RESUMO
This report presents evidence that the following Solanum steroids: solasodine, diosgenin and solanine interact with human erythrocytes and molecular models of their membranes as follows: a) X-ray diffraction studies showed that the compounds at low molar ratios (0.1-10.0mol%) induced increasing structural perturbation to dimyristoylphosphatidylcholine bilayers and to a considerable lower extent to those of dimyristoylphosphatidylethanolamine; b) differential scanning calorimetry data showed that the compounds were able to alter the cooperativity of dimyristoylphosphatidylcholine, dimyristoylphosphatidylethanolamine and dimyristoylphosphatidylserine phase transitions in a concentration-dependent manner; c) in the presence of steroids, the fluorescence of Merocyanine 540 incorporated to the membranes decreased suggesting a fluidization of the lipid system; d) scanning electron microscopy observations showed that all steroids altered the normal shape of human erythrocytes inducing mainly echinocytosis, characterized by the formation of blebs in their surfaces, an indication that their molecules are located into the outer monolayer of the erythrocyte membrane.
Assuntos
Diosgenina/química , Membrana Eritrocítica/química , Bicamadas Lipídicas/química , Alcaloides de Solanáceas/química , Solanina/química , Varredura Diferencial de Calorimetria , Dimiristoilfosfatidilcolina/química , Diosgenina/farmacologia , Membrana Eritrocítica/efeitos dos fármacos , Corantes Fluorescentes/química , Humanos , Microscopia Eletrônica de Varredura , Transição de Fase/efeitos dos fármacos , Fosfatidiletanolaminas/química , Fosfatidilserinas/química , Pirimidinonas/química , Espalhamento a Baixo Ângulo , Alcaloides de Solanáceas/farmacologia , Solanina/farmacologia , Difração de Raios XRESUMO
In the present work we have analyzed the effect of StAsp-PSI (plant-specific insert of potato aspartic protease) on the structural and thermotropic properties of the major phospholipid types of bacterial and animal cells. Results obtained suggest that StAsp-PSI induces a destabilization of the membrane bilayers, depending on the time of interaction between the protein and the bilayers, rather than on its concentration. This temporal delay would be consistent with a lateral diffusion of StAsp-PSI monomers to assemble into aggregates to form pores. Like with the results previously reported for the StAsp-PSI circular dichroism, data obtained here from IR spectroscopy show that there are slight changes in the StAsp-PSI secondary structure in the presence of lipid membranes; suggesting that these changes could be related with the StAsp-PSI self-association. Results obtained from steady-state fluorescence anisotropy and differential scanning calorimetry assays suggest that StAsp-PSI interacts with both uncharged and negatively charged phospholipids, modulates the phase polymorphic behavior of model membranes and partitions and buries differentially in the membrane depending on the presence of negatively charged phospholipids.
Assuntos
Ácido Aspártico Proteases/química , Bicamadas Lipídicas/química , Proteínas de Plantas/química , Solanum tuberosum/química , Ácido Aspártico Proteases/genética , Ácido Aspártico Proteases/metabolismo , Varredura Diferencial de Calorimetria , Dimiristoilfosfatidilcolina/química , Escherichia coli/genética , Escherichia coli/metabolismo , Permeabilidade , Fosfatidilgliceróis/química , Fosfatidilserinas/química , Proteínas de Plantas/genética , Proteínas de Plantas/metabolismo , Estrutura Secundária de Proteína , Proteínas Recombinantes/química , Proteínas Recombinantes/genética , Proteínas Recombinantes/metabolismo , Espectrofotometria InfravermelhoRESUMO
This work analyzes the surface properties of PE-containing membranes modified at the head group region by the addition of methyl and ethyl residues at or near the amine group. These residues alter the lipid-lipid and lipid-water interactions by changes in the hydrogen bonding capability and the charge density of the amine group thus affecting the electrostatic interaction. The results obtained by measuring the dipole potential, the zeta potential, the area per lipid and the compressibility properties allow to conclude that the H-bonding capability prevails in the lipid-lipid interaction. The non polar groups attached to the C2-carbon of the ethanolamine chain introduces a steric hindrance against compression and increases the dipole potential. The analysis of areas suggests that lipids with methylated head groups have a much larger compressibility at expense of the elimination of hydration water, which is congruent with the broader extent of the hysteresis loop.
Assuntos
Fosfatidiletanolaminas/química , Dimiristoilfosfatidilcolina/química , Etanolamina/química , Ligação de Hidrogênio , Água/químicaRESUMO
Sticholysins (Sts) I and II (StI/II) are pore-forming toxins (PFTs) produced by the Caribbean Sea anemone Stichodactyla helianthus belonging to the actinoporin family, a unique class of eukaryotic PFTs exclusively found in sea anemones. The role of lipid phase co-existence in the mechanism of the action of membranolytic proteins and peptides is not clearly understood. As for actinoporins, it has been proposed that phase separation promotes pore forming activity. However little is known about the effect of sticholysins on the phase separation of lipids in membranes. To gain insight into the mechanism of action of sticholysins, we evaluated the effect of these proteins on lipid segregation using differential scanning calorimetry (DSC) and atomic force microscopy (AFM). New evidence was obtained reflecting that these proteins reduce line tension in the membrane by promoting lipid mixing. In terms of the relevance for the mechanism of action of actinoporins, we hypothesize that expanding lipid disordered phases into lipid ordered phases decreases the lipid packing at the borders of the lipid raft, turning it into a more suitable environment for N-terminal insertion and pore formation.