Protective antigen protein (Bacillus anthracis) (PA)

Protective antigen is a protein secreted by *Bacillus anthracis* and is the cell-binding component of the anthrax toxin complex. It binds to anthrax toxin receptors on mammalian cells (such as ANTXR1 and ANTXR2), is proteolytically activated on the cell surface, oligomerizes to form a heptameric or octameric pre-pore, and facilitates the translocation of lethal factor and edema factor into the host cytosol by forming a transmembrane channel. PA is the immunodominant antigen in available anthrax vaccines and a key therapeutic target for neutralizing antibodies. The protein contains four domains, each mediating specific steps in receptor binding, oligomerization, membrane insertion, and enzymatic factor translocation. Blocking PA function abrogates anthrax toxin activity and prevents infection.

Other names

Protective antigenPAAnthrax protective antigenBacillus anthracis protective antigenPA83 (full-length)PA63 (activated form)PA20 (cleaved fragment)

Neutralizing monoclonal antibodies: bind PA and block its interaction with host cell receptors or prevent oligomerization and pore formation, thus preventing translocation of lethal factor and edema factor Vaccine-induced antibodies: stimulate immune system to produce neutralizing antibodies that block PA binding and function