Search Results (77)

Mitochondria play a central role in cellular bioenergetics. They contribute significantly to ATP production, which is essential for maintaining cells. They are also key mediators of various types of cell death, including apoptosis, necroptosis, and ferroptosis. Additionally, they are one of the main regulators of autophagy. This brief review focuses on BID, a molecule of the BCL-2 family that is often overlooked. The importance of the cardiolipin/caspase-8/BID-FL platform, which is located on the surface of the outer mitochondrial membrane and generates tBID, will be emphasized. tBID is responsible for BAX/BAK delocalization and oligomerization, as well as the transmission of death signals. New insights into the regulation of caspase-8 and BID have emerged, and this review will highlight their originality in the context of activation and function. The focus will be on results from biophysical studies of artificial membranes, such as lipid-supported monolayers and giant unilamellar vesicles containing cardiolipin. We will present the destabilization of mitochondrial bioenergetics caused by the insertion of tBID at the mitochondrial contact site, as well as the marginal but additive role of the MTCH2 protein, not forgetting the new players. Full article

Background/Objectives: Army Liposome Formulation with QS21 (ALFQ) is a vaccine adjuvant formulation consisting of liposomes that contain saturated zwitterionic and anionic phospholipids, 55 mol% cholesterol, and small molar amounts of monophosphoryl lipid A (MPLA) and QS21 saponin as adjuvants. A unique aspect of ALFQ is that after addition of QS21 to nanoliposomes (<100 nm), the liposomes self-assemble through fusion to form giant (≥1000 nm) unilamellar vesicles (GUVs). The purpose of this study was to introduce and investigate new intermediate structures in the fusion process that we term tethered incomplete microspheres (TIMs), which were discovered by us incidentally as structures that were visible by phase contrast microscopy. Methods: Differential centrifugation; phase contrast microscopy; confocal microscopy of vesicles or TIMs which contain fluorescent chromophores linked to phospholipids or cholesterol; ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) analysis of lipid components of liposomes and TIMs; and dynamic light scattering were all used for the characterization of TIMS. Results and Conclusions: (A) Sizes of TIMs range from overall aggregated structural sizes of ~1 µm to mega sizes of ≥200 µm. (B) Stable TIM structures occur when a fusion process is stopped by depletion of a fusogenic lipid during an evolving fusing of a lipid bilayer membrane. (C) TIMs consist of long-term stable (>2 years), but also metastable, tightly aggregated tear-drop or spherical incomplete GUVs tethered to visible masses of underlying vesicles that are not individually visible. (D) The TIMs and GUVs all contain phospholipid and cholesterol (when present) as bulk lipids. (E) Lyophilized liposomes lacking QS21 saponin, but which still contain MPLA (ALF55lyo), also self-assemble to form GUVs and TIMs. (F) Cholesterol is a required component in nanoliposomes for generation of GUVs and TIMs by addition of QS21. (G) Cholesterol is not required for production of GUVs and TIMs in ALFlyo, but cholesterol greatly reduces and narrows the polydisperse vesicle distribution. Full article

Antimicrobial peptides (AMPs) are a primary defense against pathogens. Here, we examined the interaction of two BP100 analogs, R²R⁵-BP100 (where Arg substitutes Lys 2 and 5) and R²R⁵-BP100-A-NH-C₁₆ (where an Ala and a C₁₆ hydrocarbon chain are added to the R²R⁵-BP100 C-terminus), with membrane models. Large unilamellar vesicles (LUVs) and giant unilamellar vesicles (GUVs) were prepared with the major lipids in Gram-positive (GP) and Gram-negative (GN) bacteria, as well as red blood cells (RBCs). Fluorescence data, dynamic light scattering (DLS), and zeta potential measurements revealed that upon achieving electroneutrality through peptide binding, vesicle aggregation occurred. Circular dichroism (CD) spectra corroborated these observations, and upon vesicle binding, the peptides acquired α-helical conformation. The peptide concentration, producing a 50% release of carboxyfluorescein (C₅₀) from LUVs, was similar for GP-LUVs. With GN and RBC-LUVs, C₅₀ decreased in the following order: BP100 > R²R⁵-BP100 > R²R⁵BP100-A-NH-C₁₆. Optical microscopy of GP-, GN-, and RBC-GUVs revealed the rupture or bursting of the two former membranes, consistent with a carpet mechanism of action. Using GUVs, we confirmed RBC aggregation by BP100 and R²R⁵-BP100. We determined the minimal inhibitory concentrations (MICs) of peptides for a GN bacterium (Escherichia coli (E. coli)) and two GP bacteria (two strains of Staphylococcus aureus (S. aureus) and one strain of Bacillus subtilis (B. subtilis)). The MICs for S. aureus were strain-dependent. These results demonstrate that Lys/Arg replacement can improve the parent peptide’s antimicrobial activity while increasing hydrophobicity renders the peptide less effective and more hemolytic. Full article

