title: Structure and action of the binary C2 toxin from Clostridium botulinum.
abstract: C2 toxin from Clostridium botulinum is composed of the enzyme component C2-I, which ADP-ribosylates actin, and the binding and translocation component C2-II, responsible for the interaction with eukaryotic cell receptors and the following endocytosis. Three C2-I crystal structures at resolutions of up to 1.75 A are presented together with a crystal structure of C2-II at an appreciably lower resolution and a model of the prepore formed by fragment C2-IIa. The C2-I structure was determined at pH 3.0 and at pH 6.1. The structural differences are small, indicating that C2-I does not unfold, even at a pH value as low as 3.0. The ADP-ribosyl transferase activity of C2-I was determined for alpha and beta/gamma-actin and related to that of Iota toxin and of mutant S361R of C2-I that introduced the arginine observed in Iota toxin. The substantial activity differences between alpha and beta/gamma-actin cannot be explained by the protein structures currently available. The structure of the transport component C2-II at pH 4.3 was established by molecular replacement using a model of the protective antigen of anthrax toxin at pH 6.0. The C-terminal receptor-binding domain of C2-II could not be located but was present in the crystals. It may be mobile. The relative orientation and positions of the four other domains of C2-II do not differ much from those of the protective antigen, indicating that no large conformational changes occur between pH 4.3 and pH 6.0. A model of the C2-IIa prepore structure was constructed based on the corresponding assembly of the protective antigen. It revealed a surprisingly large number of asparagine residues lining the pore. The interaction between C2-I and C2-IIa and the translocation of C2-I into the target cell are discussed.
authors.affiliation: Institut für Organische Chemie und Biochemie, Albert-Ludwigs-Universität, Albertstr. 21, D-79104 Freiburg im Breisgau, Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Schleberger
authors.forename: Henrike
authors.initials: H
authors.lastname: Hochmann
authors.forename: Holger
authors.initials: H
authors.lastname: Barth
authors.forename: Klaus
authors.initials: K
authors.lastname: Aktories
authors.forename: Georg E
authors.initials: GE
authors.lastname: Schulz
mesh_terms: D036002:ADP Ribose Transferases / Q000737:chemistry / Q000378:metabolism; D000199:Actins / Q000378:metabolism; D000941:Antigens; D001216:Asparagine; D001665:Binding Sites; D001905:Botulinum Toxins / Q000737:chemistry*; D003014:Clostridium botulinum / Q000737:chemistry*; D018360:Crystallography, X-Ray; D006863:Hydrogen-Ion Concentration; D015394:Molecular Structure
chemical_list: D000199:Actins; D000941:Antigens; D001216:Asparagine; D036002:ADP Ribose Transferases; D001905:Botulinum Toxins