EF-hand motif found in phosphoinositide phospholipase C delta 1 (PI-PLC-delta1)
PI-PLC-delta1, also termed 1-phosphatidylinositol 4,5-bisphosphate phosphodiesterase delta-1 (PLCD1), or phospholipase C-III (PLC-III), or phospholipase C-delta-1 (PLC-delta-1), is present in high abundancy in the brain, heart, lung, skeletal muscle and testis. It is activated by high calcium levels generated by other PI-PLC family members, and therefore functions as a calcium amplifier within the cell. PI-PLC-delta1 is required for maintenance of homeostasis in skin and metabolic tissues. Moreover, it is essential in trophoblasts for placental development. Simultaneous loss of PI-PLC-delta1 may cause placental vascular defects, leading to embryonic lethality. PI-PLC-delta1 can be positively or negatively regulated by several binding partners, including p122/Rho GTPase activating protein (RhoGAP), Gha/Transglutaminase II, RalA, and calmodulin. It is involved in Alzheimer's disease and hypertension. Furthermore, PI-PLC-delta1 regulates cell proliferation and cell-cycle progression from G1- to S-phase by control of cyclin E-CDK2 activity and p27 levels. It can be activated by alpha1-adrenoreceptors (AR) in a calcium-dependent manner and may be important for G protein-coupled receptors (GPCR) responses in vascular smooth muscle (VSM). PI-PLC-delta1 may also be involved in noradrenaline (NA)-induced phosphatidylinositol-4,5-bisphosphate (PIP2) hydrolysis and modulate sustained contraction of mesenteric small arteries. In addition, it inhibits thermogenesis and induces lipid accumulation, and therefore contributes to the development of obesity. PI-PLC-delta1 contains a core set of domains, including an N-terminal pleckstrin homology (PH) domain, four atypical EF-hand motifs, a PLC catalytic core, and a single C-terminal C2 domain. The PLC catalytic core domain is a TIM barrel with two highly conserved regions (X and Y) split by a highly degenerate linker sequence. PI-PLC-delta1 can regulate the binding of PH domain to PIP2 in a Ca2+-dependent manner through its functionally important EF-hand domains. In addition, PI-PLC-delta1 possesses a classical leucine-rich nuclear export sequence (NES) located in the EF hand motifs, as well as a nuclear localization signal within its linker region, both of which may be responsible for translocating PI-PLC-delta1 into and out of the cell nucleus.