scholarly journals Thiazolidinedione insulin sensitizers alter lipid bilayer properties and voltage-dependent sodium channel function: implications for drug discovery

2011 ◽  
Vol 138 (2) ◽  
pp. 249-270 ◽  
Author(s):  
Radda Rusinova ◽  
Karl F. Herold ◽  
R. Lea Sanford ◽  
Denise V. Greathouse ◽  
Hugh C. Hemmings ◽  
...  
Keyword(s):  
Lipid Bilayer ◽  
Lipid Bilayers ◽  
Gene Activation ◽  
Transport Processes ◽  
Titration Calorimetry ◽  
Peroxisome Proliferator ◽  
Inactivation Curve ◽  
Channel Function ◽  
Voltage Dependent ◽  
Target Effects

The thiazolidinediones (TZDs) are used in the treatment of diabetes mellitus type 2. Their canonical effects are mediated by activation of the peroxisome proliferator–activated receptor γ (PPARγ) transcription factor. In addition to effects mediated by gene activation, the TZDs cause acute, transcription-independent changes in various membrane transport processes, including glucose transport, and they alter the function of a diverse group of membrane proteins, including ion channels. The basis for these off-target effects is unknown, but the TZDs are hydrophobic/amphiphilic and adsorb to the bilayer–water interface, which will alter bilayer properties, meaning that the TZDs may alter membrane protein function by bilayer-mediated mechanisms. We therefore explored whether the TZDs alter lipid bilayer properties sufficiently to be sensed by bilayer-spanning proteins, using gramicidin A (gA) channels as probes. The TZDs altered bilayer elastic properties with potencies that did not correlate with their affinity for PPARγ. At concentrations where they altered gA channel function, they also altered the function of voltage-dependent sodium channels, producing a prepulse-dependent current inhibition and hyperpolarizing shift in the steady-state inactivation curve. The shifts in the inactivation curve produced by the TZDs and other amphiphiles can be superimposed by plotting them as a function of the changes in gA channel lifetimes. The TZDs’ partition coefficients into lipid bilayers were measured using isothermal titration calorimetry. The most potent bilayer modifier, troglitazone, alters bilayer properties at clinically relevant free concentrations; the least potent bilayer modifiers, pioglitazone and rosiglitazone, do not. Unlike other TZDs tested, ciglitazone behaves like a hydrophobic anion and alters the gA monomer–dimer equilibrium by more than one mechanism. Our results provide a possible mechanism for some off-target effects of an important group of drugs, and underscore the importance of exploring bilayer effects of candidate drugs early in drug development.

Ion Channel Sensor on a Silicon Support

2004 ◽  
Vol 820 ◽  
Author(s):  
Michael Goryll ◽  
Seth Wilk ◽  
Gerard M. Laws ◽  
Stephen M. Goodnick ◽  
Trevor J. Thornton ◽  
...  
Keyword(s):  
Ion Channels ◽  
Ion Channel ◽  
Lipid Bilayer ◽  
Lipid Bilayers ◽  
Chemical Vapor ◽  
Fast Method ◽  
Fluorocarbon Films ◽  
Novel Approach ◽  
Voltage Dependent ◽  
Assembled Monolayers

AbstractWe are building a biosensor based on ion channels inserted into lipid bilayers that are suspended across an aperture in silicon. The process flow only involves conventional optical lithography and deep Si reactive ion etching to create micromachined apertures in a silicon wafer. In order to provide surface properties for lipid bilayer attachment that are similar to those of the fluorocarbon films that are currently used, we coated the silicon surface with a fluoropolymer using plasma-assisted chemical vapor deposition. When compared with the surface treatment methods using self-assembled monolayers of fluorocarbon chemicals, this novel approach towards modifying the wettability of a silicon dioxide surface provides an easy and fast method for subsequent lipid bilayer formation. Current-Voltage measurements on OmpF ion channels incorporated into these membranes show the voltage dependent gating action expected from a working porin ion channel.

scholarly journals Tentative Peptide‒Lipid Bilayer Models Elucidating Molecular Behaviors and Interactions Driving Passive Cellular Uptake of Collagen-Derived Small Peptides

Molecules ◽  
2021 ◽  
Vol 26 (3) ◽  
pp. 710
Author(s):  
Pathomwat Wongrattanakamon ◽  
Wipawadee Yooin ◽  
Busaban Sirithunyalug ◽  
Piyarat Nimmanpipug ◽  
Supat Jiranusornkul
Keyword(s):  
Lipid Bilayer ◽  
Lipid Bilayers ◽  
Mean Square Displacement ◽  
Dynamics Simulation ◽  
Coordinate Frame ◽  
Mean Square ◽  
Binding Modes ◽  
Small Peptides ◽  
Collagen Peptides ◽  
Electron Density Profiles

