title: Fluorescence studies suggest a role for alpha-synuclein in the phosphatidylinositol lipid signaling pathway.
abstract: Alpha-synuclein plays a key role in the pathogenesis of many neurodegenerative diseases. To date, its cellular role has yet to be determined, although it has been proposed to be connected to calcium and G protein-mediated dopamine signaling. Alpha-synuclein is known to bind strongly to model membrane surfaces where it may interact with other membrane-associated proteins. Here, we find that the membrane association of alpha-synuclein is enhanced by the presence of phosphatidylinositol 4,5-bisphosphate [PI(4,5)P(2)] and Ca(2+). We also find that alpha-synuclein interacts with high affinity with the G protein-regulated enzyme phospholipase Cbeta(2) (PLCbeta(2)), which catalyzes the hydrolysis of PI(4,5)P(2). Binding of alpha-synuclein to PLCbeta(2) reduces its catalytic activity by 50%, but causes its level of activation by Gbetagamma subunits to increase from 4- to 24-fold. This effect is greatly reduced for A53T alpha-synuclein, which is a mutant associated with familial Parkinson's disease. PI(4,5)P(2) hydrolysis by PLCbeta(2) results in an increase in the intracellular Ca(2+) concentration, and we find that in cultured cells the presence of alpha-synuclein results in a 6-fold enhancement in the release of Ca(2+) from intracellular stores in response to agents that release Gbetagamma subunits relative to controls. Alpha-synuclein also enhances the increase in the level of inositol phosphates seen upon G protein stimulation, suggesting that it also may interact with PLCbeta(2) in cells. Given that Ca(2+) and dopamine regulation are mediated through PLCbeta and G protein signals, our results suggest that alpha-synuclein may play a role in inositol phospholipid signaling.
authors.affiliation: Department of Physiology and Biophysics, State University of New York, Stony Brook, New York 11794-8661, USA.
authors.forename: Vijaya
authors.initials: V
authors.lastname: Narayanan
authors.forename: Yuanjian
authors.initials: Y
authors.lastname: Guo
authors.forename: Suzanne
authors.initials: S
authors.lastname: Scarlata
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D020013:Calcium Signaling / Q000235:genetics; D002460:Cell Line; D004298:Dopamine / Q000737:chemistry; D044387:GTP-Binding Protein beta Subunits / Q000737:chemistry; D044388:GTP-Binding Protein gamma Subunits / Q000737:chemistry; D006801:Humans; D007295:Inositol Phosphates / Q000096:biosynthesis; D007527:Isoenzymes / Q000737:chemistry / Q000378:metabolism; D008051:Lipid Bilayers / Q000378:metabolism; D018613:Microscopy, Confocal; D008856:Microscopy, Fluorescence; D009419:Nerve Tissue Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D019269:Phosphatidylinositol 4,5-Diphosphate / Q000378:metabolism; D010716:Phosphatidylinositols / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D054799:Phospholipase C beta; D011485:Protein Binding; D051381:Rats; D013050:Spectrometry, Fluorescence; D051843:Synucleins; D010738:Type C Phospholipases / Q000737:chemistry / Q000378:metabolism; D015854:Up-Regulation / Q000235:genetics; D051844:alpha-Synuclein
chemical_list: C118981:G-protein Beta gamma; D044387:GTP-Binding Protein beta Subunits; D044388:GTP-Binding Protein gamma Subunits; D007295:Inositol Phosphates; D007527:Isoenzymes; D008051:Lipid Bilayers; D009419:Nerve Tissue Proteins; D019269:Phosphatidylinositol 4,5-Diphosphate; D010716:Phosphatidylinositols; C497604:SNCA protein, human; C497606:Snca protein, rat; D051843:Synucleins; D051844:alpha-Synuclein; D010738:Type C Phospholipases; D054799:Phospholipase C beta; D002118:Calcium; D004298:Dopamine