Protective antigen constitutes one of the three proteins composing the anthrax toxin; it mediates attachment to host cells and translocation of edema factor (EF) and lethal factor (LF) into the host cytoplasm PA associated with LF forms the lethal toxin (LeTx) and causes death when injected; PA associated with EF forms the edema toxin (EdTx) and produces edema PA induces immunity to infection with anthrax ; [Protective antigen]: Mediates the attachment to host cells by binding host cell receptors ANTXR1 and ANTXR2 Following host cell surface attachment, PA is cleaved by FURIN to generate the PA-63 (Protective antigen PA-63) form, which constitutes the mature form of the protein that oligomerizes and forms a pore to translocate the enzymatic toxin components edema factor (EF) and lethal factor (LF) into the host cytosol ; [Protective antigen PA-63]: Mature form that oligomerizes and forms a pore to translocate the enzymatic toxin components edema factor (EF) and lethal factor (LF) into the host cytosol Following attachment to host cell receptors and cleavage by FURIN, homooligomerizes to form ring-shaped oligomers that are in a pre-pore conformation, and associates with EF and LF Toxin-leaded complexes are then endocytosed in a clathrin-dependent process, followed by a conformational change of oligomerized PA-63 from the pre-pore to pore state, which is triggered by the low pH in the endosome Once active, the pore mediates unfolding of EF and LF, which pass through the pore and translocate into the host cytosol

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