Rab (G-protein)

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Rab (G-protein)

Rab proteins are a family of small GTPases that are key regulators of intracellular transport. They are part of the larger Ras superfamily of GTPases. Rab proteins are involved in various stages of vesicle trafficking, including vesicle formation, movement along actin and microtubule filaments, and membrane fusion.

Structure and Function

Rab proteins are characterized by their ability to bind and hydrolyze GTP. They cycle between an active GTP-bound state and an inactive GDP-bound state. In their active form, Rab proteins interact with a variety of effector proteins to regulate different steps of vesicle trafficking. Each Rab protein is associated with specific intracellular membranes, such as the Golgi apparatus, endosomes, and plasma membrane.

Rab Protein Family

The Rab protein family is one of the largest families within the Ras superfamily, with over 60 members identified in humans. Some well-known Rab proteins include:

• Rab1: Involved in transport between the endoplasmic reticulum and the Golgi apparatus.
• Rab5: Plays a role in early endosome dynamics.
• Rab7: Regulates late endosome and lysosome function.
• Rab11: Associated with recycling endosomes.

Mechanism of Action

Rab proteins function as molecular switches. In their GTP-bound state, they recruit specific effector proteins that facilitate vesicle budding, motility, tethering, and fusion. The conversion from the GTP-bound to the GDP-bound state is regulated by GTPase-activating proteins (GAPs), which accelerate GTP hydrolysis, and guanine nucleotide exchange factors (GEFs), which promote the exchange of GDP for GTP.

Clinical Significance

Mutations in Rab proteins or their regulatory components can lead to various diseases. For example, mutations in Rab27a are associated with Griscelli syndrome, a rare genetic disorder that affects pigmentation and immune function. Additionally, Rab proteins have been implicated in neurodegenerative diseases such as Parkinson's disease.

Research and Applications

Rab proteins are studied extensively in cell biology and medicine. They serve as important markers for different intracellular compartments and are used to understand the mechanisms of vesicle trafficking. Research on Rab proteins also provides insights into the pathogenesis of diseases and potential therapeutic targets.

See Also

• GTPase
• Vesicle trafficking
• Ras superfamily
• Endosome
• Golgi apparatus