Clustering of syntaxin-1A in model membranes is modulated by phosphatidylinositol 4,5-bisphosphate and cholesterol.
Syntaxin-1A is part of the SNARE complex that forms in membrane fusion in neuronal exocytosis of synaptic vesicles. Together with SNAP-25 the single-span transmembrane protein syntaxin-1A forms the receptor complex on the plasma membrane of neuroendocrine cells. Previous studies have shown that syntaxin-1A occurs in clusters that are different from lipid rafts in neuroendocrine plasma membranes. However, the interactions that promote these clusters have been largely unexplored. Here, we have reconstituted syntaxin-1A into lipid model membranes, and we show that syntaxin cluster formation depends on cholesterol in a lipid system that lacks sphingomyelin and therefore does not form liquid-ordered phases that are commonly believed to represent lipid rafts in cell membranes. Rather, the cholesterol-induced clustering of syntaxin is found to be reversed by as little as 1-5 mol % of the regulatory lipid phosphatidylinositol 4,5-bisphosphate (PI-4,5-P(2)), and PI-4,5-P(2) is shown to bind electrostatically to syntaxin, presumably mediated by the highly positively charged juxtamembrane domain of syntaxin. Possible implications of these results to the regulation of SNARE-mediated membrane fusion are discussed.
Center for Membrane Biology and Department of Molecular Physiology and Biological Physics, University of Virginia, Charlottesville, Virginia 22908, USA.
David H
DH
Murray
Lukas K
LK
Tamm
D000818:Animals; D002462:Cell Membrane / Q000737:chemistry* / Q000378:metabolism*; D002784:Cholesterol / Q000378:metabolism*; D031541:Fluorescence Resonance Energy Transfer; D006863:Hydrogen-Ion Concentration; D008051:Lipid Bilayers / Q000737:chemistry / Q000378:metabolism; D019269:Phosphatidylinositol 4,5-Diphosphate / Q000378:metabolism*; D011485:Protein Binding; D051381:Rats; D050827:Syntaxin 1 / Q000378:metabolism*
D008051:Lipid Bilayers; D019269:Phosphatidylinositol 4,5-Diphosphate; D050827:Syntaxin 1; D002784:Cholesterol