Figure 1.

Small GTPase GTP/GDP cycle. Small GTPases localize in the cytosol as a GDP-bound form under unstimulated conditions. Cell stimulation recruits GDP-bound small GTPases to the vicinity of the plasma membrane and converts these proteins to the GTP-bound form through GEF activity. The GTP-bound form interacts with its specific effectors and thereby transduces signals. GAPs promote the intrinsic GTPase activity of small GTPases and induce conversion of the GTP- to the GDP-bound form. GDIs form a complex with GDP-bound small GTPases and induce their intracellular redistribution from the plasma membrane to the cytosol. GEFs: Guanine nucleotide exchange factors; GAPs: GTPase-activating proteins; GDIs: GDP-dissociation inhibitors.