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Tobias Weidner - One of the best experts on this subject based on the ideXlab platform.

  • a trough for improved sfg spectroscopy of Lipid Monolayers
    Review of Scientific Instruments, 2017
    Co-Authors: Johannes Franz, Marcjan Van Zadel, Tobias Weidner
    Abstract:

    Lipid Monolayers are indispensable model systems for biological membranes. The main advantage over bilayer model systems is that the surface pressure within the layer can be directly and reliably controlled. The sensitive interplay between surface pressure and temperature determines the molecular order within a model membrane and consequently determines the membrane phase behavior. The Lipid phase is of crucial importance for a range of membrane functions such as protein interactions and membrane permeability. A very reliable method to probe the structure of Lipid Monolayers is sum frequency generation (SFG) vibrational spectroscopy. Not only is SFG extremely surface sensitive but it can also directly access critical parameters such as Lipid order and orientation, and it can provide valuable information about protein interactions along with interfacial hydration. However, recent studies have shown that temperature gradients caused by high power laser beams perturb the Lipid layers and potentially obscure ...

  • A trough for improved SFG spectroscopy of Lipid Monolayers.
    The Review of scientific instruments, 2017
    Co-Authors: Johannes Franz, Marc-jan Van Zadel, Tobias Weidner
    Abstract:

    Lipid Monolayers are indispensable model systems for biological membranes. The main advantage over bilayer model systems is that the surface pressure within the layer can be directly and reliably controlled. The sensitive interplay between surface pressure and temperature determines the molecular order within a model membrane and consequently determines the membrane phase behavior. The Lipid phase is of crucial importance for a range of membrane functions such as protein interactions and membrane permeability. A very reliable method to probe the structure of Lipid Monolayers is sum frequency generation (SFG) vibrational spectroscopy. Not only is SFG extremely surface sensitive but it can also directly access critical parameters such as Lipid order and orientation, and it can provide valuable information about protein interactions along with interfacial hydration. However, recent studies have shown that temperature gradients caused by high power laser beams perturb the Lipid layers and potentially obscure the spectroscopic results. Here we demonstrate how the local heating problem can be effectively reduced by spatially distributing the laser pulses on the sample surface using a translating Langmuir trough for SFG experiments at Lipid Monolayers. The efficiency of the trough is illustrated by the detection of enhanced molecular order due to reduced heat load.

  • bovine and human insulin adsorption at Lipid Monolayers a comparison
    Frontiers in Physics, 2015
    Co-Authors: Sergio Mauri, Izabela Irena Rzeznicka, Tobias Weidner, Ravindra Pandey, Mischa Bonn, Hao Lu
    Abstract:

    Insulin is a widely used peptide in protein research and it is utilised as a model peptide to understand the mechanics of fibril formation, which is believed to be the cause of diseases such as Alzheimer and Creutzfeld-Jakob syndrome. Insulin has been used as a model system due to its biomedical relevance, small size and relatively simple tertiary structure. The adsorption of insu lin on a variety of surfaces has become the focus of numerous studies lately. These works have helped in elucidating the consequence of surface/protein hydrophilic/hydrophobic interaction in terms of protein refolding and aggregation. Unfortunately, such model surfaces differ significantly from physiological surfaces. Here we spectroscopically investigate the adsorption of insulin at Lipid Monolayers, to further our understanding of the interaction of insulin with biological surfaces. In particular we study the effect of minor mutations of insulin’s primary amino acid sequence on its interaction with 1,2-Dipalmitoyl-sn-glycero-3-phosphoglycerol (DPPG) model Lipid layers. We probe the structure of bovine and human insulin at the Lipid/water interface using sum frequency generation spectroscopy (SFG). The SFG experiments are complemented with XPS analysis of Langmuir-Schaefer deposited Lipid/insulin films. We find that bovine and human insulin, even though very similar in sequence, show a substantially different behavior when interacting with Lipid films.

