X-ray structure, thermodynamics, elastic properties and MD simulations of cardiolipin/dimyristoylphosphatidylcholine mixed membranes

•Structures of pure gel and fluid TMCL are obtained using X-ray scattering.•Fluid phase TMCL thickens DMPC bilayers and orders bilayer chains.•AL of pure TMCL at 50°C is 109Å2 and DHH is 38.6Å, using volumes and SDP fitting.•Bending modulus, KC, increases with increasing TMCL, indicating bilayer sti...

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Published in:Chemistry and physics of lipids 2014-02, Vol.178, p.1-10
Main Authors: Boscia, Alexander L., Treece, Bradley W., Mohammadyani, Dariush, Klein-Seetharaman, Judith, Braun, Anthony R., Wassenaar, Tsjerk A., Klösgen, Beate, Tristram-Nagle, Stephanie
Format: Article
Language:English
Subjects:
Calorimetry, Differential Scanning
Cardiolipins - chemistry
Crystallography, X-Ray
Differential scanning calorimetry
Dimyristoylphosphatidylcholine - chemistry
Dimyristoylphosphatidylcholine - metabolism
DMPC
Gels - chemistry
LAXS
Lipid bilayer structure
Lipid Bilayers - chemistry
Lipid Bilayers - metabolism
Molecular Conformation
Molecular Dynamics Simulation
Thermodynamics
Transition Temperature
WAXS
X-ray diffuse scattering
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Summary:•Structures of pure gel and fluid TMCL are obtained using X-ray scattering.•Fluid phase TMCL thickens DMPC bilayers and orders bilayer chains.•AL of pure TMCL at 50°C is 109Å2 and DHH is 38.6Å, using volumes and SDP fitting.•Bending modulus, KC, increases with increasing TMCL, indicating bilayer stiffening.•AL of pure gel phase TMCL at 35°C is 81.5Å2 and DHH is 42.6Å. Cardiolipins (CLs) are important biologically for their unique role in biomembranes that couple phosphorylation and electron transport like bacterial plasma membranes, chromatophores, chloroplasts and mitochondria. CLs are often tightly coupled to proteins involved in oxidative phosphorylation. The first step in understanding the interaction of CL with proteins is to obtain the pure CL structure, and the structure of mixtures of CL with other lipids. In this work we use a variety of techniques to characterize the fluid phase structure, material properties and thermodynamics of mixtures of dimyristoylphosphatidylcholine (DMPC) with tetramyristoylcardiolipin (TMCL), both with 14-carbon chains, at several mole percentages. X-ray diffuse scattering was used to determine structure, including bilayer thickness and area/lipid, the bending modulus, KC, and SXray, a measure of chain orientational order. Our results reveal that TMCL thickens DMPC bilayers at all mole percentages, with a total increase of ∼6Å in pure TMCL, and increases AL from 64Å2 (DMPC at 35°C) to 109Å2 (TMCL at 50°C). KC increases by ∼50%, indicating that TMCL stiffens DMPC membranes. TMCL also orders DMPC chains by a factor of ∼2 for pure TMCL. Coarse grain molecular dynamics simulations confirm the experimental thickening of 2Å for 20mol% TMCL and locate the TMCL headgroups near the glycerol-carbonyl region of DMPC; i.e., they are sequestered below the DMPC phosphocholine headgroup. Our results suggest that TMCL plays a role similar to cholesterol in that it thickens and stiffens DMPC membranes, orders chains, and is positioned under the umbrella of the PC headgroup. CL may be necessary for hydrophobic matching to inner mitochondrial membrane proteins. Differential scanning calorimetry, SXray and CGMD simulations all suggest that TMCL does not form domains within the DMPC bilayers. We also determined the gel phase structure of TMCL, which surprisingly displays diffuse X-ray scattering, like a fluid phase lipid. AL=40.8Å2 for the ½TMCL gel phase, smaller than the DMPC gel phase with AL=47.2Å2, but similar to AL of DLPE=41Å2, consis
ISSN:0009-3084
1873-2941
DOI:10.1016/j.chemphyslip.2013.12.010