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Switch-associated protein-70 Pleckstrin homology (PH) domain SWAP-70 (also called Differentially expressed in FDCP 6/DEF-6 or IRF4-binding protein) functions in cellular signal transduction pathways (in conjunction with Rac), regulates cell motility through actin rearrangement, and contributes to the transformation and invasion activity of mouse embryo fibroblasts. Metazoan SWAP-70 is found in B lymphocytes, mast cells, and in a variety of organs. Metazoan SWAP-70 contains an N-terminal EF-hand motif, a centrally located PH domain, and a C-terminal coiled-coil domain. The PH domain of Metazoan SWAP-70 contains a phosphoinositide-binding site and a nuclear localization signal (NLS), which localize SWAP-70 to the plasma membrane and nucleus, respectively. The NLS is a sequence of four Lys residues located at the N-terminus of the C-terminal a-helix; this is a unique characteristic of the Metazoan SWAP-70 PH domain. The SWAP-70 PH domain binds PtdIns(3,4,5)P3 and PtdIns(4,5)P2 embedded in lipid bilayer vesicles. There are additional plant SWAP70 proteins, but these are not included in this hierarchy. Rice SWAP70 (OsSWAP70) exhibits GEF activity toward the its Rho GTPase, OsRac1, and regulates chitin-induced production of reactive oxygen species and defense gene expression in rice. Arabidopsis SWAP70 (AtSWAP70) plays a role in both PAMP- and effector-triggered immunity. Plant SWAP70 contains both DH and PH domains, but their arrangement is the reverse of that in typical DH-PH-type Rho GEFs, wherein the DH domain is flanked by a C-terminal PH domain. 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.",