Unraveling the phase behavior, mechanical stability, and protein reconstitution properties of polymer-lipid hybrid vesicles

Hybrid vesicles consisting of natural phospholipids and synthetic amphiphilic copolymers have shown remarkable material properties and potential for biotechnology, combining the robustness of polymers with the biocompatibility of phospholipid membranes. To predict and optimize the mixing behavior of lipids and copolymers, as well as understand the interaction between the hybrid membrane and macromolecules like membrane proteins, a comprehensive understanding at the molecular level is essential. This can be achieved by a combination of molecular dynamics simulations and experiments. Here, simulations of POPC and PBD22-b-PEO14 hybrid membranes are shown, uncovering different copolymer configurations depending on the polymer-to-lipid ratio. High polymer concentrations created thicker membranes with an extended polymer conformation, while high lipid content led to the collapse of the polymer chain. High concentrations of polymer were further correlated with a decreased area compression modulus and altered lateral pressure profiles, hypothesized to result in the experimentally observed improvement in membrane protein reconstitution and resistance toward destabilization by detergents. Finally, simulations of a WALP peptide embedded in the bilayer showed that only membranes with up to 50% polymer content favored a transmembrane configuration. These simulations correlate with previous and new experimental results and provide a deeper understanding of the properties of lipid-copolymer hybrid membranes

Durable vesicles for reconstitution of membrane proteins in biotechnology

The application of membrane proteins in biotechnology requires robust, durable reconstitution systems that enhance their stability and support their functionality in a range of working environments. Vesicular architectures are highly desirable to provide the compartmentalisation to utilise the functional transmembrane transport and signalling properties of membrane proteins. Proteoliposomes provide a native-like membrane environment to support membrane protein function, but can lack the required chemical and physical stability. Amphiphilic block copolymers can also self-assemble into polymersomes: tough vesicles with improved stability compared with liposomes. This review discusses the reconstitution of membrane proteins into polymersomes and the more recent development of hybrid vesicles, which blend the robust nature of block copolymers with the biofunctionality of lipids. These novel synthetic vesicles hold great promise for enabling membrane proteins within biotechnologies by supporting their enhanced in vitro performance and could also contribute to fundamental biochemical and biophysical research by improving the stability of membrane proteins that are challenging to work with

Time-resolved fluorescence microscopic data (traces) of individual lipid vesicles with proton transport activity.

This data is shared by the authors of the published papers shown below. It also contains additional data gathered after the publication of the paper in the Journal of Chemical Society. The dataset contains time-resolved fluorescence microscopic data (traces) of individual lipid vesicles. It is derived from image data in a method detailed in the two publications. The original image data is too large to share conveniently. The shared dataset is intended to be used with the MATLAB code that is also shared by the authors (DOI:10.5518/150). The data structure of the shared data is described in the file 'open_data_script.m'

Artificial photosynthesis: Hybrid systems

Oxidoreductases are promising catalysts for organic synthesis. To sustain their catalytic cycles they require efficient supply with redox equivalents. Today classical biomimetic approaches utilizing natural electron supply chains prevail but artificial regeneration approaches bear the promise of simpler and more robust reaction schemes. Utilizing visible light can accelerate such artificial electron transport chains and even enable thermodynamically unfeasible reactions such as the use of water as reductant. This contribution critically summarizes the current state of the art in photoredoxbiocatalysis (i.e. light-driven biocatalytic oxidation and reduction reactions).</p

A study of cytochrome bo(3) in a tethered bilayer lipid membrane

An assay has been developed in which the activity of an ubiquinol oxidase from Escherichia coli, cytochrome bo3 (cbo3), is determined as a function of the hydrophobic substrate ubiquinol-10 (UQ-10) in tethered bilayer lipid membranes (tBLMs). UQ-10 was added in situ, while the enzyme activity and the UQ-10 concentration in the membrane have been determined by cyclic voltammetry. Cbo3 is inhibited by UQ-10 at concentrations above 5–10 pmol/cm2, while product inhibition is absent. Cyclic voltammetry has also been used to characterise the effects of three inhibitors; cyanide, inhibiting oxygen reduction; 2-n-Heptyl-4-hydroxyquinoline N-oxide (HQNO), inhibiting the quinone oxidation and Zn(II), thought to block the proton channels required for oxygen reduction and proton pumping activity. The electrochemical behaviour of cbo3 inhibited with HQNO and Zn(II) is almost identical, suggesting that Zn(II) ions inhibit the enzyme reduction by quinol, rather than oxygen reduction. This suggests that at Zn(II) concentration below 50 µM the proton release of cbo3 is inhibited, but not the proton uptake required to reduce oxygen to water

MATLAB code for the analysis of proton transport activity in single liposomes.

The code is adapted from the code the authors used to generate the data published in the associated papers. Minor improvements and bug fix have been added since the publication in the Journal of the American Chemical Society. The shared code does not contain all the code the authors used, but forms the basis of the data analysis.  The code is for fitting the time-resolved data (traces) of individual lipid vesicles with the method detailed in the paper. The code for getting the traces from the imaging data is not shared because it is specifically designed for the experimental set-up, but has been described in detail in the paper. Similar functions are available in many other softwares

Electrodes modified with lipid membranes to study quinone oxidoreductases

Quinone oxidoreductases are a class of membrane enzymes that catalyse the oxidation or reduction of membrane-bound quinols/quinones. The conversion of quinone/quinol by these enzymes is difficult to study because of the hydrophobic nature of the enzymes and their substrates. We describe some biochemical properties of quinones and quinone oxidoreductases and then look in more detail at two model membranes that can be used to study quinone oxidoreductases in a native-like membrane environment with their native lipophilic quinone substrates. The results obtained with these model membranes are compared with classical enzyme assays that use water-soluble quinone analogues