Anthrax bacteria ( ) produces Protective antigen toxin (PA), Lethal factor (LF) and Edema factor (EF) protein components into the host cells. Protective antigen toxin (PA83 - 83kDa polypeptide) binds to cell surface receptors. PA is cleaved into a 20kDa fragment and 63kDa fragment by Furin like protease. The is released, resulting in spontaneous oligomerization into heptamer that facilitates EF and LF to bind. The complex is endocytosed and acidic conditions in endosome triggers conformational changes in prepore complex and leading to a membrane spanning pore formation. Formation of pore allows translocation of LF and EF components into the cell. In pore structure "O"-ring shaped narrow 6 Å diameter ring Φ-clamp is formed by seven phenylalanine residues (Phe427). The Φ-clamp is not wide enough to allow protein secondary structure elements, it may allow only fully unfolded polypeptides to pass through PA pore. To use NMR as a tool, PA83 is labelled site specifically with -Fluoro-Phenyalalanine at Phe427 residue. Site specifically introduced probe helps to follow conformational changes and dynamic behavior of the Φ-clamp in prepore, bound prepore and pore state. Our results indicate that F-Phe427 is dynamic in the prepore state and then becomes more dynamic in the transition to the pore state. Further increase in dynamic behavior at the Φ-clamp in pore state may provide the necessary room for movement needed in translocating EF and LF into the cell cytosol.