Mimic Cell Membranes Research Articles

Insertion and Anchoring of HIV-1 Fusion Peptide into Complex Membrane Mimicking Human T-cell.

A fundamental understanding of how HIV-1 envelope (Env) protein facilitates fusion is still lacking. The HIV-1 fusion peptide, consisting of 15 to 22 residues, is the N-terminus of the gp41 subunit of the Env protein. Further, this peptide, a promising vaccine candidate, initiates viral entry into target cells by inserting and anchoring into human immune cells. The influence of membrane lipid reorganization and the conformational changes of the fusion peptide during the membrane insertion and anchoring processes, which can significantly affect HIV-1 cell entry, remains largely unexplored due to the limitations of experimental measurements. In this work, we investigate the insertion of the fusion peptide into an immune cell membrane mimic through multiscale molecular dynamics simulations. We mimic the native T-cell by constructing a 9-lipid asymmetric membrane, along with geometrical restraints accounting for insertion in the context of gp41. To account for the slow timescale of lipid mixing while enabling conformational changes, we implement a protocol to go back and forth between atomistic and coarse-grained simulations. Our study provides a molecular understanding of the interactions between the HIV-1 fusion peptide and the T-cell membrane, highlighting the importance of conformational flexibility of fusion peptides and local lipid reorganization in stabilizing the anchoring of gp41 into the targeted host membrane during the early events of HIV-1 cell entry. Importantly, we identify a motif within the fusion peptide critical for fusion that can be further manipulated in future immunological studies.

Emerging Lipid-based Carriers for Systematic Utilization in the Pharmaceutical and Biomedical Sciences: A Review.

Emerging lipid-based carriers are revolutionizing drug delivery in the pharmaceutical and biomedical sciences. These innovative carriers harness the unique properties of lipids to improve the solubility, stability, and targeted delivery of therapeutic agents, ushering in a new era of precision medicine. Lipid- based carriers, such as liposomes, lipid nanoparticles, and solid lipid nanoparticles, offer several advantages. They can encapsulate both hydrophilic and hydrophobic drugs, enabling the delivery of a wide range of compounds. Additionally, lipids are biocompatible and biodegradable, minimizing the risk of toxicity. Their ability to mimic cell membranes allows for enhanced cellular uptake and controlled release, optimizing drug efficacy while minimizing side effects. Furthermore, lipid-based carriers are ideal for delivering drugs to specific sites within the body. By modifying the lipid composition, surface charge, and size, researchers can tailor these carriers to target tumours, inflamed tissues, or specific cells, improving therapeutic outcomes and reducing systemic toxicity. In summary, emerging lipid-based carriers are poised to transform pharmaceutical and biomedical sciences by addressing critical challenges in drug delivery. These carriers enhance drug stability, bioavailability, and targeted delivery, offering the potential to revolutionize the treatment of various diseases and improve patient outcomes. As research in this field continues to advance, we can expect even more sophisticated lipid-based carrier systems to emerge, further expanding the possibilities for precision medicine. This review focuses on the contribution of lipid carriers in the pharmaceutical and biomedical sciences.

Exploring the synergistic effects of amoxicillin and methylene blue on unsaturated lipid structures: A study of Langmuir monolayers and giant unilamellar vesicles

The potentially toxic effects of emerging pollutant mixtures often deviate from the individual compound effects, presenting additive, synergistic, or agonistic interactions. This study delves into the complex world of emerging pollutants' mixtures, with a particular focus on their potential impact on unsaturated lipid DOPC (1,2-dioleoyl-sn-glycerol-3-phosphocholine) structured as both monolayers and bilayers, which are valuable tools for mimicking cell membranes. Specifically, we examine the effects of two common types of pollutants: antibiotics (amoxicillin) and dyes (methylene blue). Utilizing Langmuir monolayers, our research reveals a synergistic effect within the pollutant mixture, as evidenced by pressure-area isotherms and polarization-modulated infrared reflection absorption spectroscopy. We identify the specific chemical interactions contributing to this synergistic effect. Furthermore, through contrast phase microscopy experiments on giant unilamellar vesicles (bilayer system), we find that the individual pollutants and the mixture exhibit similar molecular effects on the bilayer, revealing that the molecular size is a key factor in the bilayer-mixture of pollutant interaction. This highlights the importance of considering molecular size in the interactions with bilayer systems. In summary, our research dissects the critical factors of chemical interactions and molecular size concerning the effects of pollutants on DOPC, serving as simplified models of cell membranes. This study underscores the significance of comprehending the molecular effects of emerging pollutants on human health and the development of models for exploring their intricate interactions with cell membranes.

