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Grb2-associated binding protein family Pleckstrin homology (PH) domain Gab proteins are scaffolding adaptor proteins, which possess N-terminal PH domains and a C-terminus with proline-rich regions and multiple phosphorylation sites. Following activation of growth factor receptors, Gab proteins are tyrosine phosphorylated and activate PI3K, which generates 3-phosphoinositide lipids. By binding to these lipids via the PH domain, Gab proteins remain in proximity to the receptor, leading to further signaling. While not all Gab proteins depend on the PH domain for recruitment, it is required for Gab activity. There are 3 families: Gab1, Gab2, and Gab3. 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.",