| A complete understanding of how pathogens interact with their hosts entails understanding the nature of the interactions between pathogen- and host-proteins. Microbial pathogens have evolved many mechanisms to exploit normal host cellular processes in order to promote their own replication or to avoid destruction. In many instances, we know the pathogen protein(s) involved in a particular event, but have not yet identified the host factors or pathways that are targeted. In order to identify host proteins utilized by either viral or bacterial pathogens, a somatic cell genetic approach was utilized to identify mutant cells that were resistant either to retroviral infection or to internalization of anthrax toxin. The studies presented here resulted in the identification of a mutant-cell clone that displays a 100-fold block to murine leukemia virus infection at a step before reverse transcription. More importantly, this work led to the isolation of a mutant-cell clone that lacked the cell surface receptor for anthrax toxin and subsequently to the identification of this receptor as a type I transmembrane protein that is upregulated in tumor endothelium (ATR/TEM8). Anthrax toxin-ATR binding depends on the coordination of a divalent metal ion by ATR through a conserved metal ion dependent adhesion site (MIDAS) motif. Characterization of the molecular determinants for toxin-ATR binding has led to a molecular model of how these two proteins interact. Finally, the discovery of ATR has led to a novel antitoxin approach based on soluble receptor which protects cultured cells from toxin killing. |