Filamentous-Actin-Mimicking Nanoplatform for Enhanced Cytosolic Protein Delivery.

Despite the potential of protein therapeutics, the cytosolic delivery of proteins with high efficiency and bioactivity remains a significant challenge owing to exocytosis and lysosomal degradation after endocytosis. Therefore, it is important to develop a safe and efficient strategy to bypass endocytosis. Inspired by the extraordinary capability of filamentous-actin (F-actin) to promote cell membrane fusion, a cyanine dye assembly-containing nanoplatform mimicking the structure of natural F-actin is developed. The nanoplatform exhibits fast membrane fusion to cell membrane mimics and thus enters live cells through membrane fusion and bypasses endocytosis. Moreover, it is found to efficiently deliver protein cargos into live cells and quickly release them into the cytosol, leading to high protein cargo transfection efficiency and bioactivity. The nanoplatform also results in the superior inhibition of tumor cells when loaded with anti-tumor proteins. These results demonstrate that this fusogenic nanoplatform can be valuable for cytosolic protein delivery and tumor treatment.

Anti-fouling plus: Engineered stent coating with inflammation-regulation capability enables enhanced tissue healing

Coagulation, inflammation, and hyperplasia frequently restrict the effectiveness of cardiovascular stents. It is critical to modify stent surfaces to allow for in situ tissue healing. Interrelated coagulation and inflammation can impede endothelialization and are critical to the long-term performance of cardiovascular implants. This study proposes a relatively bio-inert “Anti-fouling plus” coating that is effective in anti-coagulation and anti-inflammation at the early stage of implantation and provides mild inflammatory responses during tissue remodeling process. The phosphorylcholine (PC)-based polymer PM(PCLA) is reacted onto a polydopamine-treated polylactic acid (PLA) surface. PC-based polymers that mimic cell membranes present remarkable antiinflammation and anticoagulation properties. The composite of epigallocatechin gallate (EGCG) and tempol is loaded on the PM(PCLA) coating to achieve “anti-fouling plus” which can mediate inflammatory responses by scavenging reactive oxygen species. In vitro hemocompatibility and cell tests demonstrate the effectiveness of coatings in inhibiting thrombus and inflammation. Interestingly, this study originally reveals a novel strategy that the anti-fouling plus coating can direct vascular tissue healing on stent via promoted endothelialization and mediated contractile smooth muscle cell phenotype by switching inflammatory cells to a pro-repair phenotype during tissue healing process, even if the coating is relatively bio-inert.

Polymeric Giant Unilamellar Vesicles with Integrated DNA‐Origami Nanopores: An Efficient Platform for Tuning Bioreaction Dynamics Through Controlled Molecular Diffusion

AbstractGiant unilamellar vesicles (GUVs) are microcompartments serving to confine reactions, allow signaling pathways, or design synthetic cells. Polymer GUVs are composed of copolymer membranes mimicking cell membranes, and present advantages over lipid‐based GUVs, such as higher mechanical stability and chemical versatility. Such microcompartments are essential for understanding reactions/signaling occurring in cells, which are difficult to study by in vivo approaches due to the cell's complexity. However, the lack of control over their production, stability, and membrane diffusion properties is still limiting their use for bio‐related applications. Here, polymer GUVs produced by microfluidics and permeabilized with DNA‐origami nanopores (DoNs) that present a high level of control over these essential properties are introduced. After systematic optimization of conditions, DoN‐GUVs reveal a narrow size distribution, allow for high encapsulation efficiencies, and are stable for weeks, protecting encapsulated biomolecules. The kinetics of diffusion of molecules through the GUV's membrane is tuned by insertion of DoNs with a controlled 3D‐ structure. DNA polymerase I, encapsulated as model for bioreactions, successfully produced DNA duplex strands with spatiotemporal control. DoN‐GUVs loaded with active molecules open new avenues in bioreactions, from the detection of biomolecules, over the tuning of molecular transport rates, to the investigation of cellular processes/signaling.

