title: Ca(2+) induces PI(4,5)P2 clusters on lipid bilayers at physiological PI(4,5)P2 and Ca(2+) concentrations.
abstract: Calcium has been shown to induce clustering of PI(4,5)P2 at high and non-physiological concentrations of both the divalent ion and the phosphatidylinositol, or on supported lipid monolayers. In lipid bilayers at physiological conditions, clusters are not detected through microscopic techniques. Here, we aimed to determine through spectroscopic methodologies if calcium plays a role in PI(4,5)P2 lateral distribution on lipid bilayers under physiological conditions. Using several different approaches which included information on fluorescence quantum yield, polarization, spectra and diffusion properties of a fluorescent derivative of PI(4,5)P2 (TopFluor(TF)-PI(4,5)P2), we show that Ca(2+) promotes PI(4,5)P2 clustering in lipid bilayers at physiological concentrations of both Ca(2+) and PI(4,5)P2. Fluorescence depolarization data of TF-PI(4,5)P2 in the presence of calcium suggests that under physiological concentrations of PI(4,5)P2 and calcium, the average cluster size comprises ~15 PI(4,5)P2 molecules. The presence of Ca(2+)-induced PI(4,5)P2 clusters is supported by FCS data. Additionally, calcium mediated PI(4,5)P2 clustering was more pronounced in liquid ordered (lo) membranes, and the PI(4,5)P2-Ca(2+) clusters presented an increased affinity for lo domains. In this way, PI(4,5)P2 could function as a lipid calcium sensor and the increased efficiency of calcium-mediated PI(4,5)P2 clustering on lo domains might provide targeted nucleation sites for PI(4,5)P2 clusters upon calcium stimulus.
authors: Centro de Química-Física Molecular and Institute of Nanoscience and Nanotechnology, Instituto Superior Técnico, University of Lisbon, Lisbon, Portugal.
authors: Maria J
authors: MJ
authors: Sarmento
authors: Centro de Química-Física Molecular and Institute of Nanoscience and Nanotechnology, Instituto Superior Técnico, University of Lisbon, Lisbon, Portugal; Departamento de Química e Bioquímica, FCUL, University of Lisbon, Lisbon, Portugal.
authors: Ana
authors: A
authors: Coutinho
authors: Centro de Química-Física Molecular and Institute of Nanoscience and Nanotechnology, Instituto Superior Técnico, University of Lisbon, Lisbon, Portugal.
authors: Aleksander
authors: A
authors: Fedorov
authors: Centro de Química-Física Molecular and Institute of Nanoscience and Nanotechnology, Instituto Superior Técnico, University of Lisbon, Lisbon, Portugal.
authors: Manuel
authors: M
authors: Prieto
authors: Centro de Química-Física Molecular and Institute of Nanoscience and Nanotechnology, Instituto Superior Técnico, University of Lisbon, Lisbon, Portugal. Electronic address: fernandesf@ist.utl.pt.
authors: Fabio
authors: F
authors: Fernandes
mesh_terms: D002118:Calcium / Q000494:pharmacology*; D002462:Cell Membrane / Q000378:metabolism*; D006801:Humans; D008051:Lipid Bilayers / Q000378:metabolism*; D008081:Liposomes; D008560:Membrane Fluidity / Q000187:drug effects*; D019269:Phosphatidylinositol 4,5-Diphosphate / Q000378:metabolism*; D013050:Spectrometry, Fluorescence
chemical_list: D008051:Lipid Bilayers; D008081:Liposomes; D019269:Phosphatidylinositol 4,5-Diphosphate; D002118:Calcium
keywords: Calcium; FCS; FRET; Fluorescence spectroscopy; PI(4,5)P(2)