1,721,072 research outputs found
Unraveling lipid/protein interaction in model lipid bilayers by Atomic Force Microscopy
No full textThe current view of the biological membrane is that in which lipids and proteins mutually interact to accomplish membrane functions. The lateral heterogeneity of the lipid bilayer can induce partitioning of membrane-associated proteins, favoring protein-protein interaction and influence signaling and trafficking. The Atomic Force Microscope allows to study the localization of membrane-associated proteins with respect to the lipid organization at the single molecule level and without the need for fluorescence staining. These features make AFM a technique of choice to study lipid/protein interactions in model systems or native membranes. Here we will review the technical aspects inherent to and the main results obtained by AFM in the study of protein partitioning in lipid domains concentrating in particular on GPI-anchored proteins, lipidated proteins, and transmembrane proteins. Whenever possible, we will also discuss the functional consequences of what has been imaged by Atomic Force Microscopy
Phase transitions in supported lipid bilayers studied by AFM
No full textWe review the capabilities of Atomic Force Microscopy (AFM) in the study of phase transitions in Supported Lipid Bilayers (SLBs). AFM represents a powerful technique to cover the resolution range not available to fluorescence imaging techniques and where spectroscopic data suggest what the relevant lateral scale for domain formation might be. Phase transitions of lipid bilayers involve the formation of domains characterized by different heights with respect to the surrounding phase and are therefore easily identified by AFM in liquid solution once the bilayer is confined to a flat surface. Even if not endowed with high time resolution, AFM allows light to be shed on some aspects related to lipid phase transitions in the case of both a single lipid component and lipid mixtures containing sterols also. We discuss here the obtained results in light of the peculiarities of supported lipid bilayer model systems
Hydroquinone-Benzoquinone Redox Couple as a Versatile Element for Molecular Electronics
No full textThe possibility of controlling electron transport in a single molecule bridged between two metal electrodes represents the ultimate goal of molecular electronics. Molecular electronics aims also at introducing specific properties for the electron transport features both by controlling the structural details of the junction and by exploiting new chemical functionalities. Here we show that, in a molecular junction, where electrodes are represented by a gold substrate and the tip of a scanning tunneling microscope in electrochemical environment, the use of a single molecular species makes it possible to obtain different features for the tunneling current according to the structural details of the junction. In particular, molecules endowed with redox properties brought about by a hydroquinone/benzoquinone redox couple can show both transistor-like and negative differential resistance (NDR) effects. We discuss the mechanistic processes that might describe the different behavior in light of theories of electron transfer between metal electrodes and redox molecules. The results show, on the one hand, the great potential and flexibility that molecular electronics offer and, on the other hand, the need of controlling as much as possible the details of the tunneling junction in order to obtain reproducible results
AFM: a versatile tool in biophysics
No full textHere we review the applications of atomic force microscopy to the study of samples of biological origin. Emphasis is given to provide the reader with information on the broad range of different biophysical applications that, to date, such a technique can deal with. After recalling briefly the operating principles of an atomic force microscope, the broad field of bio-imaging applications is faced (DNA, DNA-protein interaction, proteins, lipid membranes, cells); thereafter, the use of the atomic force microscope to measure forces is introduced and force mapping on living cells is discussed. This section is followed by the description of the use of force curves in assessing single-molecule inter- and intramolecular interactions. A paragraph on the perspectives of the technique in biophysical applications concludes the paper. We hope that this review can help the reader in appreciating how atomic force microscopy contributes to the current explosive growth of nanobiosciences, where biology, chemistry and physics merge
Electron transfer in nanobiodevices
Full text linkThe present tutorial is aimed at introducing the reader to the main aspects of electron transfer in nanobiodevices. Nanobiodevices are faced both from scientific and technological viewpoints and their particular implementation as electron transfer devices provides the opportunity of presenting fundamentals of electron transfer theory. Examples of implementations of stand alone devices, along with those involving reconfigurable set-ups based on an electrochemical scanning tunneling microscope, enable introducing heterogeneous electron transfer and electron transport theories in electrochemical environment. Specific cases of nanobiodevices involving redox metalloproteins are reported and experimental results are interpreted and discussed in view of the most recent theoretical advancements, in order to provide the reader with a comprehensive view of the results and promises in this exciting branch of nanotechnology