  • formation of lysozyme oligomers at model cell membranes monitored with sum frequency generation spectroscopy
    Langmuir, 2014
    Co-Authors: I I Rzeźnicka, Michael Schleeger, Ravindra Pandey, Mischa Bonn, Tobias Weidner
    Abstract:

    A growing number of studies suggest that the formation of toxic oligomers, precursors of amyloid fibrils, is initiated at the cell membrane and not in the cytosolic compartments of the cell. Studies of membrane-induced protein oligomerization are challenging due to the difficulties of probing small numbers of proteins present at membrane surfaces. Here, we employ surface-sensitive vibrational sum frequency generation (VSFG) to investigate the secondary structure of lysozyme at the surface of Lipid Monolayers. We investigate lysozyme aggregation at negatively charged 1,2-dipalmitoyl-sn-glycero-3-(phospho-rac-1-glycerol) (DPPG) Lipid Monolayers under different pH conditions. The changes in the molecular vibrations of Lipids, proteins, and water as a function of pH and surface pressure allow us to simultaneously monitor details of the conformation state of lysozyme, the organization of Lipids, and the state of Lipid-bound water. At pH = 6 lysozyme induces significant disordering of the Lipid layer, and it ex...

Marjorie L Longo - One of the best experts on this subject based on the ideXlab platform.

  • collapse and shedding transitions in binary Lipid Monolayers coating microbubbles
    Langmuir, 2006
    Co-Authors: Mark A Borden, Marjorie L Longo
    Abstract:

    We report on a fluorescence microscopy study of the monolayer collapse and shedding behavior due to shell compression during the dissolution of air-filled, Lipid-coated microbubbles in degassed media. The monolayer shell was comprised of saturated diacyl phosphatidylcholine (C12:0 to C22:0) and an emulsifier, poly(ethylene glycol)-40 stearate. The morphologies of monolayer collapse structures and shed particles were monitored as a function of phosphoLipid acyl chain length (n) and temperature. The two components formed a single miscible phase when the phosphoLipid was near or above its main phase transition temperature, and collapse occurred via suboptical particles to vesicles (both were shed) and tubes as chain length increased. Conversely, two-phase coexistence was observed when the Lipid was below its main phase transition temperature. For these bubbles, a transition from primary collapse to secondary collapse was observed. Primary collapse was observed as a loss of expanded phase due to vesiculation. Secondary collapse involved the rapid propagation of monolayer folds and simultaneous deformation. For very rigid Monolayers, we observed substantial surface buckling with simultaneous nucleation and growth of folds. The folds merged at a single point or region, providing a conduit for the entire excess Lipid to shed in a single event, and the bubble smoothed and became more spherical. These results are discussed in the context of general binary phosphoLipid collapse behavior, microbubble dissolution behavior, medical applications, and the dissolution behavior of natural microbubbles.

  • oxygen permeability of fully condensed Lipid Monolayers
    Journal of Physical Chemistry B, 2004
    Co-Authors: Mark A Borden, Marjorie L Longo
    Abstract:

    The oxygen permeation resistance of highly condensed Monolayers composed of a homologous series of saturated diacyl phosphatidylcholine Lipids was measured using a novel technique that combined micromanipulation and electrochemical techniques. The use of Lipid monolayer-coated air microbubbles allowed measurement of the oxygen permeation resistance of fully condensed Lipid Monolayers that were previously unavailable using classical film balance techniques. Fully condensed Lipid Monolayers were found to significantly impede oxygen transport from the gas core, an effect that increased with Lipid acyl chain length. The magnitudes of the measured oxygen permeation resistances, 102 to 103 s/cm, agree with literature values for various gases permeating through highly condensed fatty acid and alcohol Monolayers. Such high resistances can account for the previously observed hindered dissolution of Lipid-stabilized microbubbles in degassed media. Additionally, the ability to probe a Lipid monolayer in its fully co...

  • Oxygen Permeability of Fully Condensed Lipid Monolayers
    The Journal of Physical Chemistry B, 2004
    Co-Authors: Mark A Borden, Marjorie L Longo
    Abstract:

    The oxygen permeation resistance of highly condensed Monolayers composed of a homologous series of saturated diacyl phosphatidylcholine Lipids was measured using a novel technique that combined micromanipulation and electrochemical techniques. The use of Lipid monolayer-coated air microbubbles allowed measurement of the oxygen permeation resistance of fully condensed Lipid Monolayers that were previously unavailable using classical film balance techniques. Fully condensed Lipid Monolayers were found to significantly impede oxygen transport from the gas core, an effect that increased with Lipid acyl chain length. The magnitudes of the measured oxygen permeation resistances, 10 2 to 10 3 s/cm, agree with literature values for various gases permeating through highly condensed fatty acid and alcohol Monolayers. Such high resistances can account for the previously observed hindered dissolution of Lipid-stabilized microbubbles in degassed media. Additionally, the ability to probe a Lipid monolayer in its fully condensed state leads to new physical insights into monolayer permeation.

Mark A Borden - One of the best experts on this subject based on the ideXlab platform.

