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target organelle

Saturday 3 June 2006

Targeting and Fusion of Vesicles with the Target Organelle

The Rab proteins are key regulators of the tethering and fusion of vesicles during vesicle transport. They cycle between forms bound by guanosine triphosphate (GTP) and guanosine diphosphate (GDP) and shift between cellular membranes and the cytoplasm with the help of the Rab GDP-dissociation inhibitor (GDI).

The membrane association of Rab proteins is dependent on hydrophobic modification mediated by Rab escort protein (REP) and an isoprenyl transferase.

The function of Rab guanosine triphosphatases (GTPases) and their effectors is apparently linked to that of the highly conserved membrane-anchored proteins (SNAREs) acting farther downstream in the vesicle fusion process.

The pairing of these proteins on the vesicle and target membranes is needed for bilayer fusion.

Examples of genetic defects that affect the function of Rab proteins include choroideremia, in which Rab escort protein 1 is defective, and X-linked mental retardation, in which the Rab GDP-dissociation inhibitor is defective.


- Olkkonen VM, Ikonen E. Genetic defects of intracellular-membrane transport. N Engl J Med. 2000 Oct 12;343(15):1095-104. PMID: 11027745