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Dock Homology Region 2, a GEF domain, of Class C Dedicator of Cytokinesis 8 Dock8, also called Zizimin-related 3 (Zir3), is an atypical guanine nucleotide exchange factor (GEF) that lacks the conventional Dbl homology (DH) domain. As a GEF, it activates the small GTPases Rac1 and Cdc42 by exchanging bound GDP for free GTP. Dock8 is highly expressed in the immune system and it regulates T and B cell numbers and functions. It plays essential roles in humoral immune responses and the proper formation of B cell immunological synapses. Dock8 deficiency is a primary immune deficiency that results in extreme susceptibility to cutaneous viral infections, elevated IgE levels, and eosinophilia. It was originally described as an autosomal recessive form of hyper IgE syndrome (AR-HIES). 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 Dock8, which contains the catalytic GEF activity for Rac and/or Cdc42. |
Jiyao W et al.(2023). "The conserved domain database in 2023.",