Delprato Anna, Lambright David G
Program in Molecular Medicine and Department of Biochemistry & Molecular Pharmacology, University of Massachusetts Medical School, Two Biotech, 373 Plantation Street, Worcester, Massachusetts 01605, USA.
Nat Struct Mol Biol. 2007 May;14(5):406-12. doi: 10.1038/nsmb1232. Epub 2007 Apr 22.
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.
RABEX-5和其他具有VPS9结构域的交换因子通过激活Rab家族GTP酶RAB5、RAB21和RAB22来调节内吞运输。在此，我们报道了RABEX-5催化核心与无核苷酸RAB21（交换反应途径中的关键中间体）形成复合物的晶体结构。该结构揭示了VPS9结构域交换因子如何识别Rab GTP酶底物、加速GDP释放并稳定无核苷酸构象。我们进一步在VPS9结构域C末端附近预测的两亲螺旋中鉴定出一个自抑制元件。该自抑制元件与多价效应物RABAPTIN-5的结合位点重叠，并强烈抑制RABEX-5的交换活性。通过预测的两亲螺旋非极性面上保守残基的突变或与RABAPTIN-5组装复合物，自抑制可部分逆转。
