Valinomycin acts as a channel in ultrathin lipid membranes

Secretory granule protein chromogranin B (CHGB) forms an anion channel in membranes

The CHGB subfamily of secretory granule proteins forms a new family of anion-selective channels by interacting with membranes via two amphipathic α-helices. The channel exhibits higher anion selectivity, larger conductance, higher DIDS-binding affinity, and higher Cl⁻ sensitivity than other known anion channels.

Regulated secretion is an intracellular pathway that is highly conserved from protists to humans. Granin family proteins were proposed to participate in the biogenesis, maturation and release of secretory granules in this pathway. However, the exact molecular mechanisms underlying the intracellular functions of the granin family proteins remain unclear. Here, we show that chromogranin B (CHGB), a secretory granule protein, inserts itself into membrane and forms a chloride-conducting channel. CHGB interacts strongly with phospholipid membranes through two amphipathic α helices. At a high local concentration, CHGB insertion in membrane causes significant bilayer remodeling, producing protein-coated nanoparticles and nanotubules. Fast kinetics and high cooperativity for anion efflux from CHGB vesicles suggest that CHGB tetramerizes to form a functional channel with a single-channel conductance of ∼125 pS (150/150 mM Cl⁻). The CHGB channel is sensitive to an anion channel blocker and exhibits higher anion selectivity than the other six known families of Cl⁻ channels. Our data suggest that the CHGB subfamily of granin proteins forms a new family of organelle chloride channels.

Interfacial tension of bilayer lipid membranes

Interfacial tension is an important characteristic of a biological membrane because it determines its rigidity, thus affecting its stability. It is affected by factors such as medium pH and by the presence of certain substances, for example cholesterol, other lipids, fatty acids, amines, amino acids, or proteins, incorporated in the lipid bilayer. Here, the effects of various parameters to on interfacial tension values of bilayer lipid membranes are discussed.

The mathematically derived and experimentally confirmed results presented in this paper are of importance to the interpretation of phenomena occurring in lipid bilayers. These results can lead to a better understanding of the physical properties of biological membranes. The simple interfacial tension method proposed herein may be successfully used to determine the interfacial tension values of 1:1 lipid-lipid, lipid-cholesterol, lipid-fatty acid, lipid-amine, and lipid-amino acid systems.

Archaeal tetraether bipolar lipids: Structures, functions and applications

Archaea have developed specific tools permitting life under harsh conditions and archaeal lipids are one of these tools. This microreview describes the particular features of tetraether-type archaeal lipids and their potential applications in biotechnology. Natural and synthetic tetraether lipid structures as well as their applications in drug/gene delivery, vaccines and proteoliposomes or as lipid films are reviewed.

Ion channels and pores, made from scratch

We elaborate on the structural diversity well beyond the biological limitations that becomes accessible with synthetic ion channels and pores, and on the importance of advanced nanoarchitecture to create significant function.

The effect of the presence of valinomycin on the interfacial tension of lecithin membrane

The effect of the presence of valinomycin in lecithin membrane on its interfacial tension has been studied. The experiments have been carried out at various forming solution compositions and at various potassium ion concentrations in electrolyte solution. Potassium chloride was used as the electrolyte. A complex was formed between the valinomycin molecule and K+ ion. The following parameters describing the complex were determined: K, the stability constant of the valinomycin-K+ complex and B, partition coefficient. These values are equal to 3.52 x 10(5) m3 mol(-1) and 6.0, respectively.

Highly robust lipid membranes on crystalline S-layer supports investigated by electrochemical impedance spectroscopy

In the present work, S-layer supported lipid membranes formed by a modified Langmuir-Blodgett technique were investigated by electrochemical impedance spectroscopy (EIS). Basically two intermediate hydrophilic supports for phospholipid- (DPhyPC) and bipolar tetraetherlipid- (MPL from Thermoplasma acidophilum) membranes have been applied: first, the S-layer protein SbpA isolated from Bacillus sphaericus CCM 2177 recrystallized onto a gold electrode; and second, as a reference support, an S-layer ultrafiltration membrane (SUM), which consists of a microfiltration membrane (MFM) with deposited S-layer carrying cell wall fragments. The electrochemical properties and the stability of DPhyPC and MPL membranes were found to depend on the used support. The specific capacitances were 0.53 and 0.69 microF/cm(2) for DPhyPC bilayers and 0.75 and 0.77 microF/cm(2) for MPL monolayers resting on SbpA and SUM, respectively. Membrane resistances of up to 80 mega Ohm cm(2) were observed for DPhyPC bilayers on SbpA. In addition, membranes supported by SbpA exhibited a remarkable long-term robustness of up to 2 days. The membrane functionality could be demonstrated by reconstitution of membrane-active peptides such as valinomycin and alamethicin. The present results recommend S-layer-supported lipid membranes as promising structures for membrane protein-based biosensor technology.

Preparation and electrochemical behavior of gramicidin-bipolar lipid monolayer membranes supported on gold electrodes

Gramicidin-containing synthetic bolalipid membranes comprised of 2,2'-di-O-decyl-3,3'-O-1,20-eicosanyl-bis-rac-glycero-1,1'-diphosphocholine (C20BAS) have been synthesized and supported on gold electrodes. Supported membranes were prepared by first depositing a partial bolalipid layer on the electrode using a thioctic acid-modified bolalipid (1'-O-omega-thioctamidetetraethylene glycol-2,2'-di-O-decyl-3,3'-di-O-1,20-eicosanyl-bis-rac-glycero-1-phosphate, SSC20BAS) as an anchoring group, followed by a vesicle fusion step using either pure C20BAS or gramicidin-containing C20BAS (C20BAS-GA) vesicles. The latter configuration was designed to immobilize single, continuously-on channels of gramicidin in the C20BAS membrane. Vesicle deposition to form supported bolalipid monolayer membranes was monitored by impedance spectroscopy and cyclic voltammetry. Impedances were observed to increase with vesicle deposition time. Pretreatment of the impedance electrode with SSC20BAS accelerated the supported monolayer membrane deposition rate. Impedances decreased in a gramicidin concentration-dependent manner when gramicidin was incorporated into the C20BAS membrane. These supported bolalipid membranes are also surprisingly inert to organic solvent exposure (CH(3)CH(2)OH;CH(2)Cl(2)), suggesting that they may serve as robust host matrices for integral membrane protein-based sensors.

Spectroscopic studies of PhTX facilitated cation movement across membranes

Philanthotoxins, noncompetitive inhibitors of the nicotinic acetylcholine receptor and various glutamate receptors, were found to be capable of mediating cation transport across lipid bilayers. With respect to the relatively weak binding constants of these amphiphilic polyamines to neuronal receptor proteins, this finding implies that their interaction with cell membranes might have to be considered in addition to that with protein receptors to fully understand the molecular mechanism of these neurotoxins.