title: Magic angle spinning31P NMR spectroscopy reveals two essentially identical ionization states for the cardiolipin phosphates in phospholipid liposomes.
abstract: Specific membrane lipid composition is crucial for optimized structural and functional organization of biological membranes. Cardiolipin is a unique phospholipid and important component of the inner mitochondrial membrane. It is involved in energy metabolism, inner mitochondrial membrane transport, regulation of multiple metabolic reactions and apoptotic cell death. The physico-chemical properties of cardiolipin have been studied extensively but despite all these efforts there is still lingering controversy regarding the ionization of the two phosphate groups of cardiolipin. Results obtained in the 1990s and early 2000s suggested that cardiolipin has two disparate pKa values where one of the protons was proposed to be stabilized by an intramolecular hydrogen bond. This has led to extensive speculations on the roles of these two putative ionization states of cardiolipin in mitochondria. More recently the notion of two pKa values has been challenged and rejected by several groups. These studies relied on external measurements of proton adsorption or electrophoretic mobility of membranes but did not take into account the low pH phase behavior and chemical stability of cardiolipin. Here we used31P NMR to show that in the physiologically relevant membrane phospholipid environment, cardiolipin carries two negative charges at physiological pH. We additionally demonstrate the pH dependent phase behavior and chemical stability of cardiolipin containing membranes.
authors.affiliation: Department of Biological Sciences, Kent State University, Kent, OH, United States. Electronic address: ekooijma@kent.edu.
authors.forename: E E
authors.initials: EE
authors.lastname: Kooijman
authors.affiliation: Department of Biological Sciences, Kent State University, Kent, OH, United States.
authors.forename: L A
authors.initials: LA
authors.lastname: Swim
authors.affiliation: Department of Chemistry and Biochemistry, Kent State University, Kent, OH, United States.
authors.forename: Z T
authors.initials: ZT
authors.lastname: Graber
authors.affiliation: Department of Environmental and Occupational Health, University of Pittsburgh, Pittsburgh, PA, United States.
authors.forename: Y Y
authors.initials: YY
authors.lastname: Tyurina
authors.affiliation: Department of Critical Care Medicine, University of Pittsburgh, Pittsburgh, PA, United States.
authors.forename: H
authors.initials: H
authors.lastname: Bayır
authors.affiliation: Department of Environmental and Occupational Health, University of Pittsburgh, Pittsburgh, PA, United States.
authors.forename: V E
authors.initials: VE
authors.lastname: Kagan
mesh_terms: D002308:Cardiolipins / Q000737:chemistry*; D006860:Hydrogen Bonding; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008081:Liposomes / Q000737:chemistry*; D010710:Phosphates / Q000737:chemistry; D010713:Phosphatidylcholines / Q000737:chemistry*; D010714:Phosphatidylethanolamines / Q000737:chemistry*; D011522:Protons; D055672:Static Electricity
chemical_list: C519576:1,1',2,2'-tetraoleoylcardiolipin; D002308:Cardiolipins; D008081:Liposomes; D010710:Phosphates; D010713:Phosphatidylcholines; D010714:Phosphatidylethanolamines; D011522:Protons; C094877:dioleoyl phosphatidylethanolamine; C017251:1,2-oleoylphosphatidylcholine
keywords: Cardiolipin-protein interactions; Electron transport; Lipid ionization; Membrane electrostatics; Membrane structure; Mitochondria