Fluorescent cholesterol probes are indispensable tools for studying membrane structure, dynamics, and trafficking. To better understand the structure–function relationship of fluorescent cholesteryl probes, we developed a series of five new modular naphthalimide-containing cholesteryl probes (CND15–CND19). These probes incorporate an L-lysine linker between the cholesterol moiety and the fluorophore, along with a series of distinct head groups. We conducted extensive biophysical characterizations of these probes, including the determination of their solvatochromic properties and lipid partitioning behavior using giant unilamellar vesicles. Molecular dynamics simulations were employed to identify key molecular interactions of these probes within model lipid membranes. Furthermore, live-cell imaging in 3T3 fibroblasts demonstrated the potential applications of these analogs in live-cell imaging, measuring cellular membrane dynamics and studying cholesterol-related processes. The results of this study underscore the critical role of the linker and head group in designing fluorescent cholesterol-mimicking probes. These findings provide valuable insights into optimizing probe designs for future cholesterol and membrane biology research. Full article

Drug carriers hold significant promise for precision medicine but face persistent challenges in balancing high encapsulation efficiency with structural preservation during active loading. In this study, we present a microelectromechanical system (MEMS)-driven platform that can generate gigahertz (GHz)-frequency acoustic streaming (1.55 GHz) to enable nondestructive, power-tunable drug encapsulation in lipid vesicles. Utilizing DSPE-PEG-modified bilayers with hydrodynamic shear forces, our method achieves transient membrane permeability that preserves membrane integrity while permitting controlled doxorubicin (DOX) influx. We developed the GHz acoustic MEMS platform and applied it to systematically investigate two drug loading strategies: (1) loading DOX into giant unilamellar vesicles (GUVs, >10 μm in diameter) prior to extrusion into small unilamellar vesicles (SUVs, 100 nm) versus (2) direct acoustic loading into pre-formed SUVs. The GUV-first approach demonstrated better performance, achieving 60.04% ± 1.55% encapsulation efficiency (EE%) at 250 mW acoustic power—a 5.93% enhancement over direct SUV loading (54.11% ± 0.72%). Structural analysis via TEM confirmed intact SUV morphology post-loading, while power-dependent EE% analysis showed a linear trend. This work bridges gaps in nanocarrier engineering by optimizing drug loading strategies, aiming to offer a potential drug carrier platform for drug delivery in biomedical treatment in future. Full article

In the last decades, numerous dendrimers with a variety of potential biomedical applications have been developed and investigated. The aim of the present study was to evaluate the molecular mechanisms of interaction between two dendrimers with proven antibacterial activity (4-N,N-dimethylamino-1,8-naphthalimide (Dab) and 3-bromo-Dab (Dab-Br)) and POPC (1-palmitoyl-2-oleoylphosphatidylcholine) model membranes (monolayers and liposomes). The pressure-area isotherms and the compressional modulus of the monolayers revealed that Dab is likely to penetrate the hydrophobic region of POPC, whereas Dab-Br inserts mainly into the lipid headgroup area. This assumption was confirmed by FTIR-ATR of POPC liposomes containing Dab and Dab-Br dendrimers. In addition, Dab induced a higher lipid order in POPC large unilamellar vesicles (LUVs) compared to Dab-Br. Moreover, both dendrimers changed the negative zeta potential of POPC vesicles to positive values, with slightly higher effect of Dab-Br, indicating electrostatic interactions between the lipid headgroups and dendrimers. Furthermore, Dab was able to reduce the average POPC LUVs’ size, unlike Dab-Br. The visualization of giant unilamellar vesicles revealed that the increasing dendrimer concentration induced model membrane shrinking and complete disintegration, which was more prominent for Dab. Based on the experimental results, new fundamental knowledge about the destabilizing effect of dendrimers on model lipid membranes will be acquired with a focus on their application in pharmacology and clinical practice. Full article

