Figure 2.

The cycle of Rab GTPase activation. Newly synthesised de novo Rab GTPases interact with Rab escort protein (REP), which enables prenylation via geranylgeranyltransferase (GGTase). When active, Rab GTPases are bound to GTP and associated with their target membrane. Following hydrolysis of GTP to GDP, they become inactive and reside in the cytosol. The Rab GTPase activation cycle is aided by a number of effectors. GTPase activating proteins (GAPs) catalyse the hydrolysis of GTP to GDP to inactivate the Rab. GDP dissociation inhibitors (GDIs) retrieve the inactive Rab from the membrane and solubilises it in the cytosol. However, guanine exchange factors (GEFs) catalyse the exchange of GDP with GTP, thus reactivating the Rab [12].