title: Structural basis for Rab GTPase activation by VPS9 domain exchange factors.
abstract: RABEX-5 and other exchange factors with VPS9 domains regulate endocytic trafficking through activation of the Rab family GTPases RAB5, RAB21 and RAB22. Here we report the crystal structure of the RABEX-5 catalytic core in complex with nucleotide-free RAB21, a key intermediate in the exchange reaction pathway. The structure reveals how VPS9 domain exchange factors recognize Rab GTPase substrates, accelerate GDP release and stabilize the nucleotide-free conformation. We further identify an autoinhibitory element in a predicted amphipathic helix located near the C terminus of the VPS9 domain. The autoinhibitory element overlaps with the binding site for the multivalent effector RABAPTIN-5 and potently suppresses the exchange activity of RABEX-5. Autoinhibition can be partially reversed by mutation of conserved residues on the nonpolar face of the predicted amphipathic helix or by assembly of the complex with RABAPTIN-5.
authors: Program in Molecular Medicine and Department of Biochemistry & Molecular Pharmacology, University of Massachusetts Medical School, Two Biotech, 373 Plantation Street, Worcester, Massachusetts 01605, USA.
authors: Anna
authors: A
authors: Delprato
authors: David G
authors: DG
authors: Lambright
mesh_terms: D001665:Binding Sites; D018360:Crystallography, X-Ray; D004789:Enzyme Activation; D020662:Guanine Nucleotide Exchange Factors / Q000737:chemistry* / Q000378:metabolism; D006153:Guanosine Diphosphate / Q000378:metabolism; D006801:Humans; D009154:Mutation; D011487:Protein Conformation; D033921:Vesicular Transport Proteins; D020691:rab GTP-Binding Proteins / Q000737:chemistry* / Q000378:metabolism
chemical_list: D020662:Guanine Nucleotide Exchange Factors; C484191:RAB22A protein, human; C097227:RABEP1 protein, human; C108382:RABGEF1 protein, human; D033921:Vesicular Transport Proteins; D006153:Guanosine Diphosphate; D020691:rab GTP-Binding Proteins