Giant unilamellar vesicles (GUVs) are versatile cell models in biomedical and environmental research. Of the various GUV production methods, hydrogel-assisted GUV production is most easily implemented in a typical biological laboratory. To date, agarose, polyvinyl alcohol, cross-linked dextran-PEG, polyacrylamide, and starch hydrogels have been used to produce GUVs. Some leach and contaminate the GUVs, while others require handling toxic material or specialised chemistry, thus limiting their use by novices. Alternative hydrogel materials could address these issues or even offer novel advantages. To facilitate discovery, we replaced the manual spreading of reagents with controlled drop-casting in glass Petri dishes and polystyrene multi-well plates, allowing us to rapidly screen up to 96 GUV-production formulations simultaneously. Exploiting this, we rapidly evaluated assorted biomedical hydrogels, including PEG-DA, cross-linked hyaluronic acid, Matrigel, and cross-linked DNA. All of these alternatives successfully produced GUVs. In the process, we also developed a treatment for recycling agarose and polyvinyl alcohol hydrogels for GUV production, and successfully encapsulated porcine liver esterase (PLE-GUVs). PLE-GUVs offer a novel method of GUV labelling and tracing, which emulates the calcein-AM staining behaviour of cells. Our results highlight the utility of our protocol for potentiating substrate material discovery, as well as protocol and product development. Full article

Giant unilamellar vesicles (GUVs) are frequently used as membrane models in studies of membrane properties. They are most often produced using the electroformation method. However, there are a number of parameters that can influence the success of the procedure. Some of the most common conditions that have been shown to have a negative effect on GUV electroformation are the presence of high cholesterol (Chol) concentrations, the use of mixtures containing charged lipids, and the solutions with an elevated ionic strength. High Chol concentrations are problematic for the traditional electroformation protocol as it involves the formation of a dry lipid film by complete evaporation of the organic solvent from the lipid mixture. During drying, anhydrous Chol crystals form. They are not involved in the formation of the lipid bilayer, resulting in a lower Chol concentration in the vesicle bilayer compared to the original lipid mixture. Motivated primarily by the issue of artifactual Chol demixing, we have modified the electroformation protocol by incorporating the techniques of rapid solvent exchange (RSE), ultrasonication, plasma cleaning, and spin-coating for reproducible production of GUVs from damp lipid films. Aside from decreasing Chol demixing, we have shown that the method can also be used to produce GUVs from lipid mixtures with charged lipids and in ionic solutions used as internal solutions. A high yield of GUVs was obtained for Chol/1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) samples with mixing ratios ranging from 0 to 2.5. We also succeeded in preparing GUVs from mixtures containing up to 60 mol% of the charged lipid 1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-L-serine (POPS) and in NaCl solutions with low ionic strength (<25 mM). Full article

The SARS-CoV-2 E protein is an enigmatic viral structural protein with reported viroporin activity associated with the acute respiratory symptoms of COVID-19, as well as the ability to deform cell membranes for viral budding. Like many viroporins, the E protein is thought to oligomerize with a well-defined stoichiometry. However, attempts to determine the structure of the protein complex have yielded inconclusive results, suggesting several possible oligomers, ranging from dimers to pentamers. Here, we combined patch-clamp, confocal fluorescence microscopy on giant unilamellar vesicles, and atomic force microscopy to show that E protein can exhibit two modes of membrane activity depending on membrane lipid composition. In the absence or the presence of a low content of cholesterol, the protein forms short-living transient pores, which are seen as semi-transmembrane defects in a membrane by atomic force microscopy. Approximately 30 mol% cholesterol is a threshold for the transition to the second mode of conductance, which could be a stable pentameric channel penetrating the entire lipid bilayer. Therefore, the E-protein has at least two different types of activity on membrane permeabilization, which are regulated by the amount of cholesterol in the membrane lipid composition and could be associated with different types of protein oligomers. Full article