  • collapse and shedding transitions in binary Lipid Monolayers coating microbubbles
    Langmuir, 2006
    Co-Authors: Mark A Borden, Marjorie L Longo
    Abstract:

    We report on a fluorescence microscopy study of the monolayer collapse and shedding behavior due to shell compression during the dissolution of air-filled, Lipid-coated microbubbles in degassed media. The monolayer shell was comprised of saturated diacyl phosphatidylcholine (C12:0 to C22:0) and an emulsifier, poly(ethylene glycol)-40 stearate. The morphologies of monolayer collapse structures and shed particles were monitored as a function of phosphoLipid acyl chain length (n) and temperature. The two components formed a single miscible phase when the phosphoLipid was near or above its main phase transition temperature, and collapse occurred via suboptical particles to vesicles (both were shed) and tubes as chain length increased. Conversely, two-phase coexistence was observed when the Lipid was below its main phase transition temperature. For these bubbles, a transition from primary collapse to secondary collapse was observed. Primary collapse was observed as a loss of expanded phase due to vesiculation. Secondary collapse involved the rapid propagation of monolayer folds and simultaneous deformation. For very rigid Monolayers, we observed substantial surface buckling with simultaneous nucleation and growth of folds. The folds merged at a single point or region, providing a conduit for the entire excess Lipid to shed in a single event, and the bubble smoothed and became more spherical. These results are discussed in the context of general binary phosphoLipid collapse behavior, microbubble dissolution behavior, medical applications, and the dissolution behavior of natural microbubbles.

  • oxygen permeability of fully condensed Lipid Monolayers
    Journal of Physical Chemistry B, 2004
    Co-Authors: Mark A Borden, Marjorie L Longo
    Abstract:

    The oxygen permeation resistance of highly condensed Monolayers composed of a homologous series of saturated diacyl phosphatidylcholine Lipids was measured using a novel technique that combined micromanipulation and electrochemical techniques. The use of Lipid monolayer-coated air microbubbles allowed measurement of the oxygen permeation resistance of fully condensed Lipid Monolayers that were previously unavailable using classical film balance techniques. Fully condensed Lipid Monolayers were found to significantly impede oxygen transport from the gas core, an effect that increased with Lipid acyl chain length. The magnitudes of the measured oxygen permeation resistances, 102 to 103 s/cm, agree with literature values for various gases permeating through highly condensed fatty acid and alcohol Monolayers. Such high resistances can account for the previously observed hindered dissolution of Lipid-stabilized microbubbles in degassed media. Additionally, the ability to probe a Lipid monolayer in its fully co...

  • Oxygen Permeability of Fully Condensed Lipid Monolayers
    The Journal of Physical Chemistry B, 2004
    Co-Authors: Mark A Borden, Marjorie L Longo
    Abstract:

    The oxygen permeation resistance of highly condensed Monolayers composed of a homologous series of saturated diacyl phosphatidylcholine Lipids was measured using a novel technique that combined micromanipulation and electrochemical techniques. The use of Lipid monolayer-coated air microbubbles allowed measurement of the oxygen permeation resistance of fully condensed Lipid Monolayers that were previously unavailable using classical film balance techniques. Fully condensed Lipid Monolayers were found to significantly impede oxygen transport from the gas core, an effect that increased with Lipid acyl chain length. The magnitudes of the measured oxygen permeation resistances, 10 2 to 10 3 s/cm, agree with literature values for various gases permeating through highly condensed fatty acid and alcohol Monolayers. Such high resistances can account for the previously observed hindered dissolution of Lipid-stabilized microbubbles in degassed media. Additionally, the ability to probe a Lipid monolayer in its fully condensed state leads to new physical insights into monolayer permeation.

Zhan Chen - One of the best experts on this subject based on the ideXlab platform.

  • Sum Frequency Generation of Interfacial Lipid Monolayers Shows Polarization Dependence on Experimental Geometries
    Langmuir : the ACS journal of surfaces and colloids, 2016
    Co-Authors: Yong Hao, Xiaofeng Han, Zhirui Guo, Zhan Chen
    Abstract:

    Sum frequency generation (SFG) vibrational spectroscopy has been widely employed to investigate molecular structures of biological surfaces and interfaces including model cell membranes. A variety of Lipid Monolayers or bilayers serving as model cell membranes and their interactions with many different molecules have been extensively studied using SFG. Here, we conducted an in-depth investigation on polarization-dependent SFG signals collected from interfacial Lipid Monolayers using different experimental geometries, i.e., the prism geometry (total internal reflection) and the window geometry (external reflection). The different SFG spectral features of interfacial Lipid Monolayers detected using different experimental geometries are due to the interplay between the varied Fresnel coefficients and second-order nonlinear susceptibility tensor terms of different vibrational modes (i.e., ss and as modes of methyl groups), which were analyzed in detail in this study. Therefore, understanding the interplay bet...

