Influence of antimicrobial peptides on the formation of nonlamellar lipid mesophases.

We have studied the influence of four antimicrobial peptides of different secondary and ternary structure--melittin (Mel), protegrin-1 (PG-1), peptidyl-glycylleucine-carboxyamide (PGLa), and gramicidin S (GS)--on the lamellar-to-nonlamellar transition of palmitoyloleoyl phosphatidylethanolamine (POPE) applying differential scanning calorimetry and small-angle X-ray diffraction. None of the peptides studied led to the formation of an inverted hexagonal phase observed for pure POPE at high temperatures. Instead either cubic or lamellar phases were stabilized to different degrees.

Effects of non-ionic surfactants N-alkyl-N,N-dimethylamine-N-oxides on the structure of a phospholipid bilayer: small-angle X-ray diffraction study.

Effects of non-ionic surfactants N-alkyl-N,N-dimethylamine-N-oxides (C(n)NO, n is the number of alkyl carbons) on the structure of egg yolk phosphatidylcholine (EYPC) bilayers in the lamellar fluid phase was studied by small-angle X-ray diffraction as a function of H(2)O:EYPC and C(n)NO:EYPC molar ratios. The bilayer thickness d(L) and the lipid surface area at the bilayer-aqueous interface S(L) were calculated from the repeat period, d of the lamellar phase, based on the model that water and EYPC + CnNO molecules form separated layers and that their molecular volumes are additive. In the studied range of m=CnNO:EYPC molar ratios up to 1:1, d(L) and S(L) change linearly.

X-ray diffraction and neutron scattering studies of amphiphile-lipid bilayer organization.

The lipid bilayer thickness d(L), the transbilayer distance of lipid phosphate groups d(pp/inf> and the lipid surface area A(L) of fluid hydrated bilayers of lamellar phases of egg phosphatidylcholine or dipalmitoylphosphatidylcholine containing N-alkyl-N,N-dimethylamine N-oxides (CnNO), 1,4-butanedi-ammonium-N,N'-dialkyl-N,N,N',N'-tetramethyl dibromides (GSn) or mono-hydrochlorides of [2-(alkyloxy)phenyl]-2-(1-piperidinyl)ethylesters of carbamic acid (CnA) were obtained by X-ray diffraction, and the bilayer thickness in extruded unilamellar dioleoylphosphatidylcholine vesicles containing C12NO was obtained by the neutron scattering. The values of d(L), d(pp/inf> and A(L) change linearly up to the 1:1 amphiphile:lipid molar ratio. The slopes of these dependencies increase for d(L) and d(pp/inf> and decrease for AL) with an increasing number of carbons n in the amphiphile long hydrocarbon substituent (18> or =n> or =8 for CnNO, 16> or =n> or =9 for GSn, 12> or =n> or =5 for CnA), while the opposite trends are observed for the short substituent (8> or =n>/=6 for CnNO, 9> or =n> or =7 for GSn, 5> or =n> or =3 for CnA).

Packing characteristics of a model system mimicking cytoplasmic bacterial membranes.

The phase diagram of fully hydrated mixtures of dipalmitoylphosphatidylethanolamine and -phosphatidylglycerol was constructed and the coexistence lines of the solidus and liquidus curve calculated based on regular solution theory using two nonideality parameters for each of the phase to account for nonideal and nonsymmetric mixing. Both lipids show nonideal miscibility in the liquid-crystalline phase, while a region of immiscibility exists in the lamellar-gel phase between the mole fraction x(DPPE)=0.05-0.

X-ray studies on the interaction of the antimicrobial peptide gramicidin S with microbial lipid extracts: evidence for cubic phase formation.

We have investigated the effect of the interaction of the antimicrobial peptide gramicidin S (GS) on the thermotropic phase behavior of model lipid bilayer membranes generated from the total membrane lipids of Acholeplasma laidlawii B and Escherichia coli. The A. laidlawii B membrane lipids consist primarily of neutral glycolipids and anionic phospholipids, while the E.