Tunable lipid-coated nanoporous silver sheet for characterization of protein-membrane interactions by surface-enhanced Raman scattering (SERS)

Membrane environments affect protein structures and functions through protein-membrane interactions in a wide range of important biological processes. To better study the effects from the lipid’s hydrophilic and hydrophobic interaction with protein on different membrane regions, we developed the lipid-coated nanoporous silver sheets to provide tunable supported lipid monolayer/bilayer environments for in situ surface-enhanced Raman vibrational spectroscopy (SERS) characterizations. Under the controllable surface pressure, lipid monolayer/bilayer was coated along the microscopic curved surface of nanoporous silver sheets to serve as a cell membrane mimic as well as a barrier to avoid protein denaturation while empowering the high SERS enhancements from the underlying metallic bases allowing detection sensitivity at low physiological concentrations. Moreover, we fine-tuned the lipid packing density and controlled the orientation of the deposited lipid bilayers and monolayers to directly monitor the protein structures upon interactions with various membrane parts/positions. Our results indicate that lysozyme adopted the α-helical structure in both hydrophilic and hydrophobic interaction with lipid membrane. Interestingly, alpha-synuclein folded into the α-helical structure on the negatively charged lipid heads, whereas the hydrophobic lipid tails induced the β-sheet structural conversion of alpha-synuclein originated from its unstructured monomers. These direct observations on protein hydrophilic and hydrophobic interaction with lipid membrane might provide profound insights into the formation of the β-sheet-containing alpha-synuclein oligomers for further membrane disruptions and amyloid genesis associated with Parkinson’s disease. Hence, with the controllability and tunability of lipid environments, our platform holds great promise for more general applications in investigating the influences from membranes and the correlative structures of proteins under both hydrophilic and hydrophobic effects.Graphical

Enzymatic Glyco-Modification of Synthetic Membrane Systems.

The present report assesses the capability of a soluble glycosyltransferase to modify glycolipids organized in two synthetic membrane systems that are attractive models to mimic cell membranes: giant unilamellar vesicles (GUVs) and supported lipid bilayers (SLBs). The objective was to synthesize the Gb3 antigen (Galα1,4Galβ1,4Glcβ-Cer), a cancer biomarker, at the surface of these membrane models. A soluble form of LgtC that adds a galactose residue from UDP-Gal to lactose-containing acceptors was selected. Although less efficient than with lactose, the ability of LgtC to utilize lactosyl-ceramide as an acceptor was demonstrated on GUVs and SLBs. The reaction was monitored using the B-subunit of Shiga toxin as Gb3-binding lectin. Quartz crystal microbalance with dissipation analysis showed that transient binding of LgtC at the membrane surface was sufficient for a productive conversion of LacCer to Gb3. Molecular dynamics simulations provided structural elements to help rationalize experimental data.

Force-sensing in Piezo ion channels.

In 2010, Piezo proteins were discovered, which has led to stunning progress in the elucidation of the molecular basis for mechanosensation. Piezo channels are mechanosensitive ion channels that locally curve the membrane into a dome shape. Membrane elasticity theory predicts that the curved shape of the Piezo dome deforms the surrounding lipid membrane into a membrane footprint, which may amplify Piezo's sensitivity to applied forces and explain the observed modulation of Piezo gating through the cytoskeleton. We directly test the membrane elasticity theory of Piezo's membrane footprint through cryo-electron tomography of lipid bilayer vesicles deformed by Piezo channels, finding quantitative agreement between observed and predicted membrane shapes, with no free parameters. On this basis, it becomes possible to deduce elastic properties of membrane proteins solely from membrane shape measurements. We thus derive a force-distortion relationship for the Piezo dome, from which we infer the Piezo dome's intrinsic radius of curvature and bending stiffness in free-standing lipid membranes mimicking cell membranes, and predict Piezo's gating curve, with no free parameters. Our results suggest that Piezo's intrinsic curvature, membrane footprint, small stiffness, and large area are the key properties of Piezo that give rise to low-threshold, high-sensitivity mechanical gating.

