Bacterial ADP-ribosylating toxins: molecular structures and signal transducing functions

Mono-ADP-ribosylation is a posttranslational modification of proteins employed by a variety of bacterial ADP-ribosylating toxins to modify the metabolism of target cells. The ADP-ribosyltransferases of bacterial toxins, in general, use NAD as a substrate for covalent modification by ADP-ribose to certain GTP-binding proteins (G proteins) as signal transducers resulting in altered enzymatic activity of the membrane enzymes as effectors. Such a mechanism has the potential of being of importance in the physiological regulation of cellular metabolism, particularly if the process is reversible. These ADP-ribosylating toxins are characterized in Table 1.