Historical Background and Taxonomy
Rac GTPases comprise one of the eight subfamilies of the Rho (Ras homology) GTPases family, itself a subgroup of the Ras superfamily of small G proteins (Burridge and Wennerberg 2004). They were first identified as a substrate for the bacterial C3-like transferases that block Rho by ADP-ribosylation, although the C3-like transferases act on Rac rather inefficiently. More effective are the large clostridial cytotoxins (with prototypes the Clostridium difficile toxin A and B) which glycosylate Rac at Thr35, inhibiting its functions by preventing effector coupling (Aktories et al. 2000). Rac GTPases are preferred targets for bacteria since they act as molecular switches in a multitude of signaling processes, regulating many fundamental cellular functions, including actin cytoskeleton, cell adhesion, motility and migration, vesicular transport pathways and cytokinesis, reactive oxygen species (ROS)production via NADPH oxidase, as well as cell...
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