Cell-sized asymmetric phospholipid-amphiphilic protein vesicles with growth, fission, and molecule transportation

Lipid vesicles, which mimic cell membranes in structure and components, have been used to study the origin of life and artificial cell construction. A different approach to developing cell-mimicking systems focuses on the formation of protein- or polypeptide-based vesicles. However, micro-sized protein vesicles that are similar in membrane dynamics to the cell and that reconstitute membrane proteins are difficult to form. In this study, we generated cell-sized asymmetric phospholipid-amphiphilic protein (oleosin) vesicles that allow the reconstitution of membrane proteins and the growth and fission of vesicles. These vesicles are composed of a lipid membrane on the outer leaflet and an oleosin membrane on the inner leaflet. Further, we elucidated a mechanism for the growth and fission of cell-sized asymmetric phospholipid-oleosin vesicles by feeding phospholipid micelles. Our asymmetric phospholipid-oleosin vesicles with the advantages of the lipid leaflet and the protein leaflet will potentially promote understanding of biochemistry and synthetic biology.

A berberine induced disassembly towards zwitterionic surfactant as mimicking cell membrane for light-scattering sensing and logic devices

A label-free light-scattering sensor for berberine determination was developed based on Gemini zwitterionic surfactant as logic devices. Amphiphilic phosphodiesters quaternary ammonium nanoparticles (PQANPs) with bionic phosphate ester structure were selected as a model for mimicking cell membrane. PQANPs self-assembled and formed the micelle structure, emitting strong light-scattering signal. Interestingly, the addition of berberine induced remarkable decrease of light-scattering attribute to its interfering behavior of PQANPs aggregation. Disassembly of PQANPs could be triggered due to electrostatic interaction and hydrophobic force between PQANPs and berberine. The berberine attached to the PQANPs surface and generated nanocomposites, resulting in significant reduce of light-scattering signal. Hence, it generated a strong light-scattering signal variation according to the change of the concentration of target. Our proposed light-scattering on-off sensor could be applied for berberine detection with detection limit of 27 nM. Moreover, a logic gate system was constructed based on PQANPs sensor with berberine and the interfering substances as the inputs and the light-scattering intensity as an output, which could hold great potential application in future clinical diagnosis and drug analysis.

Probing the Separation Distance between Biological Nanoparticles and Cell Membrane Mimics Using Neutron Reflectometry with Sub-Nanometer Accuracy.

Nanoparticle interactions with cellular membranes are controlled by molecular recognition reactions and regulate a multitude of biological processes, including virus infections, biological nanoparticle-mediated cellular communication, and drug delivery applications. Aided by the design of various supported cell membrane mimics, multiple methods have been employed to investigate these types of interactions, revealing information on nanoparticle coverage, interaction kinetics, as well as binding strength; however, precise quantification of the separation distance across which these delicate interactions occur remains elusive. Here, we demonstrate that carefully designed neutron reflectometry (NR) experiments followed by an attentive selection and application of suitable theoretical models offer a means to quantify the distance separating biological nanoparticles from a supported lipid bilayer (SLB) with sub-nanometer precision. The distance between the nanoparticles and SLBs was tuned by exploiting either direct adsorption or specific binding using DNA tethers with different conformations, revealing separation distances of around 1, 3, and 7 nm with nanometric accuracy. We also show that NR provides precise information on nanoparticle coverage, size distribution, material composition, and potential structural changes in the underlying planar SLB induced upon nanoparticle binding. The precision with which these parameters could be quantified should pave an attractive path for investigations of the interactions between nanoparticles and interfaces at length scales and resolutions that were previously inaccessible. This thus makes it possible to, for example, gain an in-depth understanding of the molecular recognition reactions of inorganic and biological nanoparticles with cellular membranes.

