Reorganization of Ternary Lipid Mixtures of Non-Phosphorylated Phosphatidylinositol Interacting with Angiomotin

Phosphatidylinositol (PI) lipids are necessary for many cellular signaling pathways of membrane associated proteins, such as Angiomotin (Amot). The Amot family regulates cellular polarity, growth, and migration. Given the low concentration of PI lipids in these membranes, it is likely that such protein-membrane interactions are stabilized by lipid domains or small lipid clusters. By small-angle x-ray scattering, we show that non-phosphorylated PI lipids induce lipid de-mixing in ternary mixtures of phosphatidylcholine (PC) and phosphatidylethanolamine (PE), likely due to preferential interactions between the head groups of PE and PI. These results were obtained in the presence of buffer containing concentrations of Tris, HEPES, NaCl, EDTA, DTT, and Benzamidine at pH 8.0 that in previous work showed an ability to cause PC to phase separate but are necessary to stabilize Amot for in vitro experimentation. Collectively, this provided a framework for determining the effect of Amot on lipid organization. Using fluorescence spectroscopy, we were able to show that the association of Amot with this lipid platform causes significant reorganization of the lipid into a more homogenous organization. This reorganization mechanism could be the basis for Amot membrane association and fusigenic activity previously described in the literature and should be taken into consideration in future protein-membrane interaction studies

Electrochemical Activity of Glucose Oxidase on a Poly(ionic liquid)–Au Nanoparticle Composite

Glucose oxidase (GOx) adsorbed on an ionic liquid-derived polymer containing internally organized columns of Au nanoparticles exhibits direct electron transfer and bioelectrocatalytic properties towards the oxidation of glucose. The cationic poly­(ionic liquid) provides an ideal substrate for the electrostatic immobilization of GOx. The encapsulated Au nanoparticles serve to both promote the direct electron transfer with the recessed enzyme redox centers and impart electronic conduction to the composite, allowing it to function as an electrode for electrochemical detection

Reversible Lifting of Surface Supported Lipid Bilayers with a Membrane-Spanning Nonionic Triblock Copolymer

Neutron reflectometry was used to monitor structural variations in surface-supported dimyristoylphosphatidycholine (DMPC) bilayers induced by the addition of Triton X-100, a surfactant commonly used to aid solubilization of membrane proteins, and the coaddition of a membrane spanning nonionic amphiphilic triblock copolymer, (PEO₁₁₇–PPO₄₇–PEO₁₁₇, Pluronic F98). Surfactant addition causes slight compression of the bilayer thickness and the creation of a distinct EO layer that increases the hydrophilic layer proximal to the supporting substrate (i.e., a water and EO gap between the lipid bilayer and quartz) to 6.8 ± 0.4 Å. Addition of the triblock copolymer into the DMPC:Triton X-100 bilayer increases the complexity of (broadens) the lipid phase transition, further compresses the bilayer, and continues to expand the proximal hydrophilic layer thickness. The observed structural changes are temperature dependent with transmembrane polymer insertion achieved at 37 °C, leading to a compressed membrane thickness of 39.2 ± 0.2 Å and proximal gap of 45.0 ± 0.2 Å. Temperature-driven exclusion of the polymer at 15 °C causes partitioning of the polymer into the proximal space generating a large hydrogel cushion 162 ± 16 Å thick. An intermediate gap width (10–27 Å) is achieved at room temperature (22–25 °C). The temperature-driven changes in the proximal hydrophilic gap dimensions are shown to be reversible, but thermal history causes variation in magnitude. Temperature-driven changes in polymer association with a supported lipid bilayer offer a facile means to reversibly control both the membrane characteristics as well as the separation between membrane and solid substrate