ADAP (also called centaurin alpha) is a phophatidlyinositide binding protein consisting of an N-terminal ArfGAP domain and two PH domains. In response to growth factor activation, PI3K phosphorylates phosphatidylinositol 4,5-bisphosphate to phosphatidylinositol 3,4,5-trisphosphate. Centaurin alpha 1 is recruited to the plasma membrane following growth factor stimulation by specific binding of its PH domain to phosphatidylinositol 3,4,5-trisphosphate. Centaurin alpha 2 is constitutively bound to the plasma membrane since it binds phosphatidylinositol 4,5-bisphosphate and phosphatidylinositol 3,4,5-trisphosphate with equal affinity. This cd contains the second PH domain repeat. 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.
Feature 1:putative phosphoinositide binding site [chemical binding site]
Comment:binds PIP3 head group (IP4)
Comment:PH2 contains the canonical KXn(K/R)XR motif which is important for high-affinity 3-phosphoinositide-binding, PH1 has a leucine in place of the (K/R) residue, which is not seen in any other known phosphoinositide-binding PH domains