scholarly journals Measurements of the effect of membrane asymmetry on the mechanical properties of lipid bilayers

2015 ◽  
Vol 51 (32) ◽  
pp. 6976-6979 ◽  
Author(s):  
Yuval Elani ◽  
Sowmya Purushothaman ◽  
Paula J. Booth ◽  
John M. Seddon ◽  
Nicholas J. Brooks ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Lipid Bilayer ◽  
Lipid Bilayers ◽  
Asymmetric Membranes ◽  
Membrane Asymmetry

We detail an approach for constructing asymmetric membranes and characterising their mechanical properties, leading to the first measurement of the effect of asymmetry on lipid bilayer mechanics.

scholarly journals Lipid flip-flop and desorption from supported lipid bilayers is independent of curvature

PLoS ONE ◽  
2020 ◽  
Vol 15 (12) ◽  
pp. e0244460
Author(s):  
Haoyuan Jing ◽  
Yanbin Wang ◽  
Parth Rakesh Desai ◽  
Kumaran S. Ramamurthi ◽  
Siddhartha Das
Keyword(s):  
Lipid Bilayer ◽  
Lipid Bilayers ◽  
Md Simulations ◽  
Packing Fraction ◽  
Membrane Curvature ◽  
Supported Lipid Bilayer ◽  
Flip Flop ◽  
Lipid Molecule ◽  
Membrane Asymmetry ◽  
Cell Shapes

Flip-flop of lipids of the lipid bilayer (LBL) constituting the plasma membrane (PM) plays a crucial role in a myriad of events ranging from cellular signaling and regulation of cell shapes to cell homeostasis, membrane asymmetry, phagocytosis, and cell apoptosis. While extensive research has been conducted to probe the lipid flip flop of planar lipid bilayers (LBLs), less is known regarding lipid flip-flop for highly curved, nanoscopic LBL systems despite the vast importance of membrane curvature in defining the morphology of cells and organelles and in maintaining a variety of cellular functions, enabling trafficking, and recruiting and localizing shape-responsive proteins. In this paper, we conduct molecular dynamics (MD) simulations to study the energetics, structure, and configuration of a lipid molecule undergoing flip-flop and desorption in a highly curved LBL, represented as a nanoparticle-supported lipid bilayer (NPSLBL) system. We compare our findings against those of a planar substrate supported lipid bilayer (PSSLBL). Our MD simulation results reveal that despite the vast differences in the curvature and other curvature-dictated properties (e.g., lipid packing fraction, difference in the number of lipids between inner and outer leaflets, etc.) between the NPSLBL and the PSSLBL, the energetics of lipid flip-flop and lipid desorption as well as the configuration of the lipid molecule undergoing lipid flip-flop are very similar for the NPSLBL and the PSSLBL. In other words, our results establish that the curvature of the LBL plays an insignificant role in lipid flip-flop and desorption.

scholarly journals In situ, fluorescence lifetime-based measurements of cell membrane micromechanics

2019 ◽  
Author(s):  
S Son ◽  
HS Muddana ◽  
C Huang ◽  
S Zhang ◽  
PJ Butler
Keyword(s):  
Mechanical Properties ◽  
Lipid Bilayer ◽  
Lipid Bilayers ◽  
Fluorescence Lifetime ◽  
Molecular Rotor ◽  
Cell Deformability ◽  
Lifetime Distributions ◽  
Human Red Blood Cells ◽  
Area Per Lipid

ABSTRACTMicroscopic in situ measurements of the mechanical properties of lipid bilayers were derived from the mean and variance of the fluorescence lifetime distributions of 1’-dioctadecyl-3,3,3’3’-tetramethylindocarbocyanine perchlorate (DiI). In this method, DiI, incorporated into membranes, acts as a membrane-targeted molecular rotor whose fluorescence lifetime is sensitive to local lipid viscosity. A new model was developed in which changes in area per lipid were derived from the first and second moments of a stretched exponential distribution of fluorescence lifetimes of DiI, which were subsequently used to compute mean area per lipid and its variance, quantities directly related to bilayer compressibility and bending moduli. This method enabled molecular scale assays of surface micromechanics of membrane-bound entities, such as nanoliposomes and human red blood cells.STATEMENT OF SIGNIFICANCEDespite the progress in cell deformability studies, and in understanding mechanical properties of purified lipid bilayers, there has not, to date, been a method to measure the mechanics of the lipid bilayer in cells in situ. The current manuscript describes such a method. Using a fluorescent molecular rotor, DiI, embedded in the membrane, along with time resolved fluorescence, we directly measure area per lipid, and its temporal and spatial variance, properties directly related to bilayer mechanical moduli. Such a method will allow investigators to start exploring the relationship between lipid bilayer mechanics and cellular health and disease.

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.

scholarly journals The effect of polydispersity, shape fluctuations and curvature on small unilamellar vesicle small-angle X-ray scattering curves

2021 ◽  
Vol 54 (2) ◽  
pp. 557-568
Author(s):  
Veronica Chappa ◽  
Yuliya Smirnova ◽  
Karlo Komorowski ◽  
Marcus Müller ◽  
Tim Salditt
Keyword(s):  
Lipid Bilayer ◽  
Density Profile ◽  
Small Angle ◽  
Thermal Fluctuations ◽  
Electron Density Profile ◽  
Membrane Asymmetry ◽  
X Ray ◽  
X Ray Scattering ◽  
Vesicle Shape ◽  
Small Unilamellar Vesicles

