Anthrax Protective Antigen
Ansley Scott '02 and
Dawn Stancik '02
Recently anthrax has caused much concern as a
public health threat because of its use as a bioterrorism weapon.
However, anthrax has been a concern for farmers since biblical times, especially
in agricultural regions like South America and Africa. Although it
is rare, anthrax has been found sporadically in cattle, sheep, and goats
throughout the midwest and the western United States after injestion or
inhalation of the Bacillus anthracis spores found in the soil.
Farmers rarely contract the disease and are usually only exposed to Cutaneous
anthrax through open wounds, whereby the bacteria can enter the skin.
Cutaneous anthrax is the form most encountered in naturally occurring cases
and is treatable; it is only deadly in about 20% of untreated cases (Anthrax
on the Farm ). Inhalational anthrax
is very rare and usually fatal; after inhalation of the spores, cold symptoms
set in early and are abruptly followed by respiratory distress and death.
This form is the one used as a bioterrorist weapon. Anthrax can be
treated with antibiotics (ciprofloxacin) if diagnosed early enough, and
it is not a communicable disease. In bioterrorism, anthrax works
well because it is easy to prepare and disperse and can inflict sufficiently
severe disease to paralyze a city and perhaps a nation (Nature's
The Anthrax bacterium produces a toxin which
consists of the three proteins, the protective
antigen (PA), the lethal factor (LF), and
the oedema (OF) factor. These factors along with aa poly-D-glutamic
acid capsule are the major factors imparting virulence in B. anthracis.
The PA < (Heptamer).
Once in the cell, the PA protein is the common binding moiety of two toxins,
lethal and oedema, which are also composed of the lethal factor and the
edema factor proteins (Petosa, 1997).
II. General Structure
The PA monomer <Domain
I (residues 1-258) <Domain
III (residues 488-595) <Domain
IV (residues 596-735) <