EF-hand motif found in metazoan phosphoinositide-specific phospholipase C (PI-PLC)-beta isozymes
PI-PLC-beta isozymes represent a class of metazoan PI-PLCs that hydrolyze the membrane lipid phosphatidylinositol 4,5-bisphosphate (PIP2) to propagate diverse intracellular responses that underlie the physiological action of many hormones, neurotransmitters, and growth factors (EC 184.108.40.206). They have been implicated in numerous processes relevant to central nervous system (CNS), including chemotaxis, cardiovascular function, neuronal signaling, and opioid sensitivity. Like other PI-PLC isozymes, PI-PLC-beta isozymes contain 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, they have 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. There are four PI-PLC-beta isozymes (1-4). PI-PLC-beta1 and PI-PLC-beta3 are expressed in a wide range of tissues and cell types, whereas PI-PLC-beta2 and PI-PLC-beta4 have been found only in hematopoietic and neuronal tissues, respectively. All PI-PLC-beta isozymes are activated by the heterotrimeric G protein alpha subunits of the Gq class through their C2 domain and long C-terminal extension. They are GTPase-activating proteins (GAPs) for these G alpha(q) proteins. PI-PLC-beta2 and PI-PLC-beta3 can also be activated by beta-gamma subunits of the G alpha(i/o) family of heterotrimeric G proteins and the small GTPases such as Rac and Cdc42. This family also includes two invertebrate homologs of PI-PLC-beta, PLC21 from cephalopod retina and No receptor potential A protein (NorpA) from Drosophila melanogaster.