Secondary structure and orientation of the pore-forming toxin lysenin in a sphingomyelin-containing membrane

AbstractLysenin is a sphingomyelin-recognizing toxin which forms stable oligomers upon membrane binding and causes cell lysis. To get insight into the mechanism of the transition of lysenin from a soluble to a membrane-bound form, surface activity of the protein and its binding to lipid membranes were studied using tensiometric measurements, Fourier-transform infrared spectroscopy (FTIR) and FTIR-linear dichroism. The results showed cooperative adsorption of recombinant lysenin-His at the argon–water interface from the water subphase which suggested self-association of lysenin-His in solution. An assembly of premature oligomers by lysenin-His in solution was confirmed by blue native gel electrophoresis. When a monolayer composed of sphingomyelin and cholesterol was present at the interface, the rate of insertion of lysenin-His into the monolayer was considerably enhanced. Analysis of FTIR spectra of soluble lysenin-His demonstrated that the protein contained 27% β-sheet, 28% aggregated β-strands, 10% α-helix, 23% turns and loops and 12% different kinds of aggregated forms. In membrane-bound lysenin-His the total content of α-helices, turns and loops, and β-structures did not change, however, the 1636cm−1 β-sheet band increased from 18% to 31% at the expense of the 1680cm−1 β-sheet structure. Spectral analysis of the amide I band showed that the α-helical component was oriented with at 41° to the normal to the membrane, indicating that this protein segment could be anchored in the hydrophobic core of the membrane

SOME OF TOPOLOGICAL AND METHODOLOGICAL ASPECTS OF QUANTUM COSMOLOGY MODELS

In this paper we address some critical remarks to two leading models quantum cosmology – Hawking-Hartle model and Vilenkin model. Both models appeal to different mathematical frame- works to reconstract of first moments of Universe ewolution. The first one presents wave function of the Universe using Feynman’s formalism of quantum mechanics — path integrals. The other one shows the beginnig of the Universe as quantum tunneling process. The authors of above mentioned approaches to quantum cosmology claims, that these mechanisms describe creation of the Universe ex nihilo. The main aim of tis paper is to show a weakness of such interpretations. Firstly, Gordon McCabe’s criticism is presented. His analyses are based on topological concept of cobordism. In the second step, we show that the concept of ex nihilo should be rather understood as “zero-point- geometry” with a material field.Artykuł prezentuje uwagi krytyczne pod adresem dwóch wiodących modeli kosmogenezy kwantowej – modelu Hawkinga – Hartle’a oraz modelu Vilenkina. Obydwa modele wykorzystują różne formalizmy w rekonstrukcji początkowych etapów ewolucji Wszechświata. Pierwszy konstruuje funkcję falową Wszechświata za pomocą feynmanowskiego całkowania po trajektoriach, natomiast drugi ukazuje pierwotną dynamikę Wszechświata jako efekt tunelowy. Twórcy obydwu koncepcji kosmologii kwantowej uważają, że prezentowane przez nich mechanizmy opisują kreację Wszechświata ex nihilo. Celem artykułu jest wskazanie na nieprawomocność takich wniosków. Najpierw zaprezentowana jest krytyka autorstwa Gordona McCabe’a, który swoje analizy opiera na topologicznym pojęciu kobordyzmu. Następnie wskazujemy na to, że stosowane w obu projektach pojęcie ex nihilo lepiej oddaje punkt geometryczny z zadanym polem materialnym

Gruszecki, Effect of antibiotic amphotericin B on structural and dynamic properties of lipid membranes formed with egg yolk phosphatidylcholine, Chem. Phys. Lipids 147

Abstract Amphotericin B (AmB) is a popular antibiotic applied in treatment of deep-seated mycotic infections. The mode of action of AmB is based upon interactions with biomembranes but exact binding properties of the antibiotic to the lipid membranes still remain obscure. Effect of incorporation of AmB into egg yolk phosphatidylcholine membranes in the concentration range from 0.01 to 5 mol% on structural and dynamic properties of lipid bilayers was studied with application of small-angle neutron scattering, X-ray diffractometry and Fourier-transform infrared spectroscopy (FTIR). The results of the experiments show that AmB is located predominantly in the headgroup region of the membranes at concentrations below 1 mol%. The process of AmB aggregation, at concentrations above 1 mol%, is associated with ordering effect within the acyl chain region and therefore indicates incorporation of AmB into the hydrophobic membrane core

Molecular organization of antifungal antibiotic amphotericin B in lipid monolayers studied by means of Fluorescence Lifetime Imaging Microscopy

International audienceAmphotericin B (AmB) is a life-saving polyene antibiotic used to treat deep-seated mycotic infections. Both the mode of therapeutic action as well as toxic side effects are directly dependent on molecular organization of the drug. Binding of AmB to lipid monolayers formed with dipalmitoylphosphatidylcholine, pure and containing 40 mol% cholesterol or ergosterol, the sterols of human and fungi respectively, has been examined by means of Fluorescence Lifetime Imaging Microscopy. AmB emits fluorescence with the characteristic lifetimes dependent on actual molecular organization: τ≤10 ps and τ=0.35 ns in the monomeric state, the emission from the S and the S states respectively and τ=14 ns and τ=3.5 ns in the form of a dimer and associated dimers respectively. Analysis of the Langmuir-Blodgett films reveals that AmB binds to the lipid membranes and to the cholesterol-containing lipid membranes preferentially in the form of associated dimers. The same form of AmB appears in the membranes containing ergosterol but additionally the monomers and dimers of the drug. can be observed, which can severely affect molecular organization of the lipid membrane. The results are discussed in terms of selectivity of AmB towards the ergosterol-containing biomembranes of fungi