AFM and FTIR Spectroscopy Investigation of the Inverted Hexagonal Phase of Cardiolipin
No full textAtomic force microscopy (AFM) and FTIR spectroscopy techniques have been exploited to investigate the inverted hexagonal phase (HII) of cardiolipin obtained by dehydration of a phospholipid water dispersion on a solid support. The characteristic cylinders of the HII phase have been imaged by AFM and the effects of different preparation conditions (temperature and the presence of chemicals) on the structural parameters and on the presence of local nanoscale defects have been studied. It has been found that the measured repeat spacing of the HII cylinders decreases upon increase of temperature and addition of pentachlorophenol (PCP), a chemical which is known to affect the structure and function of lipid bilayers. It has been shown that AFM can help in revealing some features of the mechanism of the inverted hexagonal phase formation, corroborating the results of a recent molecular dynamics study on the HII phase formation from multilamellar phospholipid structures
Method for estimating the cooperativity length in polymers
No full textThe problem of estimating the size of the cooperatively rearranging regions (CRRs) in supercooled polymeric melts from an analysis of the α-process in ordinary relaxation experiments is addressed. The mechanism whereby a CRR changes its configuration is viewed as consisting of two distinct steps: a reduced number of monomers reaches initially an activated state, allowing for some local rearrangement; then, the subsequent regression of the energy fluctuation may take place through the configurational degrees of freedom, thus allowing for further rearrangements on larger length scales. The latter are indeed those to which the well-known Donth's scheme refers. Local readjustments are described in the framework of a canonical formalism on a stationary ensemble of small-scale regions, distributed over all possible energy thresholds for rearrangement. Large-scale configurational changes, instead, are described as spontaneous processes. Two main regimes are envisaged, depending on whether the role played by the configurational degrees of freedom in the regression of the energy fluctuation is significant or not. It is argued that the latter case is related to the occurrence of an Arrhenian dependence of the central relaxation rate. Consistency with Donth's scheme is demonstrated, and data from the literature confirm the agreement of the two methods of analysis when configurational degrees of freedom are relevant for the fluctuation regression. Poly(n-butyl methacrylate) is chosen in order to show how CRR size and temperature fluctuations at rearrangement can be estimated from stress relaxation experiments carried out by means of an atomic force microscopy setup. Cases in which the configurational pathway for regression is significantly hindered are considered. Relaxation in poly(dimethyl siloxane) confined in nanopores is taken as an example to suggest how a more complete view of the effects of configurational constraints would be possible if direct measurements of temperature fluctuations were combined with the proposed analysis
EC-STM/STS of Redox Metalloproteins and Co-factors
No full textThis chapter is intended to review some of the main experimental and theoretical results in the field of single molecule characterization of the electron transport through redox adsorbates. Both redox metalloproteins and co-factors have been object of intense investigation by EC-STM/STS techniques. Particularly, the paradigmatic case of the redox metalloprotein azurin and of derivatized quinone molecules adsorbed on atomically flat gold provide a valuable insight into the potential of the technique and into the attainable level of understanding of the electron transfer phenomenon. The results are discussed critically in view of their impact on the field of Molecular Electronics
Effects of the peptide Magainin H2 on Supported Lipid Bilayers studied by different biophysical techniques
No full textGiven the increasing trend in bacterial antibiotic resistance, research on antimicrobial peptides and their mechanisms of action has become of huge relevance in the last years. Several studies have investigated the effects of a large variety of antimicrobial peptides directly on bacteria or on model lipid bilayers. In the case of model lipid bilayers, different systems are typically exploited; however, different results could be obtained due to the specific properties of the used system. Supported Lipid Bilayers and Giant Unilamellar Vesicles are among the most popular model systems. Here we used Atomic Force Microscopy and fluorescence microscopy to study the interaction of the antimicrobial peptide Magainin H2, an analog of Magainin 2 with increased hydrophobicity, on Supported Lipid Bilayers. We found that, for this kind of model bilayer, due to its strong interaction with the support, the lateral expansion of the membrane induced by the interaction with the peptides is initially inhibited and subsequently proceeds creating new bilayer regions with many defects. This scenario gives rise in Supported Lipid Bilayers to effects like initial increase of lateral pressure, formation of lipid tubes to release this increase, or development of bilayer regions with lower lipid density. Our results highlight that care should be given to the selected model system when studying and comparing the interaction of peptides with other lipid bilayer model systems
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