?
 
Bruton's tyrosine kinase pleckstrin homology (PH) domain Btk is a member of the Tec family of cytoplasmic protein tyrosine kinases that includes BMX, IL2-inducible T-cell kinase (Itk) and Tec. Btk plays a role in the maturation of B cells. Tec proteins general have an N-terminal PH domain, followed by a Tek homology (TH) domain, a SH3 domain, a SH2 domain and a kinase domain. The Btk PH domain binds phosphatidylinositol 3,4,5-trisphosphate and responds to signalling via phosphatidylinositol 3-kinase. The PH domain is also involved in membrane anchoring which is confirmed by the discovery of a mutation of a critical arginine residue in the BTK PH domain. This results in severe human immunodeficiency known as X-linked agammaglobulinemia (XLA) in humans and a related disorder is mice.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.",