Short-chain lecithin long-chain phospholipid unilamellar vesicles: asymmetry, dynamics, and enzymatic hydrolysis of the short-chain component

Abstract

Asymmetric unilamellar vesicles are produced when short-chain phospholipids (fatty acyl chain lengths of 6-8 carbons) are mixed with long-chain phospholipids (fatty acyl chain lengths of 14 carbons or longer) in ratios of 1:4 short-chain/long-chain component. Short-chain lecithins are preferentially distributed on the outer monolayer, while a short-chain phosphatidylethanolamine derivative appears to localize on the inner monolayer of these spontaneously forming vesicles. Lanthanide NMR shift experiments clearly show a difference in head-group/ion interactions between the short-chain and long-chain species. Two-dimensional 1H NMR studies reveal efficient spin diffusion networks for the short-chain species embedded in the long-chain bilayer matrix. The short-chain lecithin is considerably more mobile than the long-chain component but has hindered motion compared to short-chain lecithin micelles. This differentiation in physical characteristics of the two phospholipid components is critical to understanding the activity of phospholipases toward these binary systems.

1H–13C INEPT MAS NMR correlation experiments with 1H–1H mediated magnetization exchange to probe organization in lipid biomembranes

“…For the 1 H-13 C correlation experiments presented in this paper, two different methods for 1 H-1 H magnetization exchange during the mixing time (s mix ) were investigated. In one set of experiments no additional 1 H rf pulses were introduced during s mix such that the observed 1 H-1 H magnetization exchange occurs via NOE type dipolar relaxation analogous with the 1 H NOESY MAS NMR experiments previously reported [13,14,17,19,20]. In the second set of experiments the 1 H-1 H magnetization exchange occur via scaled 1 H-1 H dipolar interactions reintroduced using the radio-frequency dipolar recoupling (RFDR) pulse sequence on the 1 H channel during s mix .…”

“…These observations prompted a series of two-dimensional (2D) 1 H NOESY MAS NMR experiments that allowed molecular contacts between different lipid regions, as well as between lipids and other constituents within the membrane to be determined [13][14][15][16][17][18]. The observation of contacts between the methyl protons in lipid headgroup and the protons of the terminal methyl in the alkyl chain lead to extensive discussion into the relative impact of spin diffusion and intermolecular dipolar interactions resulting from lipid disorder on the observed cross-relaxation in 1 H NOESY MAS NMR experiments [13,14,17,19,20]. More recently, the selectivity and sensitivity of 1 H MAS NMR has been improved by use of pulsed field gradients (PFG) [2].…”

Tools for characterizing biomembranes : final LDRD report.

“…These observations prompted a series of twodimensional (2D) 1 H NOESY MAS NMR experiments that allowed molecular contacts between different lipid regions, as well as between lipids and other constituents within the membrane to be determined [51][52][53][54][55][56]. The observation of contacts between the methyl protons in lipid headgroup and the protons of the terminal methyl in the alkyl chain lead to extensive discussion into the relative impact of spin diffusion and intermolecular dipolar interactions resulting from lipid disorder on the observed crossrelaxation in 1 H NOESY MAS NMR experiments [51,52,55,57,58]. More recently, the selectivity and sensitivity of 1 H MAS NMR has been improved by use of pulsed field gradients (PFG) [40].…”

Interfacial Enzyme Kinetics at the Phospholipid/ Water Interface: Practical Considerations

“…Mixtures of short-chain and long-chain phospholipids also form SLUVs (14,16,37). These are small unilamellar vesicles that are roughly the same size and structure as sonicated SUVs with the exception that the short-chain phospholipids are located only in the outer leaflet of the bilayer.…”

“…These structures are also formed spontaneously when the two types of phospholipid are mixed. It was found that at least two phospholipases, cobra venom PLA 2 and phospholipase C, preferentially hydrolyze the short-chain phospholipids at a rate that is equivalent to that of micelles and about 20-fold higher than the rate on the long-chain phospholipid dispersed in sonicated SUVs (37). These mixtures of short-and long-chain phospholipids can also form mixed micelles.…”