The structure and action of ricin, a cytotoxic N-glycosidase.
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.
Robertus
J
J
Clayton Foundation Biochemical Institute, Department of Chemistry and Biochemistry, University of Texas, Austin 78712.
D000595:Amino Acid Sequence; D003461:Crystallography; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D011487:Protein Conformation; D012276:Ricin / Q000737:chemistry* / Q000235:genetics; D013329:Structure-Activity Relationship
D012276:Ricin