Sandbox 208: Difference between revisions
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= Catalytic mechanism = | = Catalytic mechanism = | ||
[[Image:Catalytic mechanism RabGDI.jpg | thumb | | [[Image:Catalytic mechanism RabGDI.jpg | thumb | 300 px | Model for the catalytic mechanism of RabGDI]] | ||
Initially, Rab is anchored to a target membrane via its lipid moieties. After interactions with its effectors, it returns to the GDP bound form. There is a primary recognition between Rab and GDI: the GTPase domain of Rab is recognized by GDI. GDI binds to Rab via the RBP, forming a low affinity complex. Then, the Rab conserved C terminal AXA box is recognized and bound by the GDI CCR, increasing the complex affinity. Interactions between CCR and the hydrophobic residues of the AXA box lead to a conformation change of the domain II. The GDI lipid binding pocket opens. It is located in the vicinity of the Rab lipid anchor, leading to a favorable situation for lipid transfer. Firstly, the first extracted lipid initially binds to the superficial lipid binding site leading to the formation of a transient high affinity complex still anchored in the membrane. Secondly, this complex is converted into a soluble complex by coordinating transfer of the GDI-bound lipid into the buried binding site. This event facilitates flipping of the second lipid from the membrane to the surface binding site. Thus, a high affinity Rab-GDI complex is formed and released from the membrane. | Initially, Rab is anchored to a target membrane via its lipid moieties. After interactions with its effectors, it returns to the GDP bound form. There is a primary recognition between Rab and GDI: the GTPase domain of Rab is recognized by GDI. GDI binds to Rab via the RBP, forming a low affinity complex. Then, the Rab conserved C terminal AXA box is recognized and bound by the GDI CCR, increasing the complex affinity. Interactions between CCR and the hydrophobic residues of the AXA box lead to a conformation change of the domain II. The GDI lipid binding pocket opens. It is located in the vicinity of the Rab lipid anchor, leading to a favorable situation for lipid transfer. Firstly, the first extracted lipid initially binds to the superficial lipid binding site leading to the formation of a transient high affinity complex still anchored in the membrane. Secondly, this complex is converted into a soluble complex by coordinating transfer of the GDI-bound lipid into the buried binding site. This event facilitates flipping of the second lipid from the membrane to the surface binding site. Thus, a high affinity Rab-GDI complex is formed and released from the membrane. | ||