title: Variation in chemical properties and antigenic determinants among type II heat-labile enterotoxins of Escherichia coli.
abstract: Type II heat-labile enterotoxin (LT-II) from Escherichia coli 41 was purified and compared with prototype LT-II encoded by genes from E. coli SA53. Both toxins were oligomeric proteins consisting of polypeptides A (Mr, 28,000) and B (Mr, 11,800). The A polypeptides were cleaved by trypsin into fragments A1 (Mr, 21,000) and A2 (Mr, about 7,000). These two toxins were shown to belong to two different subclasses of LT-II. We propose to designate the prototype toxin LT-IIa and the new variant LT-IIb. The pI of LT-IIb was between 5.2 and 5.6, significantly lower than the pI of 6.8 for LT-IIa, and the behavior of LT-IIb during purification differed significantly from that of LT-IIa. The toxic dose of unnicked LT-IIb in the Y1 adrenal-cell assay was 94 pg, but trypsin-treated, nicked LT-IIb was toxic at about 3 pg. In contrast, the toxic dose of LT-IIa was previously shown to be 0.5 to 1 pg for several preparations that varied from unnicked to partially nicked, and treatment with trypsin was not required for full toxicity. The titer of LT-II antiserum in neutralization tests was 100-fold greater against LT-IIa than against LT-IIb. In immunodiffusion tests, LT-IIa and LT-IIb gave a reaction of partial identity. In a radioimmunobinding assay, the titer of LT-IIa antiserum against homologous LT-IIa was approximately 10-fold greater than against LT-IIb. The cholera-E. coli family of heat-labile enterotoxins has been divided into serogroup I, which includes cholera toxin and the antigenic variants of E. coli heat-labile toxin designated LTh-I and LTp-I, and serogroup II, which includes LT-IIa and LT-IIb. The type I and type II toxins do not cross-react in neutralization or immunodiffusion tests. By using very sensitive radioimmunobinding assays, it was possible to demonstrate common antigenic determinants between the type I and type II toxins. However, the titers of antibodies in hyperimmune sera that recognized these common determinants were very low.
mesh_terms: D000936:Antigen-Antibody Complex; D001427:Bacterial Toxins / Q000235:genetics / Q000276:immunology / Q000302:isolation & purification*; D004768:Enterotoxins / Q000235:genetics / Q000276:immunology / Q000302:isolation & purification*; D000939:Epitopes / Q000032:analysis*; D004926:Escherichia coli / Q000235:genetics; D029968:Escherichia coli Proteins; D005796:Genes; D005798:Genes, Bacterial; D007106:Immune Sera; D008970:Molecular Weight
chemical_list: D000936:Antigen-Antibody Complex; D001427:Bacterial Toxins; D004768:Enterotoxins; D000939:Epitopes; D029968:Escherichia coli Proteins; D007106:Immune Sera; C027538:heat-labile enterotoxin, E coli