Protective antigen protein of Bacillus anthracis (PA)

The **protective antigen protein of Bacillus anthracis** is the cell-binding and pore-forming component of anthrax toxin, which is a major virulence factor of *B. anthracis*, the causative agent of anthrax[1][2][4][6][8]. PA is an 83 kDa protein that binds to anthrax toxin receptors (ANTXR1/TEM8, ANTXR2/CMG2) on host cells and, after proteolytic cleavage, oligomerizes to form a prepore and then a membrane-spanning β-barrel pore. This pore enables the translocation of the other toxin components, lethal factor and edema factor, into the cytosol, disrupting cellular signaling and immune responses and ultimately contributing to the pathology of anthrax infection[1][2][3][4][6][7]. The protein is the main target of current anthrax vaccines and therapeutic monoclonal antibodies because neutralizing PA blocks toxin entry into cells and prevents disease[3][4][6]. Structurally, PA consists of four domains with distinct roles in receptor binding, oligomerization, and membrane insertion[1][3][5]. PA alone is not cytotoxic but is essential for the toxic action of the whole anthrax toxin complex[7].

Other names

Protective antigenAnthrax protective antigenPA83 (referring to full-length 83 kDa form)PA63 (cleaved 63 kDa active form)pagA (gene name)

Antibodies bind PA and block its attachment to host cells or its oligomerization, neutralizing anthrax toxin function Vaccines induce immune response (antibody production) to PA, preventing anthrax