Actin ADP-ribosylation

C. botulinum C2-toxin and related toxins Actin ADP-ribosylation Inhibition of actin polymerization... 

Barth H, Blocker D, Aktories K. The uptake machinery of clostridial actin ADP-ribosylating toxins—a cell delivery system for fusion proteins and polypeptide drugs. Naunyn Schmiedebergs Arch Pharmacol 2002 366(6) 501-512. 

Clostridium botulinum C2 toxin The prototype of a binary actin-ADP-ribosylating toxin 155... 

Potent Virulence Factors Directly Attack the Actin Cytoskeleton of Mammalian Cells Actin-ADP-Ribosylating Toxins... 

Figure 2 The actin-ADP-ribosylating toxins, (a) Molecular mode of action. The actin-ADP-ribosylating toxins covalently transfer an ADP-ribose moiety from NAD+ onto Arg177 of G-actin in the cytosol of targeted cells. Mono-ADP-ribosylated G-actin acts as a capping protein and inhibits the assembly of nonmodified actin into filaments. Thus, actin polymerization is blocked at the fast-growing ends of actin filaments (plus or barbed ends) but not at the slow growing ends (minus or pointed ends). This effect ultimately increases the critical concentration necessary for actin polymerization and tends to depolymerize F-actin. Finally, all actin within an intoxicated cell becomes trapped as ADP-ribosylated G-actin.

In 1980, C. botulinum C2 toxin was the first binary actin-ADP-ribosylating toxin to be described in the literature. The C2 toxin, produced by C. botulinum types C and D, consists of two nonlinked components... 

Actin-ADP-ribosylating Toxins Cytotoxic Mechanisms of Clostridium botulinum C2 Toxin and Clostridium perfringens lota Toxin... 

ADP-ribosylation of actin depends on the native structure of the protein substrate. In the presence of EDTA, which chelates and removes the actin-bound magnesium ion, resulting in denaturation of actin, ADP-ribosylation is completely blocked (Just ef al., 1990). C. botulinum C2 toxin or C. perfringens iota toxin ADP-ribosylate monomeric G-actin, but not polymerized F-actin (Aktories et al., 1986b Schering et al., 1988). This is due to the fact that the acceptor amino acid arginine-177, which is located in domain III of actin, is at or near... 

Fig. 2. Model of the cytopathic effects of actin ADP-ribosylating toxins. The activated binding component of C. botulinum C2 toxin binds to a receptor of the eukaryotic cell. This induces a binding site for the enzyme component (C2I), Most likely, C2I enters the cell by endocytosis and subsequent translocation. In the cell, G-actin is ADP-ribosylated, which inhibits its polymerization and traps actin in the monomeric form. ADP-ribosylated actin binds in a capping protein-like manner to the barbed ends of filaments to inhibit further polymerization at the fast-growing end of F-acfin. The foxin has no effects on the pointed end of filaments where actin depolymerization takes place. Additionally, ADP-ribosylation may affect functions of complexes of acfin wifh binding proteins as examplified in Fig. 1 (From (Aktories, 1990) with permission)...

Table 2. Effects of actin ADP-ribosylating toxins on the cytoskeleton... 

Aktories K, Wille M, Just I (1992) Clostridial actin-ADP-ribosylating toxins. In Curr. Top. Microbiol. Immunol. 175 97-113... 

Aktories K, Wegner A (1992) Mechanisms of the cytopathic action of actin-ADP-ribosylating toxins. In Mol. Microbiol. 6 2905-8... 

Weigt C, Just I, Wegner A et al. (1989) Nonmuscle actin ADP-ribosylated by botuli-num C2 toxin cops actin filaments. In FEBS Lett. 246 181 -4 Wiegers W, Just I, Moller H et al. (1991) Alteration of the cytoskeleton of mammalian cells cultured in vitro by Clostridium botulinum C2 toxin and C3 ADP-ribosyltransferase. In Eur. J. Cell Biol. 54 237-45 Wille M, Just I, Wegner A et al. (1992) ADP-ribosylation of the gelsolin-actin complex by clostridial toxins. In J. Biol. Chem. 267 50-5... 

C. botulinum C2 toxin and C perfringens iota toxin belong to the family of actin-ADP-ribosylating toxins that transfer ADP-ribose from NAD to arginine-177 of actin. This modification results in inhibition of actin polymerization, leading to depolymerization of the microfilament network. Origin, structure, molecular mechanisms and general aspects of the use of this family of toxins is described in chapter 8, 9 and 10. 

The proteins are separated by 11 % SDS gel electrophoresis and labeled actin (42kDa) is analyzed by autoradiography or phosphorimaging. The difference in ADP-ribosylation between control and toxin-treated cells gives the proportion of actin ADP-ribosylated in the intact cell. 

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