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

Abstract

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 ~6 Å in pure TMCL, and increases AL from 64 Å2 (DMPC at 35°C) to 109 Å2 (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 2 Å for 20 mol% 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 = 40.8 Å2 for the ½TMCL gel phase, smaller than the DMPC gel phase with AL = 47.2 Å2, but similar to AL of DLPE = 41 Å2, consistent with untilted chains in gel phase TMCL.

Mechanical properties of lipid bilayers from molecular dynamics simulation

“…Otherwise, the NSE and x-ray results are close to each other, and lower than simulation. X-ray scattering of tetramyristoylcardiolipin (TMCL) at 323 K yielded K C = 7.5 ± 1.0 ×10 −20 J (Boscia et al, 2014) which is comparable with the x-ray determinations of K C for two-chained lipids.…”

Phosphatidylserine Stimulates Ceramide 1-Phosphate (C1P) Intermembrane Transfer by C1P Transfer Proteins

“…When anionic phosphoglycerides are added to the mix, their influence also needs consideration. Because PA shares the same small phosphate headgroup as C1P (58), minimal alteration of the C1P transbilayer distribution and the outer leaflet pool size is expected compared with C1P source vesicles lacking PA. By contrast, the PG headgroup volume is significantly larger than that of C1P and only slightly smaller than that of PC (59). Thus, the PG transbilayer distribution, like that of PC, tends to remain mass-distributed with ϳ65% in the outer leaflet of the donor vesicle bilayer (60).…”

Lipidomic and Ultrastructural Characterization of Cell Envelope ofStaphylococcus aureusGrown in the Presence of Human Serum

“…The CL enriched membrane was also thicker than wild type membrane and resisted daptomycin lipid extraction, membrane penetration and disruption (43). In bilayer model systems, inclusion of CL has been shown to lead to increased bilayer thickness and a stiffening of the membrane, which correlates with decreases susceptibility to membrane lysis induced by helical antimicrobial peptides (44, 45). Thus, increased content of CLs in S. aureus grown in a host environment could result in decreased susceptibility to daptomycin and other antimicrobial peptides.…”