Abstract 1119 Characterizing the Membrane-Inserted Conformation of a Bacterial Toxin Delivery Protein

Contact-dependent inhibition (CDI) systems mediate interbacterial competition between Gram-negative bacteria. These CDI systems are produced by a broad group of organisms and utilize a cell surface protein, CdiA, to deliver a protein toxin into neighboring cells. CdiA binds to a receptor in the outer membrane of the target cell and translocates the toxin across that membrane without any external energy source. The mechanism of the toxin transport is not well understood but could suggest new ways of delivering antibiotics across the outer membranes of Gram-negative bacteria. We have used cysteine and photocrosslinking to characterize how an E. coli CdiA interacts with its receptor, BamA, as it assembles into the target cell's outer membrane. Our data suggest that CdiA may adopt an extended beta-sheet structure and be positioned near the lateral gate in BamA's beta-barrel. Ongoing investigations aim to characterize the structure of the membrane-embedded regions of these proteins to further our understanding of the translocation process. I would like to acknowledge the College of the Holy Cross and the Cottrell Scholar Award #28179 sponsored by Research Corporation for Science Advancement for funding this research.