The symptoms of many bacterial diseases are due largely to the actions of toxic proteins released by the bacteria (diphtheria, anthrax, cholera, and tetanus toxins are well known examples). We study these toxins with the general goal of understanding the biochemical basis of bacterial disease, and also to gain insight into how proteins insert into and cross membranes, and to develop new vaccines based on novel properties of these toxins. The most potent bacterial toxins act by penetrating into mammalian cells and covalently modifying target substrates within the cytosol. Their actions generally involve four steps: (i) binding to receptors; (ii) receptor-mediated endocytosis; (iii) translocation of the enzymic moiety across a membrane, into the cytosol; and (iv) enzymic modification of a target substrate. We are currently focusing on diphtheria and anthrax toxins, applying biophysical, biochemical, and cell biological methods to generate detailed models of each step in toxin action. How these structurally unrelated toxins insert into bilayers under the influence of the low pH of the endosomal compartment, and translocate their enzymic moieties across the endosomal membrane represents a problem of interest from many perspectives. Crystallographic structures of the native proteins provide a framework for our studies. Genetically modified, nontoxic forms of these toxins may be used as transporters for heterologous proteins and peptides into cells. We are using anthrax toxin to engineer a new type of vaccines that stimulates the formation of cytotoxic T lymphocytic (CTL) responses, as opposed to antibody formation. CTL-based vaccines may be useful against a variety of diseases which have heretofore been thought to be beyond the realm of vaccination.
Selected Publications:
Ballard, J. D., R. J. Collier, and M. N. Starnbach. (1996). Anthrax Toxin-Mediated Delivery Of a Cytotoxic T-Cell Epitope In Vivo. Proc.Natl. Acad. Sci. USA 93:12531-12534.
Petosa, C., R. J. Collier, K. R. Klimpel, S. H. Leppla, and R. C. Liddington. (1997). Crystal structure of the anthrax toxin protective antigen. Nature. 385:833-838.
Benson, E.L., P.D. Huynh, A. Finkelstein, and R.J. Collier. 1998. Identification
of residues lining the
anthrax protective antigen channel. Biochemistry. 37:3941-3948.