Single-channel recordings of gramicidin at agarose-supported bilayer lipid membranes formed by the tip-dip and painting methods

Characterizing the Structure and Interactions of Model Lipid Membranes Using Electrophysiology

The cell membrane is a protective barrier whose configuration determines the exchange both between intracellular and extracellular regions and within the cell itself. Consequently, characterizing membrane properties and interactions is essential for advancements in topics such as limiting nanoparticle cytotoxicity. Characterization is often accomplished by recreating model membranes that approximate the structure of cellular membranes in a controlled environment, formed using self-assembly principles. The selected method for membrane creation influences the properties of the membrane assembly, including their response to electric fields used for characterizing transmembrane exchanges. When these self-assembled model membranes are combined with electrophysiology, it is possible to exploit their non-physiological mechanics to enable additional measurements of membrane interactions and phenomena. This review describes several common model membranes including liposomes, pore-spanning membranes, solid supported membranes, and emulsion-based membranes, emphasizing their varying structure due to the selected mode of production. Next, electrophysiology techniques that exploit these structures are discussed, including conductance measurements, electrowetting and electrocompression analysis, and electroimpedance spectroscopy. The focus of this review is linking each membrane assembly technique to the properties of the resulting membrane, discussing how these properties enable alternative electrophysiological approaches to measuring membrane characteristics and interactions.

Transmembrane Signaling with Lipid-Bilayer Assemblies as a Platform for Channel-Based Biosensing

Artificial and natural lipid membranes that elicit transmembrane signaling is are useful as a platform for channel-based biosensing. In this account we summarize our research on the design of transmembrane signaling associated with lipid bilayer membranes containing nanopore-forming compounds. Channel-forming compounds, such as receptor ion-channels, channel-forming peptides and synthetic channels, are embedded in planar and spherical bilayer lipid membranes to develop highly sensitive and selective biosensing methods for a variety of analytes. The membrane-bound receptor approach is useful for introducing receptor sites on both planar and spherical bilayer lipid membranes. Natural receptors in biomembranes are also used for designing of biosensing methods.

Pore-forming compounds as signal transduction elements for highly sensitive biosensing

Pore-forming compounds are attracting much attention due to the signal transduction ability for the development of highly sensitive biosensing. In this review, we describe an overview of the recent advances made by our group in the design of molecular sensing interfaces of spherical and planar lipid bilayers and natural bilayers. The potential uses of pore-forming compounds, such as gramicidin and MCM-41, in lipid bilayers and natural glutamate receptor channels in biomembrane are presented.

Free-standing lipid bilayers in silicon chips-membrane stabilization based on microfabricated apertures with a nanometer-scale smoothness

In the present study, we propose a method for preparing stable free-standing bilayer lipid membranes (BLMs). The BLMs were prepared in a microfabricated aperture with a smoothly tapered edge, which was prepared in a nanometer-thick Si(3)N(4) septum by the wet etching method. Owing to this structure, the stress on lipid bilayers at the contact with the septum was minimized, leading to remarkable membrane stability. The BLMs were not broken by applying a constant voltage of +/-1 V. The membrane lifetime was 15-45 h with and without an incorporated gramicidin channel. Gramicidin single-channel currents were recorded from the same BLM preparation when the aqueous solutions surrounding the BLM were repeatedly exchanged, demonstrating the tolerance of the present BLM to repetitive solution exchanges. Such stable membranes enable analysis of channel functions under various solution conditions from the same BLM, which will open up a variety of applications including a high throughput drug screening for ion channels.

Modulating the activity of the channel-forming segment of Vpr protein from HIV-1

Viral protein of regulation (Vpr) encoded by human immunodeficiency virus type 1 (HIV-1) is a short auxiliary protein that is 96 amino acids in length. During the viral life cycle, Vpr is released into the blood serum and is able to enter cellular membranes of noninfected cells. In this study a short peptide, Vpr(55-83), was shown to exhibit ion-channel-like activity when reconstituted into (1) planar lipid bilayers and (2) lipid bilayers held at the tip of a glass pipette. The two set-ups led to differences in the oligomerization state of the peptide, which was reflected in differences in the conductance levels. Experiments under applied hydrostatic pressure affect the dynamics of the protein within the membrane.

The orientation effect of gramicidin A on bicelles and Eu3+-doped bicelles as studied by solid-state NMR and FT-IR spectroscopy

We have explored the effect of gramicidin A (gA) on bicelle (Bic) orientation in the absence and presence of Eu(3+) by (31)P and (2)H NMR at different DMPC/gA ratios. FT-IR spectroscopy was used to assess the lipid chain ordering and verify the transmembrane peptide conformation. Our results show a time-dependent flipping of the bilayer normal alignment at high temperatures and high proportion of gA. The results are explained by both the diamagnetic susceptibility anisotropy of the beta(6.3) helical peptides and viscosity of the lipid mixture. The concentration effect of gramicidin on Bic/Eu(3+) is compared to that on Eu(3+)-doped DMPC liposomes. The Bic/Eu(3+) system is no longer oriented in the presence of gA and adopts a vesicular morphology while the peptide incorporation induces the formation of ellipsoidal DMPC/Eu(3+) assemblies aligned with their normal parallel to the magnetic field. The difference is explained in terms of lipid chain disorder and size of the bilayers.