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Dedicator of cytokinesis-D subfamily Pleckstrin homology (PH) domain DOCK-D subfamily (also called Zizimin subfamily) consists of Dock9/Zizimin1, Dock10/Zizimin3, and Dock11/Zizimin2. DOCK-D has a N-terminal DUF3398 domain, a PH-like domain, a Dock Homology Region 1, DHR1 (also called CZH1), a C2 domain, and a C-terminal DHR2 domain (also called CZH2). Zizimin1 is enriched in the brain, lung, and kidney; zizimin2 is found in B and T lymphocytes, and zizimin3 is enriched in brain, lung, spleen and thymus. Zizimin1 functions in autoinhibition and membrane targeting. Zizimin2 is an immune-related and age-regulated guanine nucleotide exchange factor, which facilitates filopodial formation through activation of Cdc42, which results in activation of cell migration. No function has been determined for Zizimin3 to date. The N-terminal half of zizimin1 binds to the GEF domain through three distinct areas, including CZH1, to inhibit the interaction with Cdc42. In addition its PH domain binds phosphoinositides and mediates zizimin1 membrane targeting. DOCK is a family of proteins involved in intracellular signalling networks. They act as guanine nucleotide exchange factors for small G proteins of the Rho family, such as Rac and Cdc42. There are 4 subfamilies of DOCK family proteins based on their sequence homology: A-D. PH domains have diverse functions, but in general are involved in targeting proteins to the appropriate cellular location or in the interaction with a binding partner. They share little sequence conservation, but all have a common fold, which is electrostatically polarized. Less than 10% of PH domains bind phosphoinositide phosphates (PIPs) with high affinity and specificity. PH domains are distinguished from other PIP-binding domains by their specific high-affinity binding to PIPs with two vicinal phosphate groups: PtdIns(3,4)P2, PtdIns(4,5)P2 or PtdIns(3,4,5)P3 which results in targeting some PH domain proteins to the plasma membrane. A few display strong specificity in lipid binding. Any specificity is usually determined by loop regions or insertions in the N-terminus of the domain, which are not conserved across all PH domains. PH domains are found in cellular signaling proteins such as serine/threonine kinase, tyrosine kinases, regulators of G-proteins, endocytotic GTPases, adaptors, as well as cytoskeletal associated molecules and in lipid associated enzymes. |
Jiyao W et al.(2023). "The conserved domain database in 2023.",