title: Volkensin from Adenia volkensii Harms (kilyambiti plant), a type 2 ribosome-inactivating protein.
abstract: Volkensin, a type 2 ribosome-inactivating protein from the roots of Adenia volkensii Harms (kilyambiti plant) was characterized both at the protein and nucleotide level by direct amino acid sequencing and cloning of the gene encoding the protein. Gene sequence analysis revealed that volkensin is encoded by a 1569-bp ORF (523 amino acid residues) without introns, with an internal linker sequence of 45 bp. Differences in residues present at several sequence positions (reproduced after repeated protein sequence analyses), with respect to the gene sequence, suggest several isoforms for the volkensin A-chain. Based on the crystallographic coordinates of ricin, which shares a high sequence identity with volkensin, a molecular model of volkensin was obtained. The 3D model suggests that the amino acid residues of the active site of the ricin A-chain are conserved at identical spatial positions, including Ser203, a novel amino acid residue found to be conserved in all known ribosome-inactivating proteins. The sugar binding site 1 of the ricin B-chain is also conserved in the volkensin B-chain, whilst in binding site 2, His246 replaces Tyr248. Native volkensin contains two free cysteinyl residues out of 14 derived from the gene sequence, thus suggesting a further disulphide bridge in the B chain, in addition to the inter- and intrachain disulphide bond pattern common to other type 2 ribosome-inactivating proteins.
authors.affiliation: Dipartimento di Scienze della Vita, Seconda Università di Napoli, Caserta, Italy.
authors.forename: Angela
authors.initials: A
authors.lastname: Chambery
authors.forename: Antimo
authors.initials: A
authors.lastname: Di Maro
authors.forename: Maurilia M
authors.initials: MM
authors.lastname: Monti
authors.forename: Fiorenzo
authors.initials: F
authors.lastname: Stirpe
authors.forename: Augusto
authors.initials: A
authors.lastname: Parente
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D001665:Binding Sites; D003001:Cloning, Molecular; D017931:DNA Primers; D018744:DNA, Plant / Q000235:genetics / Q000302:isolation & purification; D006023:Glycoproteins / Q000737:chemistry / Q000235:genetics* / Q000302:isolation & purification; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009699:N-Glycosyl Hydrolases / Q000235:genetics* / Q000302:isolation & purification; D010446:Peptide Fragments / Q000737:chemistry; D018515:Plant Leaves / Q000235:genetics; D037121:Plant Lectins / Q000737:chemistry / Q000235:genetics* / Q000302:isolation & purification; D011487:Protein Conformation; D021122:Protein Subunits / Q000737:chemistry / Q000235:genetics; D011994:Recombinant Proteins / Q000737:chemistry; D054790:Ribosome Inactivating Proteins, Type 2; D027824:Rosaceae / Q000235:genetics*; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid
chemical_list: D017931:DNA Primers; D018744:DNA, Plant; D006023:Glycoproteins; D010446:Peptide Fragments; D037121:Plant Lectins; D021122:Protein Subunits; D011994:Recombinant Proteins; D054790:Ribosome Inactivating Proteins, Type 2; C049134:volkensin; D009699:N-Glycosyl Hydrolases