EF-hand motif found in phosphoinositide phospholipase C beta 2 (PI-PLC-beta2)
PI-PLC-beta2, also termed 1-phosphatidylinositol 4,5-bisphosphate phosphodiesterase beta-2, or phospholipase C-beta-2 (PLC-beta2), is expressed at highest levels in cells of hematopoietic origin. It is activated by the heterotrimeric G protein alpha q subunits (G alpha(q)) through their C2 domain and long C-terminal extension. It is also activated by the beta-gamma subunits of heterotrimeric G proteins. PI-PLC-beta2 has two cellular binding partners, alpha- and gamma-synuclein. The binding of either alpha- and gamma-synuclein inhibits PI-PLC-beta2 activity through preventing the binding of its activator G alpha(q). However, the binding of gamma-synuclein to PI-PLC-beta2 does not affect its binding to G beta(gamma) subunits or small G proteins, but enhances these signals. Meanwhile, gamma-synuclein may protect PI-PLC-beta2 from protease degradation and contribute to its over-expression in breast cancer. In leukocytes, the G beta(gamma)-mediated activation of PI-PLC-beta2 can be promoted by a scaffolding protein WDR26, which is also required for the translocation of PI-PLC-beta2 from the cytosol to the membrane in polarized leukocytes. PI-PLC-beta2 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 C2 domain. Besides, it has a unique C-terminal coiled-coil (CT) domain necessary for homodimerization. The PLC catalytic core domain is a TIM barrel with two highly conserved regions (X and Y) split by a highly degenerate linker sequence.