxic type 2 ribosome-inactivating protein ebulin 1 (Girbés et al., 1993b, J. Biol. Chem. 268: 18195-18199). We have now found that the green fruits of dwarf elder contain both free and polymerized forms of ebulin (ebulin f) and a new homodimeric D-galactose-binding lectin (SELfd). Polymerized material containing ebulin and lectin is composed of aggregates of variable relative molecular mass, some of them being close to 250,000. These aggregate forms are maintained in part by reducible disulphide bridges and reconstitute from reductant-free dialyzed material previously reduced with 2-mercaptoethanol. Direct incubation of free ebulin f with the free SELfd did not lead to polymerization, thus indicating that polymerization triggers some kind of substantial and perhaps catalyzed change in the structure of these proteins. Ebulin-containing polymerized material reacts with anti-ebulin f antibodies. Our results indicate that ebulin f is a fruit-form of ebulin 1. In contrast to green fruits, mature fruits lack both polymerized material and ebulin f, thus indicating some kind of reserve role for them in green fruits. Polymerization of ebulin and the dimeric lectin may represent a novel means of storing the non-toxic type 2 ribosome-inactivating proteins and lectins found in highly metabolic tissues, such as green fruits.
authors.affiliation: Departamento de Bioquímica y Biología Molecular, Facultad de Ciencias, Universidad de Valladolid, Spain.
authors.forename: L
authors.initials: L
authors.lastname: Citores
authors.forename: F M
authors.initials: FM
authors.lastname: de Benito
authors.forename: R
authors.initials: R
authors.lastname: Iglesias
authors.forename: J
authors.initials: J
authors.lastname: Miguel Ferreras
authors.forename: P
authors.initials: P
authors.lastname: Argüéso
authors.forename: P
authors.initials: P
authors.lastname: Jiménez
authors.forename: E
authors.initials: E
authors.lastname: Méndez
authors.forename: T
authors.initials: T
authors.lastname: Girbés
mesh_terms: D000595:Amino Acid Sequence; D001704:Biopolymers; D003429:Cross Reactions; D005690:Galactose / Q000378:metabolism; D008969:Molecular Sequence Data; D010940:Plant Proteins / Q000737:chemistry* / Q000378:metabolism / Q000494:pharmacology; D011485:Protein Binding; D014176:Protein Biosynthesis / Q000187:drug effects; D054790:Ribosome Inactivating Proteins, Type 2; D017386:Sequence Homology, Amino Acid; D014197:Trees / Q000737:chemistry*
chemical_list: D001704:Biopolymers; D010940:Plant Proteins; D054790:Ribosome Inactivating Proteins, Type 2; C107391:ebulin r protein, Sambucus ebulus; D005690:Galactose