title: Molecular mechanism for Rabex-5 GEF activation by Rabaptin-5.
abstract: Rabex-5 and Rabaptin-5 function together to activate Rab5 and further promote early endosomal fusion in endocytosis. The Rabex-5 GEF activity is autoinhibited by the Rabex-5 CC domain (Rabex-5CC) and activated by the Rabaptin-5 C2-1 domain (Rabaptin-5C21) with yet unknown mechanism. We report here the crystal structures of Rabex-5 in complex with the dimeric Rabaptin-5C21 (Rabaptin-5C212) and in complex with Rabaptin-5C212 and Rab5, along with biophysical and biochemical analyses. We show that Rabex-5CC assumes an amphipathic α-helix which binds weakly to the substrate-binding site of the GEF domain, leading to weak autoinhibition of the GEF activity. Binding of Rabaptin-5C21 to Rabex-5 displaces Rabex-5CC to yield a largely exposed substrate-binding site, leading to release of the GEF activity. In the ternary complex the substrate-binding site of Rabex-5 is completely exposed to bind and activate Rab5. Our results reveal the molecular mechanism for the regulation of the Rabex-5 GEF activity.
authors: State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China.
authors: Zhe
authors: Z
authors: Zhang
authors: State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China.
authors: Tianlong
authors: T
authors: Zhang
authors: State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China.
authors: Shanshan
authors: S
authors: Wang
authors: State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan, China.
authors: Zhou
authors: Z
authors: Gong
authors: State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan, China.
authors: Chun
authors: C
authors: Tang
authors: State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China.
authors: Jiangye
authors: J
authors: Chen
authors: State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China.
authors: Jianping
authors: J
authors: Ding
mesh_terms: D001665:Binding Sites; D001703:Biophysics; D018360:Crystallography, X-Ray; D004705:Endocytosis; D005982:Glutathione Transferase / Q000378:metabolism; D020662:Guanine Nucleotide Exchange Factors / Q000378:metabolism*; D006801:Humans; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D053838:Scattering, Small Angle; D014357:Trypsin / Q000737:chemistry; D033921:Vesicular Transport Proteins / Q000378:metabolism*; D014961:X-Ray Diffraction
chemical_list: D020662:Guanine Nucleotide Exchange Factors; C097227:RABEP1 protein, human; C108382:RABGEF1 protein, human; D033921:Vesicular Transport Proteins; D005982:Glutathione Transferase; D014357:Trypsin
keywords: E. coli; GEF activity; Rab5; Rabaptin-5; biochemistry; biophysics; crystal structure; human; molecular mechanism; rabex-5; structural biology