Stoichiometry of anthrax toxin complexes.

摘要: After being proteolytically activated, the protective antigen (PA) moiety of anthrax toxin self-associates to form symmetric, ring-shaped heptamers. Heptameric PA competitively binds enzymatic moieties toxin, edema factor and lethal factor, translocates them across endosomal membrane by a pH-dependent process. We used two independent approaches determine how many seven identical EF/LF binding sites heptamer can be occupied simultaneously. measured isotope ratios in complexes assembled from differentially radiolabeled subunits, we determined molecular masses unlabeled multiangle laser light scattering. Both yielded same value: solution three molecules protein ligand under saturating conditions. This suggests that each bound sterically occludes subunits. According this model, ligand-saturated is asymmetric, with six subunits occluded. These results contribute conceptual framework for understanding mechanism translocation toxin.