Rapid pattern formation in model cell membranes when using an electron beam

Patterning of supported lipid bilayers (SLBs) is a fundamental tool for mimicking and modeling of biological membranes, but it still remains a challenge to achieve resetting and retriggering for the membrane-mediated processes of the patterned SLBs. This paper reports that indirect scanning of an electron beam (EB) enables repeatable patterning and remodeling of SLBs. By indirect scanning of the EB onto SLBs through a 100-nm-thick silicon nitride membrane, chemical and electrical effects of scattered electrons can be applied to lipid molecules in SLBs; application of these effects enables formation and annihilation of diffusion barriers in SLBs. Two-dimensional patterning of SLBs was demonstrated to be controllable by changing the electron dose of the EB and two phenomena were applied to realize repeatable wiping off and wetting of SLB patterns. Moreover, respreading of SLBs was determined as able to induce remodeling of a raft domain in phase-separated SLBs. The proposed method will lead to a prototyping tool for mimicking cell membranes to design interactions of cells and membrane proteins as well as SLB-based microchips.

Potassium Ion Dynamics Imaging through Supported Lipid Bilayers with Surface Plasmon Resonance Microscopy

We have developed an optical microscope based on surface plasmon resonance (SPR) to observe the dynamics of potassium ion (K+) concentrations. We formed a polyvinyl chloride (PVC) film containing ionophores that trap K+ on top of a gold film that excites surface plasmon. By measuring the attenuated total reflection spectra when injecting pure water or K+ solution on the fabricated substrate, we confirmed that the ionophore chelation reaction changed the PVC refractive index. Subsequently, we constructed a custom-made optical system for SPR imaging, mounted the substrate, and imaged the two-dimensional diffusion of K+ concentration changes when high concentrations of K+ solution were injected onto the substrate. In addition, we formed supported lipid bilayers on the substrate, mimicking cell membranes. Compared with the movie without lipid bilayer formation, that with supported lipid bilayers was confirmed to have taken longer time to increase the concentration due to its shielding effect of K+. Finally, we added K+ channels into the lipid bilayer membrane and visualized a K+ diffusion using the same procedure as that in the previous imaging experiment. We succeeded in observing the dynamics of K+ concentration change through the K+ channels inserted in the lipid bilayer. The addition of K+ channels weakened the shielding effect and shortened the time required for the K+ concentration to increase.

Influence of cytochrome P450 3A4 and membrane lipid composition on doxorubicin activity

Drug resistance is known to depend on the interactions with cell membranes and other molecules such as human cytochromes P450 (CYPs) which are anchored on the endoplasmic reticulum (ER) membrane and involved in the metabolism of anticancer drugs. In this study, we determined the influence from cytochrome P450 3A4 (CYP3A4) on the interaction between the drug doxorubicin (DOX) and Langmuir monolayers mimicking cell membranes. The lipid composition was varied by changing the relative concentrations of cholesterol (Chol), 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine (DPPE), and L-α-phosphatidylinositol (PI). Three compositions were studied in detail which represented a healthy cell membrane and cancerous cell membranes. DOX induced an expansion in the surface pressure isotherms for all monolayers, with stronger effect for the composition of cancerous cell with a high Chol content, thus confirming the relevance of lipid composition. This effect decreased considerably when CYP3A4 was incorporated with the formation of CYP3A4-DOX complexes, according to results from polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS) measurements. Taken together, these results support the hypothesis of CYP3A4 being involved in drug resistance, which may be exploited to design strategies to enhance chemotherapy efficacy.

Elastic properties and shape of the Piezo dome underlying its mechanosensory function

We show in the companion paper that the free membrane shape of lipid bilayer vesicles containing the mechanosensitive ion channel Piezo can be predicted, with no free parameters, from membrane elasticity theory together with measurements of the protein geometry and vesicle size [C. A. Haselwandter, Y. R. Guo, Z. Fu, R. MacKinnon, Proc. Natl. Acad. Sci. U.S.A., 10.1073/pnas.2208027119 (2022)]. Here we use these results to determine the force that the Piezo dome exerts on the free membrane and hence, that the free membrane exerts on the Piezo dome, for a range of vesicle sizes. From vesicle shape measurements alone, we thus obtain a force-distortion relationship for the Piezo dome, from which we deduce the Piezo dome's intrinsic radius of curvature, [Formula: see text] nm, and bending stiffness, [Formula: see text], in freestanding lipid bilayer membranes mimicking cell membranes. Applying these estimates to a spherical cap model of Piezo embedded in a lipid bilayer, we suggest that Piezo's intrinsic curvature, surrounding membrane footprint, small stiffness, and large area are the key properties of Piezo that give rise to low-threshold, high-sensitivity mechanical gating.

