Rab geranylgeranyltransferase

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Rab geranylgeranyltransferase (RGGT) is an enzyme that plays a crucial role in the post-translational modification of Rab GTPases. This enzyme is responsible for the geranylgeranylation of Rab proteins, a process that is essential for their proper localization and function within the cell.

Function

Rab geranylgeranyltransferase catalyzes the attachment of geranylgeranyl groups to the cysteine residues at the C-terminus of Rab proteins. This lipid modification is necessary for the association of Rab GTPases with cellular membranes, where they regulate various aspects of vesicle trafficking, including vesicle formation, movement, and fusion.

Structure

RGGT is a heterodimer composed of two subunits: the alpha subunit (RGGTA) and the beta subunit (RGGTB). The enzyme also requires a third component, Rab escort protein (REP), which presents the Rab substrate to RGGT and facilitates the transfer of the geranylgeranyl groups.

Mechanism

The geranylgeranylation process involves the transfer of geranylgeranyl groups from geranylgeranyl pyrophosphate (GGPP) to the cysteine residues of Rab proteins. This reaction is facilitated by the interaction between RGGT, REP, and the Rab substrate. The modified Rab proteins are then able to anchor to cellular membranes and perform their regulatory functions.

Clinical Significance

Mutations or dysregulation of RGGT can lead to various diseases, including choroideremia, a genetic disorder that causes progressive vision loss. Understanding the function and regulation of RGGT is important for developing potential therapeutic strategies for such conditions.

Related Enzymes

RGGT is part of the larger family of prenyltransferases, which also includes farnesyltransferase and geranylgeranyltransferase type I. These enzymes are involved in the prenylation of other small GTPases, such as Ras and Rho proteins.

See Also

• Rab GTPase
• Prenylation
• Vesicle trafficking
• Choroideremia
• Rab escort protein