1,721,092 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
Surface shear viscosity and phase transitions of monolayers at the air-water interface
No full textThe canal method has been employed to measure the in-plane steady shear viscosity of monolayers of bolaform lipids extracted from the membrane of the thermophilic microorganism Sulfolobus solfataricus. Monolayers were formed with the polar lipid extract (PLE), which is a mixture of several bolaform lipids, each one endowed with two nonequivalent polar headgroups. Viscosities were obtained from the measured flows by using the equation introduced by Joly; this equation contains a semiempirical parameter A, which takes into account the monolayer-subphase mechanical coupling. Measuring the flows for two different substances (PLE and oleic acid) and channel widths, the monolayer viscosities and the parameter A were determined at the same time. The analysis of the viscosity data according to the free area model shows evidences of the molecular conformational changes matching monolayer phase transitions
Organization of bipolar lipids at the air-water interface
No full textIn this paper we report the results of surface pressure-area measurements and fluorescence microscopy of Langmuir monolayers of bipolar lipids extracted from the thermophilic archaeobacterium Sulfolobus solfataricus. We have analysed the two-dimensional phase behaviour of the polar lipid extract, some of its subfractions and the hydrolytic fractions glycerol dialkyl glycerol tetraether (GDGT) and glycerol dialkyl nonitol tetraether (GDNT) in the temperature range 25-45-degrees-C. For comparison, films of diphytanoyl phosphatidylcholine were also studied. Only the isotherms of the polar lipid extract exhibit a plateau region. The molecular areas of GDGT and GDNT, even at the collapse pressure, are much larger than those of the other lipid fractions. For the former compounds a U-shaped hydrocarbon chain conformation mixed with an extended chain arrangement is suggested, while all the other fractions display always a vertical arrangement
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
Morphology changes of Si(001) surfaces during wet chemical halogenation
No full textThis paper reports an experimental study aimed to develop a suitable and reliable procedure to graft organic molecular fragments onto silicon surfaces, leading to a stable organic termination. Grafting of self-assembled organic films on the (0 0 1) surface of Si is performed by SC1/SC2 processing and by a bromination step preceding the nucleophilic reaction with the organic aromatic compound. After each wet processing step the Si(0 0 1) morphology is investigated using atomic force microscopy to correlate the etching chemistry and the substrate morphology. The bromination step is observed to cause a strong increase of surface roughness due to the formation of pyramid-shaped nanostructures. Controlling the surface roughness as induced by chemical processing is suggested as a fundamental goal towards an increase of the organic film coverage and stability. Correcting actions and enabling prevention of surface damage are proposed and discussed
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
Molecular dynamics simulation of the indentation of a crystalline surface by an atomic force microscope tip
No full textTrehalose interacts with phospholipid polar heads in Langmuir monolayers
No full textSurface pressure-area isotherms, surface potential-area isotherms and fluorescence microscopy were employed to study the behavior of phospholipid monolayers at the air/water interface when trehalose was added to the aqueous subphase. In the presence of this sugar, the critical area corresponding to the onset of surface potential increases, indicating that trehalose is participating in the network of hydrogen bonds between the phospholipid polar heads. In addition, it causes an expansion of the isotherm, hindering the formation of the liquid-condensed phase. The collapse area is significantly increased, indicating that trehalose takes part in the monolayer structure without being expelled even at high surface pressures. A quantitative comparison of the collapse areas and critical areas for surface potential in the presence and in the absence of the sugar shows that an almost fixed number of trehalose molecules interacts with the monolayer independently of the surface packing, thus indicating that the observed effects can be ascribed to a tight binding of trehalose to the polar heads in a defined ratio. No similar effects were observed in the presence of glucose. We rationalize the reported data in light of the water replacement hypothesis, developed to explain the preservation of biomembranes by trehalose; this hypothesis suggests that trehalose forms hydrogen bonds with the membrane polar headgroups, thus replacing the water of hydration at the membrane-fluid interface and maintaining the headgroups at their hydrated position
- …
