title: Crystal structure of the Vibrio cholerae cytolysin heptamer reveals common features among disparate pore-forming toxins.
abstract: 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-Å 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-Å 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 β-barrel PFT (β-PFT) for which soluble and assembled structures are available at high-resolution, providing a template for investigating intermediate steps in assembly.
authors.affiliation: Department of Molecular Biology and Biochemistry, Wesleyan University, 52 Lawn Avenue, Middletown, CT 06459, USA.
authors.forename: Swastik
authors.initials: S
authors.lastname: De
authors.forename: Rich
authors.initials: R
authors.lastname: Olson
mesh_terms: D000595:Amino Acid Sequence; D003460:Crystallization; D008958:Models, Molecular; D008969:Molecular Sequence Data; D052899:Pore Forming Cytotoxic Proteins / Q000737:chemistry* / Q000302:isolation & purification*; D011487:Protein Conformation; D014734:Vibrio cholerae / Q000737:chemistry*; D014961:X-Ray Diffraction
chemical_list: D052899:Pore Forming Cytotoxic Proteins