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Semin Cell Biol. 1991 Feb;2(1):23-30.

The structure and action of ricin, a cytotoxic N-glycosidase.

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  • 1Clayton Foundation Biochemical Institute, Department of Chemistry and Biochemistry, University of Texas, Austin 78712.


The X-ray structure of the heterodimeric plant cytotoxin ricin has been elucidated. The A chain, known to be a specific N-glycosidase, has a prominent active site cleft. The B chain is a two domain lectin, which arose from the replication of a primitive sugar binding peptide. The molecular model reveals residues which are likely to be important in the action of the protein. Site directed mutagenesis reveals the relative importance of a number of these groups. A model for the mechanism of the A chain, including steric strain of the scissile bond and carboxonium ion transition state stabilization is proposed.

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