1,721,038 research outputs found
Probing the interplay between amyloidogenic proteins and membranes using lipid monolayers and bilayers
No full textMany degenerative diseases such as Alzheimer's and Parkinson's involve proteins that have a tendency to misfold
and aggregate eventually forming amyloid fibers. This review describes the use of monolayers, bilayers, supported
membranes, and vesicles as model systems that have helped elucidate the mechanisms and consequences of the
interactions between amyloidogenic proteins and membranes. These are twofold: membranes favor the formation of amyloid structures and these induce damage in those membranes.We describe studies that showhow interfaces, especially charged ones, favor amyloidogenic protein aggregation by several means. First, surfaces increase the effective protein concentration reducing a three-dimensional system to a two-dimensional one. Second, charged surfaces allow electrostatic interactions with the protein. Anionic lipids as well as rafts, rich in cholesterol and gangliosides, prove to play an especially important role. Finally, these amphipathic systems also offer a hydrophobic environment favoring conformational changes, oligomerization, and eventual formation of mature fibers. In addition,we examine severalmodels for membrane permeabilization: protein pores, leakage induced by extraction of lipids, chaotic pores, and membrane tension, presenting illustrative examples of experimental evidence in support of these models. The picture that emerges from recent work is one where more than one mechanism is in play. Which mechanism prevails depends on the protein, its aggregation state, and the lipid environment in which the interactions occur
Structure and permeability properties of biomimetic membranes of bolaform archaeal tetraether lipids.
No full textThis review is a general survey of the properties of membranes formed by tetraether lipids extracted from microorganisms living in extreme conditions, named Archaea. After describing the unusual structure and physico-chemical properties of the membrane-spanning lipids, which allow Archaea to maintain membrane integrity in harsh environments, we consider their molecular organization in model systems such as monolayers, artificial black membranes and liposomes. The latter, due to their remarkable thermal stability, can lead to attractive biotechnological applications.
Membrane permeability, local membrane fluidity and packing characteristics are reviewed with the aim of correlating structural features to permeability properties. In particular, studies on the very low passive proton permeation and leakage of entrapped molecules are reported and discussed in terms of membrane structure. Work on synthetic tetraether compounds is also reported
Effects of unstirred layers on the steady-state zero-current conductance of bilayer membranes mediated by neutral carriers of ions.
No full textSome effects of diffusion polarization and chemical reactions on the steady-state zero-current conductance of lipid bilayers mediated by neutral carriers of ions have been studied theoretically and experimentally. Assuming that ion permeation across the interfaces occurs via a heterogeneous reaction between ions in the solution and carriers in the membrane, the relationship between the conductance and the aqueous concentration of carriers is shown to be linear only in a limited range of sufficiently low concentrations. At higher carrier concentrations, which for the most strongly bound cations are within the range of the experimentally accessible values, the conductance is expected to become limited by diffusion of the carried ion in the unstirred layers and therefore reach an upper limiting value independent of the membrane properties. This expectation has been successfully verified for glyceryl-monooleate membranes in the presence of the ions K+, Rb+ and NH+4 and carriers such as valinomycin and trinactin. The experimental results support, at least for the present system, the generally accepted view that complexation between ions and the macrocyclic antibiotics occurs at the membrane surface; it is shown, in fact, that for a different mechanism, such as that by which the complexes would form in the aqueous solutions and cross the interfaces as lipid-soluble ions, the same type of saturation would be expected to be observable only for unrealistically high values of the rate constants of the ion-carrier association. A previously proposed criterion to distinguish between these two mechanisms, based on the dependence of the conductance on the ion concentration, is discussed from the viewpoint of this more comprehensive model
Asymmetric black membranes formed by one monolayer of bipolar lipids at the air-water interface
No full textIn this work a new technique is presented for the formation of black lipid membranes from a single monolayer of bipolar lipids at the air/water interface. The lipid, extracted from the thermophilic archaeobacterium Sulfolobus solfataricus, is characterized by two different polar heads. The membrane is formed with a technique similar to that introduced by Mental and Mueller; however, the lipid is spread only on one side of the teflon partition. Conductance in the presence of valinomycin, voltage-dependent capacitance, current-voltage measurements and electroporation indicate that, as expected, the membrane is asymmetric
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