Guanine nucleotide exchange factor
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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.
- G protein-coupled receptors function as GEFs for their cognate G proteins.