Anthrax toxin is composed of three proteins: protective antigen (PA), oedema factor, and lethal factor. PA binds to cell membranes to form a heptameric complex which forms a pore in the membrane. The pore then allows oedema and lethal factors to travel into the host cell, ultimately leading to cell death. The details of the PA interaction with membranes is not completely understood. In an effort to better understand how PA interacts with host cells, Langmuir monolayers were constructed at the air-water interface. Phospholipid monolayers are model cell membranes, and present as the exterior of a cell membrane when proteins are incorporated into the aqueous sub phase below the monolayer. Proteins including the wild form of PA (PA83), the heptameric form (PA63) and a PA 83 mutant were studied by measuring changes in surface pressure after placing proteins beneath the model membrane in separate studies. Protein penetration of phospholipid monolayers is indicated by increases in surface pressure over time. It was found that monomeric PA83 did not penetrate the films, and was crowded out of the surface with increasing lipid density. Heptameric PA63 penetrated the monolayers and caused significant increases in surface pressure through a range of lipid packing. The mutant PA83 was not expected to interact with the films and was tried as a negative control. Interestingly, this mutant did have positive interactions with the film at a pH of 5; a recently published structure indicates a nascent pore which may have limited interactions with membranes.

Interaction of anthrax toxin protective antigen protein with model cell membranes at the air-water interface

249th National Meeting (2015)

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