title: NAADP binding to its target protein in sea urchin eggs requires phospholipids.
abstract: Mobilization of intracellular Ca2+ pools by NAADP (nicotinic acid-adenine dinucleotide phosphate) is becoming increasingly recognized as an important determinant of complex Ca2+ signals. However, the properties of the putative Ca2+ channel activated by NAADP are poorly defined. In the present study, we provide evidence that binding of NAADP to its target protein in sea urchin eggs requires phospholipids. Decreasing the level of protein-bound lipid in detergent extracts by either dilution of the preparation at a fixed detergent concentration or increasing the detergent concentration at a fixed protein concentration inhibited [32P]NAADP binding. These effects were prevented by the addition of phospholipids, but not other related molecules, were reversible and were associated with a marked decrease in the apparent affinity of the target protein for its ligand. Additionally, we show that the extent of dissociation of NAADP-receptor ligand complexes during gel filtration in the presence of detergent correlates well with the extent of delipidation. Our data highlight the importance of the lipid environment for interaction of NAADP with its target protein.
authors.affiliation: The Old Squash Courts, Department of Physiology, University College London, Gower Street, London WC1E 6BT, UK.
authors.forename: Dev
authors.initials: D
authors.lastname: Churamani
authors.forename: George D
authors.initials: GD
authors.lastname: Dickinson
authors.forename: Sandip
authors.initials: S
authors.lastname: Patel
mesh_terms: D000818:Animals; D002417:Cattle; D002457:Cell Extracts / Q000737:chemistry; D002850:Chromatography, Gel; D003902:Detergents / Q000494:pharmacology; D004527:Egg Proteins / Q000378:metabolism*; D008024:Ligands; D009249:NADP / Q000031:analogs & derivatives* / Q000378:metabolism; D017830:Octoxynol / Q000494:pharmacology; D010063:Ovum / Q000378:metabolism*; D010743:Phospholipids / Q000302:isolation & purification / Q000378:metabolism / Q000494:pharmacology*; D011485:Protein Binding / Q000187:drug effects; D011869:Radioligand Assay; D012617:Sea Urchins / Q000166:cytology*; D012995:Solubility; D013379:Substrate Specificity / Q000187:drug effects
chemical_list: D002457:Cell Extracts; D003902:Detergents; D004527:Egg Proteins; D008024:Ligands; D010743:Phospholipids; D009249:NADP; C024376:NAADP; D017830:Octoxynol