PLC-gamma (PLCgamma) is activated by receptor and non-receptor tyrosine kinases due to the presence of its SH2 and SH3 domains. There are two main isoforms of PLC-gamma expressed in human specimens, PLC-gamma1 and PLC-gamma2. PLC-gamma consists of an N-terminal PH domain, a EF hand domain, a catalytic domain split into X and Y halves internal to which is a PH domain split by two SH2 domains and a single SH3 domain, and a C-terminal C2 domain. Only the first PH domain is present in this hierarchy. PLCs (EC 3.1.4.3) play a role in the initiation of cellular activation, proliferation, differentiation and apoptosis. They are central to inositol lipid signalling pathways, facilitating intracellular Ca2+ release and protein kinase C (PKC) activation. Specificaly, PLCs catalyze the cleavage of phosphatidylinositol-4,5-bisphosphate (PIP2) and result in the release of 1,2-diacylglycerol (DAG) and inositol 1,4,5-triphosphate (IP3). These products trigger the activation of protein kinase C (PKC) and the release of Ca2+ from intracellular stores. There are fourteen kinds of mammalian phospholipase C proteins which are are classified into six isotypes (beta, gamma, delta, epsilon, zeta, eta). 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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