Minimal Effect of Lipid Charge on Membrane Miscibility Phase Behavior in Three Ternary Systems

Giant unilamellar vesicles composed of a ternary mixture of phospholipids and cholesterol exhibit coexisting liquid phases over a range of temperatures and compositions. A significant fraction of lipids in biological membranes are charged. Here, we present phase diagrams of vesicles composed of phos...

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Bibliographic Details
Published in:Biophysical journal 2013-06, Vol.104 (12), p.2629-2638
Main Authors: Blosser, Matthew C., Starr, Jordan B., Turtle, Cameron W., Ashcraft, Jake, Keller, Sarah L.
Format: Article
Language:English
Subjects:
Biophysics
Cholesterol
Cholesterol - chemistry
Hot Temperature
lipid composition
Lipids
Mass spectrometry
Membrane
Membranes
phosphatidylcholines
Phosphatidylcholines - chemistry
Phosphatidylglycerols - chemistry
phosphatidylserines
physical phases
Static Electricity
temperature
Unilamellar Liposomes - chemistry
zwitterions
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Summary:Giant unilamellar vesicles composed of a ternary mixture of phospholipids and cholesterol exhibit coexisting liquid phases over a range of temperatures and compositions. A significant fraction of lipids in biological membranes are charged. Here, we present phase diagrams of vesicles composed of phosphatidylcholine (PC) lipids, which are zwitterionic; phosphatidylglycerol (PG) lipids, which are anionic; and cholesterol (Chol). Specifically, we use DiPhyPG-DPPC-Chol and DiPhyPC-DPPG-Chol. We show that miscibility in membranes containing charged PG lipids occurs over similarly high temperatures and broad lipid compositions as in corresponding membranes containing only uncharged lipids, and that the presence of salt has a minimal effect. We verified our results in two ways. First, we used mass spectrometry to ensure that charged PC/PG/Chol vesicles formed by gentle hydration have the same composition as the lipid stocks from which they are made. Second, we repeated the experiments by substituting phosphatidylserine for PG as the charged lipid and observed similar phenomena. Our results consistently support the view that monovalent charged lipids have only a minimal effect on lipid miscibility phase behavior in our system.
ISSN:0006-3495
1542-0086
DOI:10.1016/j.bpj.2013.04.055