Regulation of phagocyte function by low molecular weight GTP-binding proteins

The mechanisms used by phagocytic leukocytes in the process of bacterial killing are regulated by GTP-binding proteins of the Ras superfamily. In particular, the formation of toxic oxygen metabolites via the NADPH oxidase requires the action of both Rac and Rap1A proteins. Rac2 forms a third cytosolic component of the human neutrophil NADPH oxidase. Rac2 is active in its GTP-bound form, and requires post-translational processing (isoprenylation) in order to interact with regulatory proteins which stimulate the exchange of GTP for GDP. In the resting neutrophil, Rac is localized to the cytosol in the form of a complex with a GDP dissociation inhibitor (GDI) protein. Upon cell activation, this complex is disrupted to enable Rac to translocate to the active oxidase at the plasma membrane. The Rac-GDI complex may be regulated by the release of specific lipids known to be generated during phagocyte activation.