Functional activity of peptide ion channels in tethered bilayer lipid membranes: Review

Abstract

Ion transport across biomembranes plays a major role in living cells. This fundamental function is normally carried out by molecules with both a hydrophobic and a hydrophilic side (amphiphilic molecules), which aggregate within the membrane forming a hydrophilic pore (the ion channel) permitting the selective translocation of permeant ions. Countless papers report the conformation of these ion channels in lipid vesicles using several techniques, such as circular dichroism and solid‐state NMR spectroscopies. However, the functional activity of ion channels can only be investigated by varying the transmembrane potential. This is also the situation in which ion channels operate in commercialized drugs with intracellular targeting activities, of great interest in pharmaceutical research. A suitable biomimetic membrane must consist of a conducting or semiconducting support, whose “heart” is a lipid bilayer in contact with the aqueous solution of interest on one side. The other side must comprise a hydrophilic region thick enough to completely decouple the lipid bilayer from the support, giving rise to a “tethered bilayer lipid membrane” (tBLM). This review aims to describe the numerous efforts made over time to approach this goal, the most recent achievements, and the perspectives of future development. Special emphasis will be placed on the electrochemical aspects of tBLMs, and a qualitative overview of the main optical and scanning probe techniques employed will be provided.

Methods of Measuring Mitochondrial Potassium Channels: A Critical Assessment

“…The latter case is depicted in Figure 5, with the tether being a polyoxyethylene hydrophilic chain modified on one end with thiol functionality for covalent attachment to metal (gold). The various modes of s-PLB formation are described in more detail in several publications [134,135,152,154] and are brilliantly summarized in the review work [158]. Apart from their stability, the s-PLBs also present another important advantage, which cannot be obtained with the free-standing PLB or patch-clamp technique.…”

“…We think that the use of such model membranes deposited on electrodes can greatly enlarge the information gathered with free-standing planar bilayer membranes. Due to their stability, s-PLBs allow for screening of a large library of ionic species, inhibitors/activators, and other molecules affecting the channel activity in a single set of experiments, using the same s-PLB [158,168]. Successful application of s-PLBs may facilitate studies of mitochondrial potassium channels.…”

Effect of pH on Electrochemical Impedance Response of Tethered Bilayer Lipid Membranes: Implications for Quantitative Biosensing

“…EIS has been the popular technique of choice used to test tBLM formation from different lipid compositions mimicking bacterial membrane [8], yeast cell membrane [9] and mammalian cell membrane [10]. EIS based tBLM studies are also employed to understand the interaction of lipid bilayer with membrane proteins [11][12][13][14].…”

“…EIS has been the popular technique of choic used to test tBLM formation from different lipid compositions mimicking bacterial mem brane [8], yeast cell membrane [9] and mammalian cell membrane [10]. EIS based tBLM studies are also employed to understand the interaction of lipid bilayer with membran proteins [11][12][13][14]. tBLMs have been found to have stable insulating membranes for longer durations The study by Vockenroth [15] shows that tBLMs were observed to have stable electrically insulating membranes for as long as three months.…”