RabGDIRabGDP

RabGDIRabGDP refers to the guanine nucleotide dissociation inhibitor (GDI) that binds to the GDP-bound form of Rab GTPases. Rab GTPases are a large family of small molecular weight GTP-binding proteins that regulate intracellular membrane trafficking. RabGDI proteins act as negative regulators of Rab GTPase activity by sequestering Rab proteins in an inactive, GDP-bound state and preventing their association with target membranes.

There are typically multiple RabGDI proteins within a cell, each potentially having some specificity for certain Rab GTPases. The mechanism involves RabGDI binding to the hydrophobic geranylgeranyl lipid modifications present on Rab proteins, effectively shielding them from the membrane and from exchange factors that would promote GDP-GTP exchange. In addition to maintaining Rabs in an inactive state, RabGDIs also play a role in the solubilization and transport of Rab proteins to their appropriate cellular compartments.

Once a Rab GTPase is recruited to a specific organelle membrane, a Rab-specific guanine nucleotide exchange factor (GEF) can displace the GDP, allowing GTP to bind. This GTP-bound form is active and can interact with downstream effector proteins, initiating membrane fusion events or other trafficking processes. The RabGDI then releases the Rab protein, which can then undergo further cycles of activation and inactivation. Dysregulation of RabGDI function can lead to defects in membrane trafficking, which are implicated in various cellular processes and diseases.