Molecular mechanism for Rabex-5 GEF activation by Rabaptin-5

• DOI: 10.7554/elife.02687
• Publication Date: 2014-06-23T15:18:13Z
• Authors: Zhe Zhang; Tianlong Zhang; Shanshan Wang; Zhou Gong; Chun Tang; Jiangye Chen; Jianping Ding
• Keywords: 0301 basic medicine; crystal structure; QH301-705.5; Science; Biophysics; Vesicular Transport Proteins; Crystallography, X-Ray; Biochemistry; 03 medical and health sciences; Rab5; X-Ray Diffraction; Scattering, Small Angle; Guanine Nucleotide Exchange Factors; Humans; Trypsin; Biology (General); Glutathione Transferase; Binding Sites; Q; R; Endocytosis; Protein Structure, Tertiary; 3. Good health; rabex-5; Medicine; Rabaptin-5; GEF activity; molecular mechanism; Protein Binding

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.