title: Mutational analysis of the Shiga toxin and Shiga-like toxin II enzymatic subunits.
abstract: The A-subunit polypeptides of Shiga toxin, the Shiga-like toxins (SLTs), and the plant lectin ricin inactivate eucaryotic ribosomes by enzymatically depurinating 28S rRNA. Comparison of the amino acid sequences of the members of the Shiga toxin family and ricin revealed two regions of significant homology that lie within a proposed active-site cleft of the ricin A chain. In previous studies, these conserved sequences of the SLT-I and ricin A subunits have been implicated as active sites. To establish the importance of these regions of homology, we used site-directed mutagenesis to alter the A-subunit sequences of two members of the Shiga toxin family. Substitution of an aspartic acid for glutamic acid 166 of the Slt-IIA subunit decreased the capacity of the polypeptides to inhibit protein synthesis at least 100-fold in a cell-free translation system. However, this mutation did not prevent the expression of immunoreactive, full-length Slt-IIA. In addition, SLT-II holotoxin containing the mutated A subunit was 1,000-fold less toxic to Vero cells. Finally, site-directed mutagenesis was used to delete sequences encoding amino acids 202 through 213 of the Shiga toxin A subunit. Although this deletion did not prevent holotoxin assembly, it abolished cytotoxic activity.
authors.affiliation: Department of Microbiology, Uniformed Services University of the Health Sciences, Bethesda, Maryland 20814.
authors.forename: M P
authors.initials: MP
authors.lastname: Jackson
authors.forename: R L
authors.initials: RL
authors.lastname: Deresiewicz
authors.forename: S B
authors.initials: SB
authors.lastname: Calderwood
mesh_terms: D000595:Amino Acid Sequence; D001427:Bacterial Toxins / Q000032:analysis*; D001665:Binding Sites; D004768:Enterotoxins / Q000032:analysis*; D009154:Mutation; D022641:Shiga Toxin 2; D022603:Shiga Toxins
chemical_list: D001427:Bacterial Toxins; D004768:Enterotoxins; D022641:Shiga Toxin 2; D022603:Shiga Toxins