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Dock Homology Region 2, a GEF domain, of Class C Dedicator of Cytokinesis 6 Dock6, also called Zizimin-related 1 (Zir1), is an atypical guanine nucleotide exchange factor (GEF) that lacks the conventional Dbl homology (DH) domain. As a GEF, it activates the small GTPases Rac and Cdc42 by exchanging bound GDP for free GTP. It is widely expressed and shows highest expression in the dorsal root ganglion and the brain. It regulates neurite outgrowth. DOCK proteins are divided into four classes (A-D) based on sequence similarity and domain architecture; class C includes Dock6, 7 and 8. All DOCKs contain two homology domains: the DHR-1 (Dock homology region-1), also called CZH1 (CED-5, Dock180, and MBC-zizimin homology 1), and DHR-2 (also called CZH2 or Docker). The DHR-1 domain binds phosphatidylinositol-3,4,5-triphosphate. This alignment model represents the DHR-2 domain of Dock6, which contains the catalytic GEF activity for Rac and/or Cdc42.
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