Small unilamellar vesicles (20–100 nm diameter) are model systems for strongly curved lipid membranes, in particular for cell organelles. Routinely, small-angle X-ray scattering (SAXS) is employed to study their size and electron-density profile (EDP). Current SAXS analysis of small unilamellar vesicles (SUVs) often employs a factorization into the structure factor (vesicle shape) and the form factor (lipid bilayer electron-density profile) and invokes additional idealizations: (i) an effective polydispersity distribution of vesicle radii, (ii) a spherical vesicle shape and (iii) an approximate account of membrane asymmetry, a feature particularly relevant for strongly curved membranes. These idealizations do not account for thermal shape fluctuations and also break down for strong salt- or protein-induced deformations, as well as vesicle adhesion and fusion, which complicate the analysis of the lipid bilayer structure. Presented here are simulations of SAXS curves of SUVs with experimentally relevant size, shape and EDPs of the curved bilayer, inferred from coarse-grained simulations and elasticity considerations, to quantify the effects of size polydispersity, thermal fluctuations of the SUV shape and membrane asymmetry. It is observed that the factorization approximation of the scattering intensity holds even for small vesicle radii (∼30 nm). However, the simulations show that, for very small vesicles, a curvature-induced asymmetry arises in the EDP, with sizeable effects on the SAXS curve. It is also demonstrated that thermal fluctuations in shape and the size polydispersity have distinguishable signatures in the SAXS intensity. Polydispersity gives rise to low-q features, whereas thermal fluctuations predominantly affect the scattering at larger q, related to membrane bending rigidity. Finally, it is shown that simulation of fluctuating vesicle ensembles can be used for analysis of experimental SAXS curves.

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.

scholarly journals Variation of thermal conductivity of DPPC lipid bilayer membranes around the phase transition temperature

2017 ◽  
Vol 14 (130) ◽  
pp. 20170127 ◽  
Author(s):  
Sina Youssefian ◽  
Nima Rahbar ◽  
Christopher R. Lambert ◽  
Steven Van Dessel
Keyword(s):  
Phase Transition ◽  
Thermal Conductivity ◽  
Thermal Properties ◽  
Transition Temperature ◽  
Lipid Bilayer ◽  
Lipid Bilayers ◽  
Phase Transition Temperature ◽  
Temperature Gradients ◽  
Phase Behaviour ◽  
Gel Phase

Given their amphiphilic nature and chemical structure, phospholipids exhibit a strong thermotropic and lyotropic phase behaviour in an aqueous environment. Around the phase transition temperature, phospholipids transform from a gel-like state to a fluid crystalline structure. In this transition, many key characteristics of the lipid bilayers such as structure and thermal properties alter. In this study, we employed atomistic simulation techniques to study the structure and underlying mechanisms of heat transfer in dipalmitoylphosphatidylcholine (DPPC) lipid bilayers around the fluid–gel phase transformation. To investigate this phenomenon, we performed non-equilibrium molecular dynamics simulations for a range of different temperature gradients. The results show that the thermal properties of the DPPC bilayer are highly dependent on the temperature gradient. Higher temperature gradients cause an increase in the thermal conductivity of the DPPC lipid bilayer. We also found that the thermal conductivity of DPPC is lowest at the transition temperature whereby one lipid leaflet is in the gel phase and the other is in the liquid crystalline phase. This is essentially related to a growth in thermal resistance between the two leaflets of lipid at the transition temperature. These results provide significant new insights into developing new thermal insulation for engineering applications.

scholarly journals Structure of the DMPC lipid bilayer ripple phase

Soft Matter ◽  
2015 ◽  
Vol 11 (5) ◽  
pp. 918-926 ◽  
Author(s):  
Kiyotaka Akabori ◽  
John F. Nagle
Keyword(s):  
High Resolution ◽  
Lipid Bilayer ◽  
Lipid Bilayers ◽  
X Ray ◽  
Ripple Phase

High resolution X-ray study provides new insight for the enigmatic ripple phase in lipid bilayers.

Maturation of the scolex syncytium in the metacestode ofHymenolepis diminuta, with special reference to microthrix formation

Parasitology ◽  
1984 ◽  
Vol 88 (2) ◽  
pp. 341-349 ◽  
Author(s):  
K. Sylvia Richards ◽  
C. Arme
Keyword(s):  
Developmental Stages ◽  
Apical Membrane ◽  
Final Host ◽  
Hymenolepis Diminuta ◽  
Bearing Surface ◽  
Adult Type ◽  
Asymmetric Membranes ◽  
Membrane Asymmetry ◽  
Outer Leaflet ◽  
Early Developmental

SUMMARYThe entire surface of the early developmental stages of the cysticercoid ofHymenolepis diminutabears microvilli. Posteriad differentiation produces a microthrix-bearing surface on the presumptive scolex region, commencing before scolex retraction in cysticercoids inTenebrio molitorkept at 26°C. During sucker development, the scolex syncytial cytoplasm possesses electron-dense discoidal bodies, aligned parallel to the surface. They become associated with the apical membrane, domes are formed and electron-dense spine-like profiles become apparent. Elevation on short shafts follows, and multilaminate baseplates are then discernible. Fewer microvilli are now present and vesicles with asymmetric membranes (denser inner leaflet) occur within the syncytial cytoplasm. Before scolex retraction, this differentiation extends to the level of the suckers; thus the neck, which becomes reflected on retraction, still possesses only microvilli. After retraction, differentiation proceeds rapidly with increased growth of existing microtriches, discoidal bodies possibly contributing to the shaft support material; the reflected neck develops microtriches and the microvilli are shed into the scolex retraction cavity. The ‘asymmetric’ vesicles increase numerically, some fusing with the apical membrane and releasing their contents. Concurrently, apical membrane asymmetry (denser outer leaflet) becomes apparent. The adult-type surface is formed by 3 days post-scolex retraction, coinciding with the earliest time that the metacestode is infective to the final host.

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