The plasma membrane lipid distribution is asymmetric, with several anionic lipid species located in its inner leaflet. Among these, phosphatidylserine (PS) plays a crucial role in various important physiological functions. Over the last decade several methods have been developed that allow for the fabrication of large or giant unilamellar vesicles (GUVs) with an asymmetric lipid composition. Investigating the physicochemical properties of PS in such asymmetric lipid bilayers and studying its interactions with proteins necessitates the reliable fabrication of asymmetric GUVs (aGUVs) with a high degree of asymmetry that exhibit PS in the outer leaflet so that the interaction with peptides and proteins can be studied. Despite progress, achieving aGUVs with well-defined PS asymmetry remains challenging. Recently, a Ca²⁺-initiated hemifusion method has been introduced, utilizing the fusion of symmetric GUVs (sGUVs) with a supported lipid bilayer (SLB) for the fabrication of aGUVs. We extend this approach to create aGUVs with PS in the outer bilayer leaflet. Comparing the degree of asymmetry between aGUVs obtained via Ca²⁺ or Mg²⁺ initiated hemifusion of a phosphatidylcholine (PC) sGUVwith a PC/PS-supported lipid bilayer, we observe for both bivalent cations a significant number of aGUVs with near-complete asymmetry. The degree of asymmetry distribution is narrower for physiological salt conditions than at lower ionic strengths. While Ca²⁺ clusters PS in the SLB, macroscopic domain formation is absent in the presence of Mg²⁺. However, the clustering of PS upon the addition of Ca²⁺ is apparently too slow to have a negative effect on the quality of the obtained aGUVs. We introduce a data filtering method to select aGUVs that are best suited for further investigation. Full article

Directed evolution is a powerful technique for creating biomolecules such as proteins and nucleic acids with tailor-made properties for therapeutic and industrial applications by mimicking the natural evolution processes in the laboratory. Droplet microfluidics improved classical directed evolution by enabling time-consuming and laborious steps in this iterative process to be performed within monodispersed droplets in a highly controlled and automated manner. Droplet microfluidic chips can generate, manipulate, and sort individual droplets at kilohertz rates in a user-defined microchannel geometry, allowing new strategies for high-throughput screening and evolution of biomolecules. In this review, we discuss directed evolution studies in which droplet-based microfluidic systems were used to screen and improve the functional properties of biomolecules. We provide a systematic overview of basic on-chip fluidic operations, including reagent mixing by merging continuous fluid streams and droplet pairs, reagent addition by picoinjection, droplet generation, droplet incubation in delay lines, chambers and hydrodynamic traps, and droplet sorting techniques. Various microfluidic strategies for directed evolution using single and multiple emulsions and biomimetic materials (giant lipid vesicles, microgels, and microcapsules) are highlighted. Completely cell-free microfluidic-assisted in vitro compartmentalization methods that eliminate the need to clone DNA into cells after each round of mutagenesis are also presented. Full article

Drug delivery systems play a pivotal role in targeted pharmaceutical transport and controlled release at specific sites. Liposomes, commonly used as drug carriers, constitute a fundamental part of these systems. Moreover, the drug–liposome model serves as a robust platform for investigating interaction processes at both cellular and molecular levels. To advance our understanding of drug carrier uptake mechanisms, we employed fluorescence lifetime imaging microscopy (FLIM) and fluorescence correlation spectroscopy (FCS), leveraging the unique benefits of two-photon (2P) excitation. Our approach utilized giant unilamellar vesicles (GUVs) as a simplified model system for cell membranes, labelled with the amphiphilic fluorescent dye 3,3′-dioctadecyloxa-carbocyanine (DiOC₁₈(3)). Additionally, large unilamellar vesicles (LUVs) functioned as a drug carrier system, incorporating the spectrally distinct fluorescent sulforhodamine 101 (SRh101) as a surrogate drug. The investigation emphasized the diverse interactions between GUVs and LUVs based on the charged lipids employed. We examined the exchange kinetics and structural alterations of liposome carriers during the uptake process. Our study underscores the significance of employing 2P excitation in conjunction with FLIM and FCS. This powerful combination offers a valuable methodological approach for studying liposome interactions, positioning them as an exceptionally versatile model system with a distinct technical advantage. Full article