Collagen contains hydroxyproline (Hyp), which is a unique amino acid. Three collagen-derived small peptides (Gly-Pro-Hyp, Pro-Hyp, and Gly-Hyp) interacting across a lipid bilayer (POPC model membrane) for cellular uptakes of these collagen-derived small peptides were studied using accelerated molecular dynamics simulation. The ligands were investigated for their binding modes, hydrogen bonds in each coordinate frame, and mean square displacement (MSD) in the Z direction. The lipid bilayers were evaluated for mass and electron density profiles of the lipid molecules, surface area of the head groups, and root mean square deviation (RMSD). The simulation results show that hydrogen bonding between the small collagen peptides and plasma membrane plays a significant role in their internalization. The translocation of the small collagen peptides across the cell membranes was shown. Pro-Hyp laterally condensed the membrane, resulting in an increase in the bilayer thickness and rigidity. Perception regarding molecular behaviors of collagen-derived peptides within the cell membrane, including their interactions, provides the novel design of specific bioactive collagen peptides for their applications.

scholarly journals Lipid bilayer degradation induced by SARS-CoV-2 spike protein as revealed by neutron reflectometry

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Alessandra Luchini ◽  
Samantha Micciulla ◽  
Giacomo Corucci ◽  
Krishna Chaithanya Batchu ◽  
Andreas Santamaria ◽  
...  
Keyword(s):  
Lipid Bilayer ◽  
Lipid Bilayers ◽  
Membrane Lipids ◽  
Lipid Extraction ◽  
Specific Interaction ◽  
Structural Features ◽  
Supported Lipid Bilayers ◽  
Fusion Event ◽  
Angiotensin Converting Enzyme 2 ◽  
Neutron Reflection

AbstractSARS-CoV-2 spike proteins are responsible for the membrane fusion event, which allows the virus to enter the host cell and cause infection. This process starts with the binding of the spike extramembrane domain to the angiotensin-converting enzyme 2 (ACE2), a membrane receptor highly abundant in the lungs. In this study, the extramembrane domain of SARS-CoV-2 Spike (sSpike) was injected on model membranes formed by supported lipid bilayers in presence and absence of the soluble part of receptor ACE2 (sACE2), and the structural features were studied at sub-nanometer level by neutron reflection. In all cases the presence of the protein produced a remarkable degradation of the lipid bilayer. Indeed, both for membranes from synthetic and natural lipids, a significant reduction of the surface coverage was observed. Quartz crystal microbalance measurements showed that lipid extraction starts immediately after sSpike protein injection. All measurements indicate that the presence of proteins induces the removal of membrane lipids, both in the presence and in the absence of ACE2, suggesting that sSpike molecules strongly associate with lipids, and strip them away from the bilayer, via a non-specific interaction. A cooperative effect of sACE2 and sSpike on lipid extraction was also observed.

scholarly journals Surface roughness as rupture control factor of lipid vesicles

2013 ◽  
Vol 19 (S4) ◽  
pp. 107-108 ◽  
Author(s):  
A.A. Duarte ◽  
M. Raposo
Keyword(s):  
Lipid Bilayer ◽  
Lipid Bilayers ◽  
Biological Membrane ◽  
Substrate Surface ◽  
Lipid Vesicles ◽  
Planar Lipid Bilayer ◽  
Root Mean Square Roughness ◽  
Control Factor ◽  
Formation Mechanisms ◽  
Adsorbed Amount

