Proceedings of the National Academy of Sciences of the United States of America, 2011, Vol.108(18), pp.7385-7390
Pore-forming toxins (PFTs) are potent cytolytic agents secreted by pathogenic bacteria that protect microbes against the cell-mediated immune system (by targeting phagocytic cells), disrupt epithelial barriers, and liberate materials necessary to sustain growth and colonization. Produced by gram-positive and gram-negative bacteria alike, PFTs are released as water-soluble monomeric or dimeric species, bind specifically to target membranes, and assemble transmembrane channels leading to cell damage and/or lysis. Structural and biophysical analyses of individual steps in the assembly pathway are essential to fully understanding the dynamic process of channel formation. To work toward this goal, we solved by X-ray diffraction the 2.9-Ã
structure of the 450-kDa heptameric Vibrio cholerae cytolysin (VCC) toxin purified and crystallized in the presence of detergent. This structure, together with our previously determined 2.3-Ã
structure of the VCC water-soluble monomer, reveals in detail the architectural changes that occur within the channel region and accessory lectin domains during pore formation including substantial rearrangements of hydrogen-bonding networks in the pore-forming amphipathic loops. Interestingly, a ring of tryptophan residues forms the narrowest constriction in the transmembrane channel reminiscent of the phenylalanine clamp identified in anthrax protective antigen [Krantz BA, et al. (2005) Science 309:777-781]. Our work provides an example of a Î²-barrel PFT (Î²-PFT) for which soluble and assembled structures are available at high-resolution, providing a template for investigating intermediate steps in assembly. ; p. 7385-7390.
Tryptophan ; Phagocytes ; Vibrio Cholerae ; Detergents ; Gram-Negative Bacteria ; Crystal Structure ; Anthrax Toxin ; Hydrogen Bonding ; Phenylalanine ; Lectins ; X-Ray Diffraction ; Epithelium
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