Giant unilamellar vesicles (GUVs) are membrane models used to study membrane properties. Electroformation is one of the methods used to produce GUVs. During electroformation protocol, dry lipid film is formed. The drying of the lipid film induces the cholesterol (Chol) demixing artifact, in which Chol forms anhydrous crystals which do not participate in the formation of vesicles. This leads to a lower Chol concentration in the vesicle bilayers compared to the Chol concentration in the initial lipid solution. To address this problem, we propose a novel electroformation protocol that includes rapid solvent exchange (RSE), plasma cleaning, and spin-coating methods to produce GUVs. We tested the protocol, focusing on vesicles with a high Chol content using different spin-coating durations and vesicle type deposition. Additionally, we compared the novel protocol using completely dry lipid film. The optimal spin-coating duration for vesicles created from the phosphatidylcholine/Chol mixture was 30 s. Multilamellar vesicles (MLVs), large unilamellar vesicles (LUVs) obtained by the extrusion of MLVs through 100 nm membrane pores and LUVs obtained by extrusion of previously obtained LUVs through 50 nm membrane pores, were deposited on an electrode for 1.5/1 Chol/phosphatidylcholine (POPC) lipid mixture, and the results were compared. Electroformation using all three deposited vesicle types resulted in a high GUV yield, but the deposition of LUVs obtained by the extrusion of MLVs through 100 nm membrane pores provided the most reproducible results. Using the deposition of these LUVs, we produced high yield GUVs for six different Chol concentrations (from 0% to 71.4%). Using a protocol that included dry lipid film GUVs resulted in lower yields and induced the Chol demixing artifact, proving that the lipid film should never be subjected to drying when the Chol content is high. Full article

Tubulation is a common cellular process involving the formation of membrane tubes ranging from 50 nm to 1 µm in diameter. These tubes facilitate intercompartmental connections, material transport within cells and content exchange between cells. The high curvature of these tubes makes them specific targets for proteins that sense local geometry. In vitro, similar tubes have been created by pulling on the membranes of giant unilamellar vesicles. Optical tweezers and micromanipulation are typically used in these experiments, involving the manipulation of a GUV with a micropipette and a streptavidin-coated bead trapped in optical tweezers. The interaction forms streptavidin/biotin bonds, leading to tube formation. Here, we propose a cost-effective alternative using only micromanipulation techniques, replacing optical tweezers with a Biomembrane Force Probe (BFP). The BFP, employing a biotinylated erythrocyte as a nanospring, allows for the controlled measurement of forces ranging from 1 pN to 1 nN. The BFP has been widely used to study molecular interactions in cellular processes, extending beyond its original purpose. We outline the experimental setup, tube formation and characterization of tube dimensions and energetics, and discuss the advantages and limitations of this approach in studying membrane tubulation. Full article

In this work, we have synthesized copper nanoforms (Cu NFs) using ascorbic acid as a reducing agent and polyvinylpyrrolidone as a stabilizer. Elemental characterization using EDS has shown the nanostructure to be of high purity and compare well with commercially sourced nanoforms. SEM images of both Cu NFs show some agglomeration. The in-house NFs had a better even distribution and size of the nanostructures. The XRD peaks represented a face-centered cubic structure of Cu₂O. The commercially sourced Cu NFs were found to be a mixture of Cu and Cu₂O. Both forms had a crystalline structure. Using these two types of Cu NFs, an antimicrobial study against Colletotrichum gloeosporioides, a devastating plant pathogen, showed the in-house Cu NFs to be most effective at inhibiting growth of the pathogen. Interestingly, at low concentrations, both Cu NFs increased fungal growth, although the mycelia appeared thin and less dense than in the control. SEM macrographs showed that the in-house Cu NFs inhibited the fungus by flattening the mycelia and busting some of them. In contrast, the mycelia were short and appeared clustered when exposed to commercial Cu NFs. The difference in effect was related to the size and/or oxidation state of the Cu NFs. Furthermore, the fungus produced a defense mechanism in response to the NFs. The fungus produced melanin, with the degree of melanization directly corresponding to the concentration of the Cu NFs. Localization of aggregated Cu NFs could be clearly observed outside of the model membranes. The large agglomerates may only contribute indirectly by a hit-and-bounce-off effect, while small structures may adhere to the membrane surface and/or internalize. Spatio-temporal membrane dynamics were captured in real time. The dominant dynamics culminated into large fluctuations. Some of the large fluctuations resulted in vesicular transformation. The major transformation was exo-bud/exo-cytosis, which may be a way to excrete the foreign object (Cu NFs). Full article