Vesicular transport during exocytosis is regulated by Rab GTPase (Sec4p in yeast), which is activated by a guanine nucleotide exchange factor (GEF) called Sec2p. Here, we report the crystal structure of the Sec2p GEF domain in a complex with the nucleotide-free Sec4p at 2.7 A resolution. Upon complex formation, the Sec2p helices approach each other, flipping the side chain of Phe-109 toward Leu-104 and Leu-108 of Sec2p. These three residues provide a hydrophobic platform to attract the side chains of Phe-49, Ile-53, and Ile-55 in the switch I region as well as Phe-57 and Trp-74 in the interswitch region of Sec4p. Consequently, the switch I and II regions are largely deformed, to create a flat hydrophobic interface that snugly fits the surface of the Sec2p coiled coil. These drastic conformational changes disrupt the interactions between switch I and the bound guanine nucleotide, which facilitates the GDP release. Unlike the recently reported 3.3 A structure of the Sec4p.Sec2p complex, our structure contains a phosphate ion bound to the P-loop, which may represent an intermediate state of the nucleotide exchange reaction.
|Evidence ID||Analyze ID||Interactor||Interactor Systematic Name||Interactor||Interactor Systematic Name||Type||Assay||Annotation||Action||Modification||Phenotype||Source||Reference||Note|
|Evidence ID||Analyze ID||Gene||Gene Systematic Name||Gene Ontology Term||Gene Ontology Term ID||Qualifier||Aspect||Method||Evidence||Source||Assigned On||Reference||Annotation Extension|
|Evidence ID||Analyze ID||Gene||Gene Systematic Name||Phenotype||Experiment Type||Experiment Type Category||Mutant Information||Strain Background||Chemical||Details||Reference|
|Evidence ID||Analyze ID||Regulator||Regulator Systematic Name||Target||Target Systematic Name||Experiment||Conditions||Strain||Source||Reference|