15 - A Structural and Biochemical Examination of Anthrax Protein Edema Factor
University of Chicago
Edema Factor (EF) is an exotoxin secreted by anthrax-causing bacteria Bacillus anthracis that plays an essential role in the progress of the disease. EF enters the cell by receptor-mediated endocytosis and translocation through the pore of another anthrax protein, protective antigen. Upon entry, EF binds to calmodulin (CaM) and is activated as a potent adenylyl cyclase. Although the structure of calmodulin-bound active EF has been published, the structure of inactive EF has not been definitively determined. To study both the structure and biochemical function of EF, we began with an understanding of the inactive EF€s structure. Because the protein must unfold in order to enter the host cell, EF is recalcitrant to crystallization without the stability provided by CaM and may therefore require chaperones for crystallization. Furthermore, binders that stabilize a particular conformation of the protein may also prevent translocation of EF into the cytosol, making them promising therapeutic targets. Thus we sought to apply new antibody-engineering technology to develop binding reagents that specifically bind EF, made possible by collaboration with the Anthony Kossiakoff group at the University of Chicago. Once appropriate antibodies are found, crystallization will be attempted and diffraction data will be obtained at the Advanced Photon Source at Argonne National Laboratory. Furthermore, the effect of the antibodies on the enzymatic activity and toxicity of EF will be analyzed. Success in these aims will yield not only a structure of CaM-free EF and provide insights towards possible EF-based therapeutic agents against anthrax infection but will also provide a generalized model for the development of antibody-based treatments for recalcitrant targets.