  • in situ molecular level studies on membrane related peptides and proteins in real time using sum frequency generation vibrational spectroscopy
    Journal of Structural Biology, 2009
    Co-Authors: Khoi Nguyen, Stephanie Le V Clair, Zhan Chen
    Abstract:

    Sum frequency generation (SFG) vibrational spectroscopy has been demonstrated to be a powerful technique to study the molecular structures of surfaces and interfaces in different chemical environments. This review summarizes recent SFG studies on hybrid bilayer membranes and substrate-supported Lipid Monolayers and bilayers, the interaction between peptides/proteins and Lipid Monolayers/bilayers, and bilayer perturbation induced by peptides/proteins. To demonstrate the ability of SFG to determine the orientations of various secondary structures, studies on the interactions between different peptides/proteins (melittin, G proteins, alamethicin, and tachyplesin I) and Lipid bilayers are discussed. Molecular level details revealed by SFG in these studies show that SFG can provide a unique understanding on the interactions between a Lipid monolayer/bilayer and peptides/proteins in real time, in situ and without any exogenous labeling.

  • sum frequency generation vibrational spectroscopy studies on molecular conformation and orientation of biological molecules at interfaces
    International Journal of Modern Physics B, 2005
    Co-Authors: Xiaoyun Chen, Matthew L Clarke, Jie Wang, Zhan Chen
    Abstract:

    Sum frequency generation (SFG) vibrational spectroscopy has been employed to study a variety of interesting biological phenomena occurring at interfaces. This review summarizes recent SFG studies on proteins, Lipid Monolayers and bilayers, and other biological molecules. Molecular level details revealed by SFG in these studies show that SFG is a powerful technique for characterizing conformation, orientation and ordering of biological molecules at interfaces.

William Margolin - One of the best experts on this subject based on the ideXlab platform.

  • gain of function variants of ftsa form diverse oligomeric structures on Lipids and enhance ftsz protofilament bundling
    Molecular Microbiology, 2018
    Co-Authors: Kara M Schoenemann, Marcin Krupka, Veronica W Rowlett, Steven L Distelhorst, William Margolin
    Abstract:

    Escherichia coli requires FtsZ, FtsA and ZipA proteins for early stages of cell division, the latter two tethering FtsZ polymers to the cytoplasmic membrane. Hypermorphic mutants of FtsA such as FtsA* (R286W) map to the FtsA self-interaction interface and can bypass the need for ZipA. Purified FtsA forms closed minirings on Lipid Monolayers that antagonize bundling of FtsZ protofilaments, whereas FtsA* forms smaller oligomeric arcs that enable bundling. Here, we examined three additional FtsA*-like mutant proteins for their ability to form oligomers on Lipid Monolayers and bundle FtsZ. Surprisingly, all three formed distinct structures ranging from mostly arcs (T249M), a mixture of minirings, arcs and straight filaments (Y139D) or short straight double filaments (G50E). All three could form filament sheets at higher concentrations with added ATP. Despite forming these diverse structures, all three mutant proteins acted like FtsA* to enable FtsZ protofilament bundling on Lipid Monolayers. Synthesis of the FtsA*-like proteins in vivo suppressed the toxic effects of a bundling-defective FtsZ, exacerbated effects of a hyper-bundled FtsZ, and rescued some thermosensitive cell division alleles. Together, the data suggest that conversion of FtsA minirings into any type of non-miniring oligomer can promote progression of cytokinesis through FtsZ bundling and other mechanisms.

  • escherichia coli ftsa forms Lipid bound minirings that antagonize lateral interactions between ftsz protofilaments
    Nature Communications, 2017
    Co-Authors: Marcin Krupka, Kara M Schoenemann, Veronica W Rowlett, Dustin R Morado, Heidi Vitrac, Jun Liu, William Margolin
    Abstract:

    The actin-like protein FtsA and the tubulin-like protein FtsZ play crucial roles during cell division in most bacteria. Here, the authors show that FtsA forms minirings on Lipid Monolayers, and present evidence supporting that its oligomeric state modulates the bundling o…