Liposomes or lipid vesicles are self-closed structures formed by one or several concentric lipid bilayers with an aqueous phase inside, which may incorporate almost any molecule, namely proteins, hormones, enzymes, antibiotics, anticancer agents, antifungical agents, gene transfer agents, DNA, and whole viruses. Scientific evidences prove that unprotected liposomes containing drugs are easily released from the endoplasmic reticulum of the cell. To increase the vesicles lifetime and to activate a controlled drug release with an external stimulus, the vesicles immobilization on a surface and the factors which create conditions to the liposome rupture have to be analyzed. A number of studies have identified some of the critical stages of vesicle adsorption (adhesion), fusion, deformation, rupture, and spreading of the lipid bilayer. Nevertheless, the formation mechanisms of well-controlled continuous supported bilayers or adsorption of whole liposomes are still not fully understood. As yet it was demonstrated that a controlled adsorption of vesicles containing a small fraction of charged lipids occurs without rupture and their subsequent embedding in polyelectrolyte multilayer (PEM) films, meaning vesicles may be immobilized in an intact or slightly deformed state, which can act as drug reservoirs. Moreover, depending on the nature of the physicochemical conditions of the vesicle solution and the substrate surface, a flat lipid bilayer can be formed, known as supported lipid bilayers, which can incorporate membrane proteins and keep the native dynamics of the lipid bilayer mimicking a biological membrane. In this study, a layer of 1,2-dipalmitoyl-sn-glycero-3-[phospho-rac-(1-glycerol)] (sodium salt) (DPPG) liposomes adsorbed onto PEMs cushions based on poly(ethylenimine) (PEI), poly(sodium 4-styrenesulfonate) (PSS) and poly(allylamine hydrochloride) (PAH) polyelectrolytes was analyzed by atomic force microscopy (AFM) technique in non-contact mode and quartz crystal microbalance (QCM).Sequential heterostructures of Si/PEI(PSS/PAH)4 and Si/PAH, also designated cushions, were prepared onto silicon substrates using the layer-by-layer (LbL) technique with polyelectrolyte solutions of PEI, PSS and PAH of monomeric concentrations of 0.01M. Topographic images of 1×1μm2 area of Si/PAH/DPPG (Figure 1 a), and Si/PEI(PSS/PAH)4/DPPG (Figure 1 b) LbL films were acquired by AFM. The root mean square roughness (RMS) calculated from topographies data are listed in table I. As shown, when a DPPG layer is adsorbed onto Si/PAH the RMS keeps an approximately equal value meaning that the liposome disrupted and spread onto the surface forming a planar lipid bilayer. But when a DPPG layer is adsorbed onto Si/PEI(PSS/PAH)4 the RMS value doubled, indicating that the structural integrity of the liposomes is maintained, even though there has been any deformation during adsorption. The adsorbed amount of the two PEMs and DPPG-liposomes layers was measured using a QCM and is displayed in table I. The DPPG adsorbed amount obtained on the PAH cushion was approximately equal to a planar lipid bilayer, while the adsorption onto PEI(PSS/PAH)4 was higher than the predicted for a planar lipid bilayer. This behavior suggests that the DPPG liposomes on the second PEM remained intact during adsorption. Both confirm the AFM results. Therefore we conclude that the initial roughness of the surface is a primordial factor to determine the adsorption or not of intact vesicles.The authors acknowledge the “Fundação para a Ciência e Tecnologia” (FCT-MEC) by the post-graduate scholarship SFRH/BD/62229/2009 and the “Plurianual” funding.

Synaptic and Somatic Effects of Axotomy in the Intact, Innervated Rat Sympathetic Neuron

2006 ◽  
Vol 95 (5) ◽  
pp. 2832-2844 ◽  
Author(s):  
Oscar Sacchi ◽  
Maria Lisa Rossi ◽  
Rita Canella ◽  
Riccardo Fesce
Keyword(s):  
Sympathetic Neuron ◽  
Equilibrium Potential ◽  
Voltage Sensitivity ◽  
Inactivation Curve ◽  
Epsc Amplitude ◽  
Control Value ◽  
Voltage Dependent ◽  
Steady State Inactivation ◽  
Cervical Ganglia

A biophysical description of the axotomized rat sympathetic neuron is reported, obtained by the two-electrode voltage-clamp technique in mature, intact superior cervical ganglia in vitro. Multiple aspects of neuron functioning were tested. Synaptic conductance activated by the whole presynaptic input decreased to 29% of the control value (0.92 μS per neuron) 1 day after axotomy and to 18% after 3 days. Despite the decrease in amplitude of the macroscopic current, miniature excitatory postsynaptic current (mEPSC) mean conductance, acetylcholine (ACh) equilibrium potential, and EPSC decay time constant were unaffected. Synaptic efficacy was tested during paired-pulse or maintained stimulation (5, 10, and 15 Hz, 10-s duration). Quantal release in axotomized neurons was preserved during the tetanus despite the reduction of the initial EPSC amplitude, suggesting that ACh secretion depended on the number of surviving synapses; each of them exhibited dynamic behavior during trains similar to that of normal synapses. Facilitation of EPSC amplitude was noted in 2-day axotomized neurons during the first few impulses in the train. Voltage-dependent potassium currents (the delayed IKD and the transient IA) exhibited an early drastic decrease in peak amplitude; these effects persisted 7 days after axotomy. Marked changes in IA kinetics occurred after injury: the steady-state inactivation curve shifted by up to +17 mV toward positive potentials and the voltage sensitivity of inactivation removal became steeper. IA impairment was reflected in a reduced inward threshold charge for discharge and reduced spike repolarization rate. Synaptic and somatic data were applied in a mathematical model to describe the progressive decrease in the safety factor, and the eventual failure of ganglionic transmission after axotomy.

