Site-Specific Labeling and ¹⁹F NMR Provide Direct Evidence for Dynamic Behavior of the Anthrax Toxin Pore ϕ-Clamp Structure
2021
Gonti, Srinivas | Westler, William M. | Miyagi, Masaru | Bann, James G.
The anthrax toxin protective antigen (PA), the membrane binding and pore-forming component of the anthrax toxin, was studied using ¹⁹F NMR. We site-specifically labeled PA with p-fluorophenylalanine (pF-Phe) at Phe427, a critically important residue that comprises the ϕ-clamp that is required for translocation of edema factor (EF) and lethal factor (LF) into the host cell cytosol. We utilized ¹⁹F NMR to follow low-pH-induced structural changes in the prepore, alone and bound to the N-terminal PA binding domain of LF, LFN. Our studies indicate that pF-Phe427 is dynamic in the prepore state and then becomes more dynamic in the transition to the pore. An increase in dynamic behavior at the ϕ-clamp may provide the necessary room for movement needed in translocating EF and LF into the cell cytosol.
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