title: Conformation-dependent antigenic determinants in the toxic lectin ricin.
abstract: The major part of the ricin-precipitable antibodies in sera produced by immunizing rabbits with formaldehyde-treated ricin is precipitated also by the isolated ricin A and B chains. In contrast, in antisera produced by immunizing with formaldehyde-treated ricinus agglutinin only a small part of the antibodies cross-reacting with ricin can be precipitated by the isolated A and B chains, or bound to immunoabsorbents containing the isolated ricin chains. In immunodiffusion studies with anti-ricinus agglutinin sera, a star-shaped precipitate was formed when isolated A and B chains recombined to form intact ricin. Both anti-ricin and anti-ricinus agglutinin sera neutralized effectively the ability of ricin to inhibit protein synthesis in HeLa cells. Anti-ricin serum also neutralized the inhibitory effect of the isolated A chain on protein synthesis in a cell-free system and the ability of the isolated B chain to induce indirect hemagglutination. In contrast, antiricinus agglutinin serum did not neutralize the biologic activities of the isolated ricin A and B chains. Anti-ricinus agglutinin serum formed a precipitate with the hybrid ricin A chain/abrin B chain, and protected against the toxic effect on HeLa cells of this hybrid, indicating conformational changes of ricin A chain upon binding to the B chain. It is concluded that the anti-ricinus agglutinin serum contains antibodies directed against conformational determinants present on intact ricin, but not present or exposed in the isolated A and B chains. At least part of these conformational determinants appears to be carried by the A chain.
mesh_terms: D000906:Antibodies / Q000302:isolation & purification; D002250:Carbon Radioisotopes; D002474:Cell-Free System; D002846:Chromatography, Affinity; D000939:Epitopes; D006367:HeLa Cells; D006386:Hemagglutination Tests; D005779:Immunodiffusion; D007930:Leucine / Q000378:metabolism; D010940:Plant Proteins / Q000276:immunology*; D011487:Protein Conformation; D012276:Ricin / Q000276:immunology*
chemical_list: D000906:Antibodies; D002250:Carbon Radioisotopes; D000939:Epitopes; D010940:Plant Proteins; D012276:Ricin; D007930:Leucine