Guanine nucleotide exchange factor

Overview
Guanine nucleotide exchange factor (or guanine exchange protein) (GEFs) is implicated in addressing system of vesicular transport. For example, Rab is GDP-bound and inactive in the cytosol before contact with GEF. The membrane-bound GEF catalyses the removal of GDP and GDI (GDP dissociation inhibitor) and their replacement with GTP. This allows the Rab protein to bind budding vesicles (e.g., clathrin-coated vesicles). Un-coating of the vesicle allows an interaction between Rab and Rab effector (at the target site), which aids SNARE protein interactions.

Examples of GEFs

 * SOS - Son of Sevenless is a GEF that is important in the cell growth-regulatory MAPK/ERK pathway.


 * eIF-2b - The eukaryotic initiation factor 2b regenerates eIF-2a for an additional cycle in protein synthesis initiation, i.e., its binding to the Met-t-RNA.


 * Ras-GRF1


 * G protein-coupled receptors function as GEFs for their cognate G proteins.


 * Kalirin