Strategies in the reassembly of membrane proteins into lipid bilayer systems and their functional assay

The effects of lipids and surfactants on TLR5-proteoliposome functionality for flagellin detection using surface plasmon resonance biosensing

The use of proteoliposomes as affinity elements in conjunction with a surface plasmon resonance sensor is a high-sensitivity alternative for the detection of multiple analytes. However, one of the most important aspects of these conformations is maintaining the functionality of the immobilized protein, which is determined by the choice of lipids and surfactants employed in the reconstitutions. Previously, we demonstrated the functionality of TLR5-proteoliposomes as screening affinity elements of bacterial flagellin. In this new study we change the conditions of immobilization of TLR5 and evaluate how the fluidity of the membrane and the final size of the liposomes affect the functionality of the construct and thus increase their utility as an affinity element for design of new biosensors. In particular, we used reconstructions into preformed liposomes composed of the lipids POPC, POPC-DMPC and POPC-POPE mediated by the use of surfactants OG, Triton X100, and DDM, respectively. The affinity results were evaluated by SPR technology proteoliposomes and were correlated with the anisotropic change in the membrane status; the final sizes of the proteoliposomes were estimated. Our results clearly show the dependence of fluidity and final size of the proteoliposomes with surface plasmon resonance affinity measurements.

Nanotechnology with s-layer proteins

Nanosciences are distinguished by the cross-fertilization of biology, chemistry, material sciences, and solid-state physics and hence open up a great variety of new opportunities for innovation. The technological utilization of self-assembly systems, wherein molecules spontaneously associate under equilibrium conditions into reproducible supramolecular aggregates, is one key challenge in nanosciences for life and nonlife science applications. The attractiveness of such processes is due to their ability to build uniform, ultrasmall functional units and the possibility to exploit such structures at meso- and macroscopic scale very frequently by newly developed techniques and methods. By the utilization of crystalline bacterial cell-surface proteins (S-layer proteins) innovative approaches for the assembly of supramolecular structures and devices with dimensions of a few to tens of nanometers have been developed. S-layers have proven to be particularly suited as building blocks in a molecular construction kit involving all major classes of biological molecules. The controlled immobilization of biomolecules in an ordered fashion on solid substrates and their controlled confinement in definite areas of nanometer dimensions are key requirements for many applications including the development of bioanalytical sensors, biochips, molecular electronics, biocompatible surfaces, and signal processing between functional membranes, cells, and integrated circuits.

S-layer-supported lipid membranes

Many prokaryotic organisms (archaea and bacteria) are covered by a regularly ordered surface layer (S-layer) as the outermost cell wall component. S-layers are built up of a single protein or glycoprotein species and represent the simplest biological membrane developed during evolution. Pores in S-layers are of regular size and morphology, and functional groups on the protein lattice are aligned in well-defined positions and orientations. Due to the high degree of structural regularity S-layers represent unique systems for studying the structure, morphogenesis, and function of layered supramolecular assemblies. Isolated S-layer subunits of numerous organisms are able to assemble into monomolecular arrays either in suspension, at air/water interfaces, on planar mono- and bilayer lipid films, on liposomes and on solid supports (e.g. silicon wafers). Detailed studies on composite S-layer/lipid structures have been performed with Langmuir films, freestanding bilayer lipid membranes, solid supported lipid membranes, and liposomes. Lipid molecules in planar films and liposomes interact via their head groups with defined domains on the S-layer lattice. Electrostatic interactions are the most prevalent forces. The hydrophobic chains of the lipid monolayers are almost unaffected by the attachment of the S-layer and no impact on the hydrophobic thickness of the membranes has been observed. Upon crystallization of a coherent S-layer lattice on planar and vesicular lipid membranes, an increase in molecular order is observed, which is reflected in a decrease of the membrane tension and an enhanced mobility of probe molecules within an S-layer-supported bilayer. Thus, the terminology 'semifluid membrane' has been introduced for describing S-layer-supported lipid membranes. The most important feature of composite S-layer/lipid membranes is an enhanced stability in comparison to unsupported membranes.

Surface-bound biomembranes incorporating receptors: electrochemical and structural characterization

A generic method is described for forming surface-bound structures that incorporate protein receptors in a membrane-like environment. Silane reagents (octadecyltrichlorosilane and dimethyloctadecylchlorosilane) were used to produce primed substrates bearing full and partial monolayers, respectively. Biomembranes were formed by dialysis of detergent-solubilized membranes in the presence of two different alkylsilanized substrates: Si/SiO2 electrodes and glass microspheres. Electrochemical analysis of the capacitance was used to determine apparent thickness and degree of surface coverage at each stage in the deposition process. Elemental analysis on glass beads gave the hydrocarbon incorporation. Glass bead substrates were also examined by Fourier transform infrared spectroscopy to evaluate the alkylsilanized substrate before and after dialysis. Both vertebrate rhodopsin and the nicotinic acetylcholine receptor could be incorporated into structures with composition and dimensions similar to natural bilayer membranes. The techniques reported here are applicable for coupling membrane receptors to a variety of transducing substrates used in biosensors.

Micellar enzymology

Experimental approaches to modelling the enzymatic function of biological membranes are discussed. Emphasis is given to pseudohomogeneous systems such as proteolipid complexes and enzymes in organic solvents; the latter are solubilized with phospholipids or synthetic surfactants. Methods for producing and studying such micellar systems are considered. The key research problems of micellar enzymology are formulated and its relation to enzyme membranology is discussed. Finally, the new potentialities are noted of applied enzymology (biotechnology) offered by application of a colloidal solution of water in organic solvents as a microheterogeneous medium for enzymatic reactions.

Excitable cell made of thermal proteinoids

Such phenomena as electrical polarization across the membrane, electrical discharges, current-voltage characteristics, negative resistance and some light characteristics are described for synthetic cells made of thermal proteinoids. The thermal proteinoid cell is considered as a structural and functional model of the excitable natural cell.