The effect of fusion inhibitors on the phase behaviour of N-methylated dioleoylphosphatidylethanolamine

An Evidence for a Novel Antiviral Mechanism: Modulating Effects of Arg-Glc Maillard Reaction Products on the Phase Transition of Multilamellar Vesicles

Maillard reaction products (MRPs) of protein, amino acids, and reducing sugars from many foods and aqueous extracts of herbs are found to have various bioactivities, including antiviral effects. A hypothesis was proposed that their antiviral activity is due to the interaction with the cellular membrane. Aiming to estimate the possible actions of MRPs on phospholipid bilayers, the Arg-Glc MRPs were prepared by boiling the pre-mixed solution of arginine and glucose for 60 min at 100°C and then examined at a series of concentrations for their effects on the phase transition of MeDOPE multilamellar vesicles (MLVs), for the first time, by using differential scanning calorimetry (DSC) and temperature-resolved small-angle X-ray scattering (SAXS). Arg-Glc MRPs inhibited the lamellar gel–liquid crystal (L_β-L_α), lamellar liquid crystal–cubic (L_α-Q_II), and lamellar liquid crystal–inverted hexagonal (L_α-H_II) phase transitions at low concentration (molar ratio of lipid vs. MRPs was 100:1 or 100:2), but promoted all three transitions at medium concentration (100:5). At high concentration (10:1), the MRPs exhibited inhibitory effect again. The fusion peptide from simian immunodeficiency virus (SIV) induces membrane fusion by promoting the formation of a non-lamellar phase, e.g., cubic (Q_II) phase, and inhibiting the transition to H_II. Arg-Glc MRPs, at low concentration, stabilized the lamellar structure of SIV peptide containing lipid bilayers, but facilitated the formation of non-lamellar phases at medium concentration (100:5). The concentration-dependent activity of MRPs upon lipid phase transition indiciates a potential role in modulating some membrane-related biological events, e.g., viral membrane fusion.

Neutron diffraction with an excess-water cell

As part of a study of the molecular basis of membrane fusion by enveloped viruses, we have used neutron diffraction to study the lamellar (L(α)) to inverse hexagonal (H(II)) phase transition in the phospholipid N-methylated dioleoylphosphatidylethanolamine. This lipid was chosen because its phase transitions are particularly sensitive to the presence of agents that have been demonstrated to promote or inhibit membrane fusion. Two different geometries of neutron diffraction were used: small angle scattering (SANS) and a membrane diffractometer. The SANS measurements were carried out on the SWAN instrument at KEK, Japan, using dispersions of multilamellar vesicles (MLVs). The diffractometer measurements used the V1 instrument at BeNSC-HMI, Germany, with a specially-constructed cell that holds a stack of lipid bilayers in an excess-water state. The two approaches are compared and discussed. Although the diffractometer takes considerably longer to collect the data, it records much higher resolution than the SANS instrument. The samples recorded in the excess-water cell were shown to be well aligned, despite the lipids being fully hydrated, allowing for the production of high-resolution data. Trial measurements performed have demonstrated that sample alignment is preserved throughout the L(α) to H(II) phase transition, thereby opening up possibilities for obtaining high-resolution data from non-lamellar phases.

The kinetics of non-lamellar phase formation in DOPE-Me: relevance to biomembrane fusion

The mechanism of the lamellar/inverted cubic (QII) phase transition is related to that of membrane fusion in lipid systems. N-Monomethylated dioleoylphosphatidylethanolamine (DOPE-Me) exhibits this transition and is commonly used to investigate the effects of exogenous substances, such as viral fusion peptides, on the mechanism of membrane fusion. We studied DOPE-Me phase behavior as a first step in evaluating the effects of membrane-spanning peptides on inverted phase formation and membrane fusion. These measurements show that: a) the onset temperatures for QII and inverted hexagonal (HII) phase formation both are temperature scan rate-dependent; b) longer pre-incubation times at low temperature and lower temperature scan rates favor formation of the QII phase; and c) in temperature-jump experiments between 61 and 65 degrees C, the meta-stable HII phase forms initially, and disappears slowly while the QII phase develops. These observations are rationalized in the context of a mechanism for both the lamellar/non-lamellar phase transition and the related process of membrane fusion.

The fusion peptide of simian immunodeficiency virus and the phase behaviour of N-methylated dioleoylphosphatidylethanolamine

Temperature-scan X-ray scattering was used to study the effect of the fusion peptide of simian immunodeficiency virus (SIV) on the lipid polymorphism of N-methylated dioleoylphosphatidylethanolamine (DOPE-Me), in the presence and absence of one or both of the fusion inhibitors carbobenzoxy-D-phenylalanine-L-phenylalanine-glycine and 1-lauroyl-2-hydroxy-sn-glycero-3-phosphocholine (LPC). Using X-ray diffraction at stations 2.1 and 8.2 of the Synchrotron Radiation Source at Daresbury Laboratory, UK, the structure of multilamellar vesicles (MLVs) was probed as the temperature was raised from 20 to 90 degrees C. The results are compared to those of similar studies, reported earlier, that used the fusion peptide of feline leukaemia virus (FeLV) which, at 28 amino acid residues in length, is considerably longer than the SIV peptide (12 amino acid residues). We interpret the results within the framework of current understanding of membrane fusion, and demonstrate how observed lipid polymorphism might describe the fusion process.