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BCR downstream signaling 1 Pleckstrin homology (PH) domain Brdg1 is thought to function as a docking protein acting downstream of Tec, a protein tyrosine kinases (PTK), in B-cell antigen receptor (BCR) signaling. BRDG1 contains a proline-rich (PR) motif which is thought to bind SH3 or WW domains, a PH domain, and multiple tyrosine residues which are potential target sites for SH2 domains. Since PH domains bind phospholipids it is thought to be involved in the tethering of Tec and BRDG1 to the cell membrane.Tec and Pyk2, but not Btk, Bmx, Lyn, Syk, or c-Abl, induces phosphorylation of BRDG1 on tyrosine residues. Efficient phosphorylation requires both the PH and SH2 domains of BRDG1 and the kinase domain of Tec. The overexpression of BRDG1 increases theBCR-mediated activation of cAMP-response element binding protein (CREB). Phosphorylated BRDG1 is hypothesized to recruit CREB either directly or through its recruitment of downstream effectors which then recruit CREB. 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.",