David Auble
Rab GTPases control multiple steps in intracellular vesicle trafficking. They are active when bound to GTP and inactive when bound to GDP. The switch from the active to inactive state primarily involves conformational changes in the nucleotide binding site, and the interconversion is catalyzed by guanine nucleotide exchange factors (GEFs), which catalyze the exchange of GDP for GTP. A coiled coil region in the GEF Sec2 is necessary and sufficient for GEF activity in vivo. This region of Sec2 interacts physically with the Rab GTPase Sec4. Here you can see how a remarkable 160 residue/ 220 angstrom long parallel coiled coil region of Sec2 interacts with Sec4 (2ocy). The Sec4 binding site on Sec2 is provided by a surface resulting from a marked deviation of the canonical coiled coil structure. The binding of Sec2 induces conformational changes in the nucleotide binding pocket of Sec4, providing a molecular explanation for GEF activity. The display allows you to highlight residues in the protein-protein interface. Despite the elongated and thin shape of Sec2, the hydrophobic Sec2-Sec4 interaction surface is >3000 square angstroms.
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Sec2 monomers are blue and magenta. Sec4 is gray.
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