Anthrax toxin complexes: heptameric protective antigen can bind lethal factor and edema factor simultaneously.
The 83 kDa protective antigen (PA(83)) component of anthrax toxin, after proteolytic activation, self-associates to form ring-shaped heptamers ([PA(63)](7)) that bind and aid delivery of the Edema Factor (EF) and Lethal Factor (LF) components to the cytosol. Here we show using fluorescence (Förster) resonance energy transfer that a molecule of [PA(63)](7) can bind EF and LF simultaneously. We labeled EF and LF with an appropriate donor/acceptor pair and found quenching of the donor and an increase in sensitized emission of the acceptor when, and only when, a mixture of the labeled proteins was combined with [PA(63)](7). Addition of unlabeled PA(63)-binding domain of LF to the mixture competitively displaced labeled EF and LF, causing a loss of energy transfer. In view of the known maximum occupancy of 3 ligand molecules per [PA(63)](7), these findings indicate that PA, EF, and LF can form mixtures of liganded toxin complexes containing both EF and LF.
Pimental
Ruth-Anne L
RA
Department of Microbiology and Molecular Genetics, Harvard Medical School, Boston, MA 02115, USA.
Christensen
Kenneth A
KA
Krantz
Bryan A
BA
Collier
R John
RJ
D000942:Antigens, Bacterial / Q000737:chemistry*; D001427:Bacterial Toxins / Q000737:chemistry*; D001665:Binding Sites; D045424:Complex Mixtures / Q000737:chemistry*; D031541:Fluorescence Resonance Energy Transfer; D046911:Macromolecular Substances; D011485:Protein Binding; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D021122:Protein Subunits / Q000737:chemistry
D000942:Antigens, Bacterial; D001427:Bacterial Toxins; D045424:Complex Mixtures; D046911:Macromolecular Substances; D021122:Protein Subunits; C030325:anthrax toxin