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Pleckstrin homology domain in BEACH domain containing proteins The BEACH domain is present in several eukaroyotic proteins CHS, neurobeachin (Nbea), LRBA (also called BGL, beige-like, or CDC4L), FAN, KIAA1607, and LvsA-LvsF. CHS is a rare, autosomal recessive disorder that can cause severe immunodeficiency and albinism in mammals and beige is the name for the CHS disease in mice. The CHS disease is associated with the presence of giant, perinuclear vesicles (lysosomes, melanosomes, and others) and CHS protein is thought to play an important role in the fusion, fission, or trafficking of these vesicles. All BEACH proteins contain the following domains: PH, BEACH, and WD40. The WD40 domain is involved in mediating protein-protein interactions involved in targeting proteins to subcellular compartments. The combined PH-BEACH motifs may present a single continuous structural unit involved in protein binding. Some members have an additional N-terminal Laminin G-like (LamG) domains Ca++ mediated receptors or an additional C-terminal FYVE zinc-binding domain which targets proteins to membrane lipids via interaction with phosphatidylinositol-3-phosphate, PI3P. 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.
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