Structure of vitaminylated lipids in aqueous dispersion: X-ray diffraction and phosphorus-31 NMR studies of N-biotinylphosphatidylethanolamines

Abstract

The structures of the phases formed in excess buffer (at pH 7.4) by a homologous series of saturated diacylphosphatidylethanolamines in which the headgroup is N-derivatized with biotin have been investigated for chain lengths of C(12:0) to C(20:0), using both 31P nuclear magnetic resonance (NMR) spectroscopy and small-angle X-ray diffraction. In 1 M NaCl, all lipids display 31P NMR spectra characteristic of a lamellar gel phase at low temperature. In the fluid phase, the lipids of C(12:0) and C(14:0) chain lengths display isotropic 31P NMR spectra, corresponding to aggregated phases with high surface curvature, whereas those with C(18:0) and C(20:0) chain lengths display sharp axial powder patterns characteristic of a lamellar (L alpha) phase. The lipid of intermediate C(16:0) chain length displays a more complex temperature dependence of the 31P NMR spectra in the fluid phase. The spectra convert from an axial powder pattern of unusually low chemical shift anisotropy to one characteristic of a fluid lamellar (L alpha) phase with increasing temperature. The small-angle X-ray diffraction patterns of the lipids in 1 M NaCl have lamellar repeat spacings in the gel phase which increase linearly with chain length and are consistently lower than those in the fluid phase [for chain lengths of C(16:0) to C(20:0)]. In addition, the gradient in long spacing with chain length in the gel phase is approximately half that expected for a gel phase with untilted, all-trans chains, indicating that the lipid chains are interdigitated in the gel phase (L beta i).(ABSTRACT TRUNCATED AT 250 WORDS)

Differential scanning calorimetry of thermotropic phase transitions in vitaminylated lipids: aqueous dispersions of N-biotinyl phosphatidylethanolamines

“…Additionally, comparison is made between the transition temperatures of the biotin-PEs in the presence and absence of salt, in order to reveal the effects of surface electrostatics in the latter case. In this analysis, the different structures of the lyotropic phases of the biotin-PEs are to be borne in mind, in particular that the gel phases are interdigitated and the fluid phases in the absence of salt are micellar (Swamy et al, 1993). Thus both the chain packing and the surface area per lipid headgroup of the biotin-PEs can differ from those found with normal lamellar phospholipid phases.…”

“…No other thermotropic transitions than those shown were detected over the range -20°to +80°C for DLBPE, 20 to 60°C for DMBPE, 50 to 85°C for DPBPE, 100 to 70°C for DSBPE, and 20°to 90°C for DABPE. In particular, no calorimetric endo-/exotherm was detected corresponding to the structural transition from the IM, to the La phase that takes place with DPBPE dispersions in 1 M NaCl over the temperature range from 600 to 70°C (Swamy et al, 1993). The transition temperatures, transition enthalpies, and transition entropies obtained from heating scans for the biotin-PEs of different chainlengths in 1 M NaCl, 10 mM Hepes, 1 mM EDTA, pH 7.4, are given in Table 1.…”

“…Whereas this value is comparable to that expected for the chain-melting phase transition of a normal lipid bilayer (cf. Marsh, 1990), it is surprisingly large for the biotin-PE system where the lipid chains are interdigitated in the gel phase (Swamy et al, 1993), even though the fluid phase in the absence of salt is micellar and therefore possesses a considerably more open headgroup structure. Possibly effects other than electrostatic interactions contribute also to the decrease of the phase tran-sition temperature in the absence of salt.…”

“…The biotin-PEs are interesting also from the point of view of phospholipid model membranes, because the stable phases of their aqueous dispersions differ in many instances from those normally encountered with the common diacyl phospholipid species (Swamy et al, 1993). They form interdigitated lamellar gel phases (Li) and, for the shorter chainlengths (C(12:0) and C(14:0)) in the presence of salt, they form novel nonlamellar fluid phases of an isotropic type (IM1) that consist of aggregated normal micelles.…”

Spin-Label Electron Spin Resonance Studies on the Dynamics of the Different Phases of N-Biotinylphosphatidylethanolamines

“…In this context, it is therefore important to study the behavior of the different phases formed by the various biotinylated phospholipids in aqueous dispersion. In order to characterize the polymorphic phase behavior of these lipids, studies have been made previously on a homologous series of diacyl-Abiotinylphosphatidylethanolamines (biotin-PEs)1 with chain lengths from C( 12:0) to C(20:0) by using differential scanning calorimetry, 31P-NMR spectroscopy and low-angle X-ray diffraction (Swamy et al, 1993(Swamy et al, ,1994. It was found that, in 1 Abbreviations: ESR, electron spin resonance; NMR, nuclear magnetic resonance; DSC, differential scanning calorimetry; PC, phosphatidylcholine; PE, phosphatidylethanolamine; biotin-PE, IV-biotinylphosphatidylethanolamine; DLBPE, DMBPE, DPBPE, DSBPE, and and l, the main, the various biotin-PE dispersions exhibited unusual phases, other than the lamellar gel and fluid phases that are found normally with long-chain diacyl phospholipids.…”