Membrane phosphate headgroups' modulation of permeation of alkaline cations in gramicidin channels.

The function of membrane proteins is modulated by lipid bilayers. The permeation of ions in gramicidin A channels (gA) is markedly distinct in monoglyceride and phospholipid membranes. It was previously demonstrated that membrane phosphate headgroups accelerate the rate of proton transfer in gA.

Enhancement of proton transfer in ion channels by membrane phosphate headgroups.

The transfer of protons (H+) in gramicidin (gA) channels is markedly distinct in monoglyceride and phospholipid membranes. In this study, the molecular groups that account for those differences were investigated using a new methodology. The rates of H+ transfer were measured in single gA channels reconstituted in membranes made of plain ceramides or sphingomyelins and compared to those in monoglyceride and phospholipid bilayers.

Proton transfer in water wires in proteins: modulation by local constraint and polarity in gramicidin a channels.

The transfer of protons in membrane proteins is an essential phenomenon in biology. However, the basic rules by which H(+) transfer occurs in water wires inside proteins are not well characterized. In particular, the effects of specific atoms and small groups of atoms on the rate of H(+) transfer in water wires are not known.

Proton transfer in gramicidin water wires in phospholipid bilayers: attenuation by phosphoethanolamine.

The transfer of protons in water wires was studied in native gramicidin A (gA), and in the SS- and RR-diastereoisomers of dioxolane-linked gA channels (SS and RR channels). These peptides were incorporated into membranes comprised of distinct combinations of phospholipid headgroups and acyl chains. Quantitative relationships between single channel conductances to H+ (g(H)) and [H+] were determined in distinct phospholipid membranes, and are in remarkable contrast with results previously obtained in monoglyceride membranes.

Et tu, Grotthuss! and other unfinished stories.

This review article is divided into three sections. In Section 1, a short biographical note on Freiherr von Grotthuss is followed by a detailed summary of the main findings and ideas present in his 1806 paper. Attempts to place Grotthuss contribution in the context of the science done at his time were also made.

The transfer of protons in water wires inside proteins.

The translocation of protons across membrane proteins is an essential phenomenon in biology. Only in recent years however, have we started to study in detail some of the basic features of proton transfer in water molecules inside proteins at the single molecule level. Due to their truly unique features, gramicidin-based ion channels have been used to probe proton transfer in both experimental and computational fronts.

Kinetic isotope effects of proton transfer in aqueous and methanol containing solutions, and in gramicidin A channels.

The electrochemical conductivities of HCL and DCI were measured in: H(2)O and D(2)O; in methanol and fully deuterated methanol; and in water-methanol solutions. The single channel conductances to H(+) (g(H)) and D(+) (g(D)) in various gramicidin A (gA) ion channels incorporated in glycerylmonooleate planar bilayers were also measured. Kinetic isotope effects (KIE) were estimated from the ratio of conductivity measurements.

Theoretical study of the structure and dynamic fluctuations of dioxolane-linked gramicidin channels.

Gramicidin is a hydrophobic peptide that assembles as a head-to-head dimer in lipid membranes to form water-filled channels selective to small monovalent cations. Two diastereoisomeric forms, respectively SS and RR, of chemically modified channels in which a dioxolane ring links the formylated N-termini of two gramicidin monomers, were shown to form ion channels. To investigate the structural basis underlying experimentally measured differences in proton conductance in the RR and SS channels, we construct atomic-resolution models of dioxolane-linked gramicidin dimers by analogy with the native dimer.

Proton transfer in gramicidin channels is modulated by the thickness of monoglyceride bilayers.

The thickness of monoglyceride planar bilayers has significant effects on the transfer of protons in both native gramicidin A (gA) and in covalently linked SS- and RR-dioxolane-linked gA proteins. Planar bilayers with various thicknesses were formed from an appropriate combination of monoglyceride with various fatty acid lengths and solvent. Bilayer thicknesses ranged from 25 A (monoolein in squalene) to 54 A (monoeicosenoin in decane).

On the origin of closing flickers in gramicidin channels: a new hypothesis.

The submillisecond closing events (flickers) and the single channel conductances to protons (g(H)) were studied in native gramicidin A (gA) and in the SS and RR diastereoisomers of dioxolane-linked gA channels in planar bilayers. Bilayers were formed from glycerylmonooleate (GMO) in various solvents. In GMO/decane (thick) bilayers, the largest flicker frequency occurred in the SS channel (39 s(-1)), followed by the RR (4 s(-1)) and native gA channels (3 s(-1)).

Thermodynamic view of activation energies of proton transfer in various gramicidin A channels.

The temperature dependencies (range: 5-45 degrees C) of single-channel proton conductances (g(H)) in native gramicidin A (gA) and in two diastereoisomers (SS and RR) of the dioxolane-linked gA channels were measured in glycerylmonooleate/decane (GMO) and diphytanoylphosphatidylcholine/decane (DiPhPC) bilayers. Linear Arrhenius plots (ln (g(H)) versus K(-1)) were obtained for the native gA and RR channels in both types of bilayers, and for the SS channel in GMO bilayers only. The Arrhenius plot for proton transfer in the SS channel in DiPhPC bilayers had a break in linearity around 20 degrees C.