Isolation and characterization of Viscumin a toxic lectin from VISCUM ALBUM L.

Journal/Book: J. Biol. Chem. 257 (22), 13263-13270. 1982;

Abstract: A toxic protein, viscumin, was isolated from extracts of mistletoe byaffinity chromatography on acid-treated Sepharose 4B. Viscumin wasselectively bound to the column and could be eluted with lactose. Itmigrated in polyacrylamide gel electrophoresis in the presence of sodiumdodecyl sulfate corresponding to Mr = 60,000. In addition, two bandsmigrating corresponding to Mr = 29,000 and 32,000 were found. Aftertreatment with 2-mercaptoethanol, only 2 bands (Mr = 29,000 and 34,000)were found. Apparently, viscumin consists of two chains which, in someof the molecules, are disulfide-linked. Protection experiments withantiserum against viscumin indicated that the major part of thecytotoxic activity in mistletoe extracts is due to viscumin. Gelfiltration experiments on Sephacryl 200 indicated that, at lowconcentrations, viscumin occurs as a monomer and at higherconcentrations as a dimer. Viscumin was found to inhibit proteinsynthesis in cell-free systems. When the two constituent peptide chainsof viscumin were eluted from polyacrylamide gels and tested for abilityto inhibit cell-free protein synthesis, this property was found to beassociated with the fastest migrating chain, here denoted the A chain.The heavier chain was denoted the B chain. The A chain was found toinhibit protein synthesis by inactivating the ribosomes catalytically.Reconstitution experiments with isolated ribosomal subunits fromuntreated and A chain-treated ribosomes showed that the 60 S ribosomalsubunit was selectively inactivated. Author.

Keyword(s): ANIMAL

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