The protective antigen (PA) of Bacillus anthracis is integral to the mechanism of anthrax poisoning. The cloning, expression and purification of a 32 kDa B. anthracis PA fragment (PA32) is described. This fragment has also been expressed as a fusion construct to stabilized green fluorescent protein (EGFP-PA32). Both proteins were capable of binding to specific cell surface receptors as determined by fluorescent microscopy and a flow cytometric assay. To confirm binding specificity in the flow cytometric assay, non-fluorescent PA83 or PA32 was used to competitively inhibit fluorescent EGFP-PA32 binding to cell receptors. This assay can be employed as a rapid screen for compounds which disrupts binding of PA to cells. Additionally, the high intracellular expression levels and ease of purification make this recombinant protein an attractive vaccine candidate or therapeutic treatment for anthrax poisoning.
FIELD OF THE INVENTION
The present invention relates generally to inhibiting anthrax toxicity and, more particularly, to the identification of human antibodies which bind to the protective antigen (PA83) of Bacillus anthracis, thereby disrupting cell receptor binding thereof. This invention was made with government support under Contract No. W-7405-ENG-363 awarded by the U.S. Department of Energy to The Regents of The University of California. The government has certain rights in the invention.