Vascular smooth muscle cell dysfunction in diabetes: nuclear receptors channel to relaxation

2016 ◽  
Vol 130 (20) ◽  
pp. 1837-1839 ◽  
Author(s):  
Geneviève Doyon ◽  
Dennis Bruemmer
Keyword(s):  
Cell Function ◽  
Vascular Dysfunction ◽  
Microvascular Disease ◽  
Peroxisome Proliferator ◽  
Peroxisome Proliferator Activated Receptor ◽  
Endothelial Cell Function ◽  
Cell Dysfunction ◽  
Kv Channels ◽  
Voltage Dependent ◽  
Patients With Diabetes

Endothelial dysfunction and impaired vascular relaxation represent a common cause of microvascular disease in patients with diabetes. Although multiple mechanisms underlying altered endothelial cell function in diabetes have been described, there is currently no specific and approved pharmacological treatment. In this edition of Clinical Science, Morales-Cano et al. characterize voltage-dependent K+ (Kv) channels as genes regulated by pharmacological activation of peroxisome proliferator-activated receptor-b/d (PPARb/d). Diabetes altered Kv channel function leading to impaired coronary artery relaxation, which was prevented by pharmacological activation of PPARb/d. These studies highlight an important mechanism of vascular dysfunction in diabetes and point to a potential approach for therapy, particularly considering that PPARb/d ligands have been developed and tested in small clinical trials.

scholarly journals Measuring anion binding at biomembrane interfaces

2021 ◽  
Author(s):  
Xin Wu ◽  
Patrick Wang ◽  
William Lewis ◽  
Yun-Bao Jiang ◽  
Philip Alan Gale
Keyword(s):  
Lipid Bilayers ◽  
Common Knowledge ◽  
Anion Recognition ◽  
Chloride Ions ◽  
Transport Processes ◽  
Anion Binding ◽  
Dihydrogen Phosphate ◽  
Materials Chemistry ◽  
Synthetic Receptor ◽  
Chemistry Research

Understanding non-covalent molecular recognition events at biomembrane interfaces is important in biological, medicinal, and materials chemistry research.1 Despite the crucial regulatory roles of anion binding/transport processes at biomembranes, no information is available regarding how strongly anions can bind to naturally occurring or synthetic receptors in lipid bilayer environments compared to their well-established behaviour in solutions.2 To bridge this knowledge gap, we synthesised a flat macrocycle that possesses a record aqueous SO42– affinity among neutral receptors and exploited its unique fluorescence response at interfaces. We show that the determinants of anion binding are extraordinarily different in organic solvents and in lipid bilayers. The high charge density of dihydrogen phosphate and chloride ions prevails in DMSO, however in lipids they fail to bind the macrocycle. Perchlorate and iodide hardly bind in DMSO but show significant affinities for the macrocycle in lipids. Our results demonstrate a surprisingly great advantage of large, charge-diffuse anions to bind to a lipid-embedded synthetic receptor mainly attributed to their higher polarisabilities and deeper penetration into the bilayer, beyond the common knowledge of dehydration energy-governed selectivity. The elucidation of these principles enhances our understanding of biological anion recognition functions in membranes and guides the design of ionophores and molecular machines operating at biomembrane interfaces.

scholarly journals Lipid bilayer induces contraction of the denatured state ensemble of a helical-bundle membrane protein

2021 ◽  
Vol 119 (1) ◽  
pp. e2109169119
Author(s):  
Kristen A. Gaffney ◽  
Ruiqiong Guo ◽  
Michael D. Bridges ◽  
Shaima Muhammednazaar ◽  
Daoyang Chen ◽  
...  
Keyword(s):  
Membrane Protein ◽  
Lipid Bilayer ◽  
Lipid Bilayers ◽  
Limited Proteolysis ◽  
Water Soluble ◽  
Disordered Proteins ◽  
Resonance Spectroscopy ◽  
Denatured State ◽  
E Coli ◽  
State Ensemble

Defining the denatured state ensemble (DSE) and disordered proteins is essential to understanding folding, chaperone action, degradation, and translocation. As compared with water-soluble proteins, the DSE of membrane proteins is much less characterized. Here, we measure the DSE of the helical membrane protein GlpG of Escherichia coli (E. coli) in native-like lipid bilayers. The DSE was obtained using our steric trapping method, which couples denaturation of doubly biotinylated GlpG to binding of two streptavidin molecules. The helices and loops are probed using limited proteolysis and mass spectrometry, while the dimensions are determined using our paramagnetic biotin derivative and double electron–electron resonance spectroscopy. These data, along with our Upside simulations, identify the DSE as being highly dynamic, involving the topology changes and unfolding of some of the transmembrane (TM) helices. The DSE is expanded relative to the native state but only to 15 to 75% of the fully expanded condition. The degree of expansion depends on the local protein packing and the lipid composition. E. coli’s lipid bilayer promotes the association of TM helices in the DSE and, probably in general, facilitates interhelical interactions. This tendency may be the outcome of a general lipophobic effect of proteins within the cell membranes.

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