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Dock Homology Region 2, a GEF domain, of Class D Dedicator of Cytokinesis proteins DOCK proteins are atypical guanine nucleotide exchange factors (GEFs) that lack the conventional Dbl homology (DH) domain. As GEFs, they activate small GTPases by exchanging bound GDP for free GTP. They are divided into four classes (A-D) based on sequence similarity and domain architecture; class D, also called the Zizimin subfamily, includes Dock9, 10 and 11. Class D Docks are specific GEFs for Cdc42. Dock9 plays important roles in spine formation and dendritic growth. Dock10 and Dock11 are preferentially expressed in lymphocytes. 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 class D DOCKs, which contains the catalytic GEF activity for Cdc42. Class D DOCKs also contain a Pleckstrin homology (PH) domain at the N-terminus.
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