ABSTRACT
ADP-ribosylation of eukaryotic regulatory proteins is a well-established mechanism by which various bacterial toxins affect the eukaryotic organism. These toxins are capable of transferring the ADP-ribose moiety of NAD to eukaryotic regulatory proteins, which are functionally altered upon introduction of this bulky group. Well-known members of this family of toxins are diphtheria toxin and Pseudomonas exotoxin A, which ADPribosylate elongation factor II, thereby inhibiting protein synthesis (for review see Collier, 1990; Wick and Iglewski, 1990; Pastan and FitzGerald, 1989; Perentesis et al., 1992). A second group of transferases is composed of pertussis toxin (for review see Ui, 1990; Gierschik, 1992), cholera toxin (Fishman, 1990; Gill, 1977; Spangler, 1992), and the largely homologous heat-labile E. coli enterotoxins (Spangler, 1992). This group of ADP-ribosyltransferases modify heterotrimeric G proteins, which are involved in signal transduction. During the last years several clostridial ADP-ribosyltransferases have been described. These toxins can be divided into two groups. One group, which is represented by Clostridium botulinum C2 toxin, Clostridium perfringens iota toxin, Clostridium spiroforme toxin, and an ADP-ribosyltransferase produced by Clostridium difficile, modify actin. The second group with Clostridium botulinum C3 transferase, Clostridium limosum, and the related transferases from Bacillus cereus and Staphylococcus aureus ADP-ribosylate small GTP-binding proteins of the Rho family. In this chapter both classes of clostridial enzymes are described in more detail. During recent years several reviews about clostridial bacterial ADP-ribosyltransferases have been published that focus on actin-ADP-ribosylating toxins (Aktories and Just, 1990; Aktories et al. 1992b; Aktories and Wegner, 1989, 1992; Considine and Simpson, 1991) or on Rho-ADP-ribosylating toxins (Aktories and Hall, 1989; Aktories et al., 1992a) or deal with both toxin families (Aktories, 1990, 1992; Aktories et al. , 1993).
