title: Interaction of the Rho-ADP-ribosylating C3 exoenzyme with RalA.
abstract: RhoA, -B, and -C are ADP-ribosylated and biologically inactivated by Clostridium botulinum C3 exoenzyme and related C3-like transferases. We report that RalA GTPase, which is not ADP-ribosylated by C3, inhibits ADP-ribosylation of RhoA by C3 from C. botulinum (C3bot), Clostridium limosum (C3lim), and Bacillus cereus (C3cer) but not from Staphylococcus aureus (C3stau) in human platelet membranes and rat brain lysate. Inhibition by RalA occurs with the GDP- and guanosine 5'-3-O-(thio)triphosphate-bound forms of RalA and is overcome by increasing concentrations of C3. A direct interaction of RalA with C3 was verified by precipitation of the transferase with GST-RalA-Sepharose. The affinity constant (K(d)) of the binding of RalA to C3lim was 12 nm as determined by fluorescence titration. RalA increased the NAD glycohydrolase activity of C3bot by about 5-fold. Although RalA had no effect on glucosylation of Rho GTPases by Clostridium difficile toxin B, C3bot and C3lim inhibited glucosylation of RalA by Clostridium sordellii lethal toxin. Furthermore, C3bot decreased activation of phospholipase D by RalA. The data indicate that several C3 exoenzymes directly interact with RalA without ADP-ribosylating the GTPase. The interaction is of high affinity and interferes with essential functions of C3 and RalA.
authors.affiliation: Institut für Experimentelle und Klinische Pharmakologie und Toxikologie der Albert-Ludwigs-Universität Freiburg, Otto-Krayer-Haus, Albertstrasse 25, D-79104 Freiburg, Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Wilde
authors.forename: Holger
authors.initials: H
authors.lastname: Barth
authors.forename: Peter
authors.initials: P
authors.lastname: Sehr
authors.forename: Li
authors.initials: L
authors.lastname: Han
authors.forename: Martina
authors.initials: M
authors.lastname: Schmidt
authors.forename: Ingo
authors.initials: I
authors.lastname: Just
authors.forename: Klaus
authors.initials: K
authors.lastname: Aktories
mesh_terms: D036002:ADP Ribose Transferases / Q000378:metabolism*; D000246:Adenosine Diphosphate Ribose / Q000378:metabolism*; D000818:Animals; D001905:Botulinum Toxins / Q000378:metabolism; D002384:Catalysis; D020558:GTP Phosphohydrolases / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D015398:Signal Transduction; D020725:ral GTP-Binding Proteins
chemical_list: D011994:Recombinant Proteins; D000246:Adenosine Diphosphate Ribose; D036002:ADP Ribose Transferases; C063007:exoenzyme C3, Clostridium botulinum; D001905:Botulinum Toxins; D020558:GTP Phosphohydrolases; C492198:RALA protein, human; C492197:Rala protein, rat; D020725:ral GTP-Binding Proteins; D005947:Glucose