Isolation and characterization of four type 2 ribosome inactivating pulchellin isoforms from Abrus pulchellus seeds

• Published in: The FEBS journal 2008-03, Vol.275 (5), p.948-959
• Main Authors: Castilho, Priscila V, Goto, Leandro S, Roberts, Lynne M, Araújo, Ana Paula U
• Format: Article
• Language: English
• Subjects: Abrus - chemistry; Abrus pulchellus; Amino Acid Sequence; Binding sites; Biochemistry; Botany; Carbohydrates - chemistry; characterization; cloning; HeLa Cells; Hemagglutination - drug effects; Hemagglutination Inhibition Tests; Humans; Inhibitory Concentration 50; isoforms; Molecular Sequence Data; Protein Isoforms - chemistry; Protein Isoforms - isolation & purification; Protein Isoforms - toxicity; Protein Structure, Secondary; Ribosome Inactivating Proteins, Type 2 - chemistry; Ribosome Inactivating Proteins, Type 2 - isolation & purification; Ribosome Inactivating Proteins, Type 2 - toxicity; ribosome‐inactivating protein; Seeds; Seeds - chemistry; Sequence Alignment; Sugar; Toxicology
• ISSN: 1742-464X; 1742-4658
• DOI: 10.1111/j.1742-4658.2008.06258.x

Abrus pulchellus seeds contain at least seven closely related and highly toxic type 2 ribosome-inactivating pulchellins, each consisting of a toxic A-chain linked to a sugar binding B-chain. In the present study, four pulchellin isoforms (termed P I, P II, P III and P IV) were isolated by affinity, ion exchange and chromatofocusing chromatographies, and investigated with respect to toxicity and sugar binding specificity. Half maximal inhibitory concentration and median lethal dose values indicate that P I and P II have similar toxicities and that both are more toxic to cultured HeLa cells and mice than P III and P IV. Interestingly, the secondary structural characteristics and sugar binding properties of the respective pairs of isoforms correlate well with the two toxicity levels, in that P I/P II and P III/P IV form two specific subgroups. From the deduced amino acids sequences of the four isoforms, it is clear that the highest similarity within each subgroup is found to occur within domain 2 of the B-chains, suggesting that the disparity in toxicity levels might be attributed to subtle differences in B-chain-mediated cell surface interactions that precede and determine toxin uptake pathways.