Biomimetic Microdroplet Membrane Interface: Detection of the Lateral Localization of Amyloid Beta Peptides

Lateral membrane organization into domains, such as lipid rafts, plays an important role in the selective association of biological and nonbiological materials on heterogeneous membrane surfaces. The localization of such materials has profound influence on cellular responses. We constructed a biomimetic water-in-oil microdroplet membrane to study the lateral localization of these materials at heterogeneous biological interfaces. As a case study, we studied selective association of amyloid β peptide on the constructed membrane surface. Amyloid β peptide has attracted much attention as one of these membrane-associating proteins because of its “role” in Alzheimer’s disease pathology. Ternary lipid membranes covering microdroplets successfully produced lipid ordered structures, which mimicked biological lipid rafts. We revealed that amyloid β peptide selectively localizes within nonraft fluid membrane regions. The successful lateral organization in microdroplet membrane systems may lead to new opportunities for the study of molecular associations within heterogeneous membranes

Physicochemical Profiling of Surfactant-Induced Membrane Dynamics in a Cell-Sized Liposome

We used a cell-sized model system, giant liposomes, to investigate the interaction between lipid membranes and surfactants, and the membrane transformation during the solubilization process was captured in real time. We found that there are four distinct dynamics in surfactant-induced membrane deformation: an episodic increase in the membrane area prior to pore-forming associated shrinkage (Dynamics A), fission into many small liposomes (Dynamics B), the formation of multilamellar vesicles and peeling (Dynamics C), and bursting (Dynamics D). Classification of the diversity of membrane dynamics may contribute to a better understanding of the physicochemical mechanism of membrane solubilization induced by various surfactants

Size-Dependent Partitioning of Nano/Microparticles Mediated by Membrane Lateral Heterogeneity

It is important that we understand the physical, chemical, and biological mechanisms that govern the interaction between nanoparticles (NPs) and heterogeneous cellular surfaces because of the possible cytotoxicity of engineered nanomaterials. In this study, we investigated the lateral localization of nano/microparticles within a biomimetic heterogeneous membrane interface using cell-sized two-phase liposomes. We found that lateral heterogeneity in the membrane mediates the partitioning of nano/microparticles in a size-dependent manner: small particles with a diameter of ≤200 nm were localized in an ordered phase, whereas large particles preferred a fluidic disordered phase. This partitioning behavior was verified by temperature-controlled membrane miscibility transition and laser-trapping of associated particles. In terms of the membrane elastic energy, we present a physical model that explains this localization preference of nano/microparticles. The calculated threshold diameter of particles that separates the particle-partitioning phase was 260 nm, which is in close agreement with our observation (200 nm). These findings may lead to a better understanding of the basic mechanisms that underlie the association of nanomaterials within a cell surface

Ion Permeation by a Folded Multiblock Amphiphilic Oligomer Achieved by Hierarchical Construction of Self-Assembled Nanopores

A multiblock amphiphilic molecule <b>1</b>, with a tetrameric alternating sequence of hydrophilic and hydrophobic units, adopts a folded structure in a liposomal membrane like a multipass transmembrane protein, and is able to transport alkali metal cations through the membrane. Hill’s analysis and conductance measurements, analyzed by the Hille equation, revealed that the tetrameric assembly of <b>1</b> forms a 0.53 nm channel allowing for permeation of cations. Since neither <b>3</b>, bearing flexible hydrophobic units and forming no stacked structures in the membrane, nor <b>2</b>, a monomeric version of <b>1</b>, is able to transport cations, the folded conformation of <b>1</b> in the membrane is likely essential for realizing its function. Thus, function and hierarchically formed higher-order structures of <b>1</b>, is strongly correlated with each other like proteins and other biological macromolecules

Micrometer-Size Vesicle Formation Triggered by UV Light

Vesicle formation is a fundamental kinetic process related to the vesicle budding and endocytosis in a cell. In the vesicle formation by artificial means, transformation of lamellar lipid aggregates into spherical architectures is a key process and known to be prompted by e.g. heat, infrared irradiation, and alternating electric field induction. Here we report UV-light-driven formation of vesicles from particles consisting of crumpled phospholipid multilayer membranes involving a photoactive amphiphilic compound composed of 1,4-bis­(4-phenylethynyl)­benzene (BPEB) units. The particles can readily be prepared from a mixture of these components, which is casted on the glass surface followed by addition of water under ultrasonic radiation. Interestingly, upon irradiation with UV light, micrometer-size vesicles were generated from the particles. Neither infrared light irradiation nor heating prompted the vesicle formation. Taking advantage of the benefits of light, we successfully demonstrated micrometer-scale spatiotemporal control of single vesicle formation. It is also revealed that the BPEB units in the amphiphile are essential for this phenomenon