Rab-eiwitten

Membrane recognition by vesicles is coordinated by a group of monomeric GTPases called Rabs. The sequential activation and deactivation of Rabs create a cascade to guide vesicles to the target membrane.

Rabs switch reversibly between a GDP-bound inactive state and a GTP-bound active state with the help of Rab-Guanine nucleotide exchange factors or Rab-GEFs and Rab-GTPase activating proteins or Rab-GAPs.

In the cytosol, Rab-GDP is associated with the GDP dissociation inhibitor, or GDI, that keeps it inactive.

On the target membrane, Rab-GEF activates Rab by replacing the GDP with GTP and inducing a conformational change that inserts Rab in the membrane. A Rab effector binds to Rab-GTP, anchoring the complex to the membrane.

If a Rab-GTP is not bound to an effector, Rab-GAP can facilitate GTP hydrolysis, thus deactivating the Rab.