ADP-ribosylation of actin by clostridial toxins

umber of clostridial bacteria produce toxins which ADP-ribosylate monomeric actin. These include botulinum C2 toxin (2), Clostridiumperfringens iota toxin (23, 26), Clostridium spiroforme toxin (20, 27), and an ADP-ribosyltransferase produced by Clostridium difficile (21). The toxins have turned out to be valuable tools for investigating the actin cytoskeleton since ADP-ribosylation of actin blocks its polymerization. Furthermore, ADP-ribosylated actin acts as a capping protein that binds to the fast-growing barbed end of polymerized F-actin to further inhibit polymerization of nonmodified actin. This class of newly isolated toxins can be used to investigate the dynamic turnover of Gand F-actin in living cells. The best studied example of these new toxins is botulinum C2 toxin, which is described in this review in more detail.