EF-hand motif found in phospholipase C-related but catalytically inactive protein 1 (PRIP-1)
PRIP-1, also termed phospholipase C-deleted in lung carcinoma, or inactive phospholipase C-like protein 1 (PLC-L1), or p130, is a novel inositol 1,4,5-trisphosphate (InsP3) binding protein that is predominantly expressed in the brain. It is involved in InsP3-mediated calcium signaling pathway and GABA(A)receptor-mediated signaling pathway. It interacts with the catalytic subunits of protein phosphatase 1 (PP1) and protein phosphatase 2A (PP2A), and functions as a scaffold to regulate the activities and subcellular localizations of both PP1 and PP2A in phospho-dependent cellular signaling. It also promotes the translocation of phosphatases to lipid droplets to trigger the dephosphorylation of hormone-sensitive lipase (HSL) and perilipin A, thus reducing protein kinase A (PKA)-mediated lipolysis. Moreover, PRIP-1 plays an important role in insulin granule exocytosis through the association with GABAA-receptor-associated protein (GABARAP) to form a complex to regulate KIF5B-mediated insulin secretion. It also inhibits regulated exocytosis through direct interactions with syntaxin 1 and synaptosomal-associated protein 25 (SNAP-25) via its C2 domain. Furthermore, PRIP-1 has been implicated in the negative regulation of bone formation. PRIP-1 has a primary structure and domain architecture, incorporating a pleckstrin homology (PH) domain, four atypical EF-hand motifs, a PLC catalytic core domain with highly conserved X- and Y-regions split by a linker sequence, and a C-terminal C2 domain, similar to phosphoinositide-specific phospholipases C (PI-PLC, EC 22.214.171.124)-delta isoforms. Due to replacement of critical catalytic residues, PRIP-1 does not have PLC enzymatic activity.