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Actin filament associated protein family Pleckstrin homology (PH) domain, repeat 2 There are 3 members of the AFAP family of adaptor proteins: AFAP1, AFAP1L1, and AFAP1L2/XB130. AFAP1 is a cSrc binding partner and actin cross-linking protein. AFAP1L1 is thought to play a similar role to AFAP1 in terms of being an actin cross-linking protein, but it preferentially binds to cortactin and not cSrc, thereby playing a role in invadosome formation. AFAP1L2 is a cSrc binding protein, but does not bind to actin filaments. AFAP1L2 acts as an intermediary between the RET/PTC kinase and PI-3kinase pathway in the thyroid. The AFAPs share a similar structure of a SH3 binding motif, 3 SH2 binding motifs, 2 PH domains, a coiled-coil region corresponding to the AFAP1 leucine zipper, and an actin binding domain. This cd is the second PH domain of AFAP. 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.",