Role of Surface Tension in Microrobot Penetration in Membranes.

cell-membrane fusion using microrobots can be a useful technique for delivering bioactive compounds to cellular systems. The role of membrane curvature and lipid ordering in the cell membrane penetration process is well known. However, once the fusion into the cell membrane is already initiated, the fluid dynamics of microrobot penetration based on tension difference of the microrobot solution and membrane curvature at the fusion pore has not been explored yet. Here, we demonstrate how surface tension difference among merging interfaces plays role in microrobot droplet penetration into a liquid bath, mimicking cell membrane fusion. The maximum penetration of a microrobot droplet into a liquid bath depends on the positive difference of surface tension between the droplet and liquid bath, longitudinal curvature of the bridge region, and the size of the droplet.

Tailored Multivalent Targeting of Siglecs with Photosensitizing Liposome Nanocarriers.

The modification of surfaces with multiple ligands allows the formation of platforms for the study of multivalency in diverse processes. Herein we use this approach for the implementation of a photosensitizer (PS)‐nanocarrier system that binds efficiently to siglec‐10, a member of the CD33 family of siglecs (sialic acid (SA)‐binding immunoglobulin‐like lectins). In particular, a zinc phthalocyanine derivative bearing three SA moieties (PcSA) has been incorporated in the membrane of small unilamellar vesicles (SUVs), retaining its photophysical properties upon insertion into the SUV's membrane. The interaction of these biohybrid systems with human siglec‐10‐displaying supported lipid bilayers (SLBs) has shown the occurrence of weakly multivalent, superselective interactions between vesicle and SLB. The SLB therefore acts as an excellent cell membrane mimic, while the binding with PS‐loaded SUVs shows the potential for targeting siglec‐expressing cells with photosensitizing nanocarriers.

Tailored Multivalent Targeting of Siglecs with Photosensitizing Liposome Nanocarriers

AbstractThe modification of surfaces with multiple ligands allows the formation of platforms for the study of multivalency in diverse processes. Herein we use this approach for the implementation of a photosensitizer (PS)‐nanocarrier system that binds efficiently to siglec‐10, a member of the CD33 family of siglecs (sialic acid (SA)‐binding immunoglobulin‐like lectins). In particular, a zinc phthalocyanine derivative bearing three SA moieties (PcSA) has been incorporated in the membrane of small unilamellar vesicles (SUVs), retaining its photophysical properties upon insertion into the SUV's membrane. The interaction of these biohybrid systems with human siglec‐10‐displaying supported lipid bilayers (SLBs) has shown the occurrence of weakly multivalent, superselective interactions between vesicle and SLB. The SLB therefore acts as an excellent cell membrane mimic, while the binding with PS‐loaded SUVs shows the potential for targeting siglec‐expressing cells with photosensitizing nanocarriers.

Monosialotetrahexosylganglioside Promotes Early Aβ42 Oligomer Formation and Maintenance.

The aggregation of the amyloid beta (Aβ) peptide is associated with Alzheimer's disease (AD) pathogenesis. Cell membrane composition, especially monosialotetrahexosylganglioside (GM1), is known to promote the formation of Aβ fibrils, yet little is known about the roles of GM1 in the early steps of Aβ oligomer formation. Here, by using GM1-contained liposomes as a mimic of the neuronal cell membrane, we demonstrate that GM1 is a critical trigger of Aβ oligomerization and aggregation. We find that GM1 not only promotes the formation of Aβ fibrils but also facilitates the maintenance of Aβ42 oligomers on liposome membranes. We structurally characterize the Aβ42 oligomers formed on the membrane and find that GM1 captures Aβ by binding to its arginine-5 residue. To interrogate the mechanism of Aβ42 oligomer toxicity, we design a new liposome-based Ca2+-encapsulation assay and provide new evidence for the Aβ42 ion channel hypothesis. Finally, we determine the toxicity of Aβ42 oligomers formed on membranes. Overall, by uncovering the roles of GM1 in mediating early Aβ oligomer formation and maintenance, our work provides a novel direction for pharmaceutical research for AD.