Incorporation of synthetic peptide helices in membranes of tetraether lipids from Thermoplasma acidophilum. A calorimetric study

The Main (Glyco) Phospholipid (MPL) of Thermoplasma acidophilum

The main phospholipid (MPL) of Thermoplasma acidophilum DSM 1728 was isolated, purified and physico-chemically characterized by differential scanning calorimetry (DSC)/differential thermal analysis (DTA) for its thermotropic behavior, alone and in mixtures with other lipids, cholesterol, hydrophobic peptides and pore-forming ionophores. Model membranes from MPL were investigated; black lipid membrane, Langmuir-Blodgett monolayer, and liposomes. Laboratory results were compared to computer simulation. MPL forms stable and resistant liposomes with highly proton-impermeable membrane and mixes at certain degree with common bilayer-forming lipids. Monomeric bacteriorhodopsin and ATP synthase from Micrococcus luteus were co-reconstituted and light-driven ATP synthesis measured. This review reports about almost four decades of research on Thermoplasma membrane and its MPL as well as transfer of this research to Thermoplasma species recently isolated from Indonesian volcanoes.

An index of lipid phase diagrams

There is a growing awareness of the utility of lipid phase behavior data in studies of membrane-related phenomena. Such miscibility information is commonly reported in the form of temperature-composition (T-C) phase diagrams. The current index is a conduit to the relevant literature. It lists lipid phase diagrams, their components and conditions of measurement, and complete bibliographic information. The main focus of the index is on lipids of membrane origin where water is the dispersing medium. However, it also includes records on acylglycerols, fatty acids, cationic lipids, and detergent-containing systems. The miscibility of synthetic and natural lipids with other lipids, with water, and with biomolecules (proteins, nucleic acids, carbohydrates, etc.) and non-biological materials (drugs, anesthetics, organic solvents, etc.) is within the purview of the index. There are 2188 phase diagram records in the index, the bulk (81%) of which refers to binary (two-component) T-C phase diagrams. The remainder is made up of more complex (ternary, quaternary) systems, pressure-T phase diagrams, and other more exotic miscibility studies. The index covers the period from 1965 through to July, 2001.

Reconstitution of bacteriorhodopsin and ATP synthase from Micrococcus luteus into liposomes of the purified main tetraether lipid from Thermoplasma acidophilum: proton conductance and light-driven ATP synthesis

The archaebacterium Thermoplasma acidophilum is cultivated at 59 degrees C in a medium containing sulfuric acid of pH 2. The purified bipolar membrane spanning main phospholipid (MPL) of this organism can be used to produce stable liposomes of 100-500 nm in diameter either using a French pressure cell detergent dialysis or sonication. Despite a potassium diffusion potential of 186 mV very low ionic permeability of sonicated MPL liposomes was measured using the potassium binding fluorescent indicator benzofuran isophthalate PBF1, which measures net K+ uptake. The latter also remained very low, in the presence of the K(+) ionophore valinomycin and palmitic acid. Addition of valinomycin and the potent uncoupler carbonylcyanid-p-trifluormehoxyphenyl-hydrazone (FCCP), led to a stimulation in potassium uptake. The rate of proton flux can be calculated from the net K(+) uptake. Under these conditions MPL liposomes are 1-2 orders of magnitude less permeable than egg yolk lecithin vesicles. The difference in proton permeability becomes even more pronounced with increasing temperature, examined using the fluorescent pH indicator pyranine. Purified bacteriorhodopsin from Halobacterium halobium was reconstituted into MPL liposomes in order to study the light-driven proton uptake in 150 mM KCl following addition of valinomycin, gramicidin, FCCP and Triton X-100. The light-driven proton transport into the liposomes was increased 30-fold by addition of valinomycin decreased by gramicidin and FCCP, and abolished by Triton X-100. Co-reconstituted MPL proteoliposomes containing bacteriorhodopsin and ATP synthase from Micrococcus luteus were capable of light-driven ATP synthesis demonstrating the functional coupling of proton transport and nucleotide generation in liposomal MPL membranes.

Interaction of phospholipids with proteins and peptides. New advances III

1. The review deals with the recent achievements in the study of the various interactions of phospholipids with proteins and peptides. 2. The interactions are classified according to the hydrophobic, hydrophilic or mixed character of the interactive forces. 3. The effect of the interaction on the structure and biological activity of the interacting molecules is also discussed.

Calorimetry of tetraether lipids from Thermoplasma acidophilum: incorporation of alamethicin, melittin, valinomycin, and nonactin

The development and application of model membrane systems on the basis of tetraether lipids from Thermoplasma acidophilum has been proposed. In this respect incorporation of membrane proteins and ionophores is indispensable and is demonstrated in the case of alamethicin, melittin, nonactin, and valinomycin by calorimetry. Dipalmitoylphosphatidylcholine (DPPC) and dihexadecylmaltosylglycerol (DHMG) were chosen for comparison. Melittin and alamethicin prove to broaden the lipid phase transition and to reduce the melting temperature Tm and enthalpy change (delta H) of the main phospholipid from T. acidophilum (MPL) and DPPC. The decrease in Tm, however, is more pronounced in DPPC than in MPL. Valinomycin shows only a marginal effect on the temperature and width of the transition; delta H is reduced in MPL and remains constant in DPPC and DHMG. With nonactin the phase transition of DPPC is quenched, and delta H and the half-height width are increased. DHMG is affected to a lesser extent and MPL only marginally. The four ionophores exhibit different modulation of the phase transition behavior of the various lipids as expected from their varying molecular structures. Thus, the integral membrane protein alamethicin, the peripheral protein melittin, valinomycin, and nonactin interact primarily with lipid head groups and are readily incorporated into the tetraether lipid structures.