Effect of Gramicidin D on the Compressibility and Volume Fluctuations of DPPC – Peptide Bilayers: A Densitometry and Sound Velocimetry Study

Abstract

The effects of increasing gramicidin D (gD) concentration on the partial specific volume, v o , and the adiabatic compressibility coefficient of the lipid, β S lipid of the bilayer reveals a continual decrease in  o and β S lipid (within the range of concentration studied) with concentration, except between 5 and 7.5 %, where a very slight decrease was observed. At gD concentrations higher than 5 mol%, the isothermal compressibility coefficient, β T lipid is greater than β S lipid at the gel-fluid region by  10 -20 % in the entire temperature range covered. The maximum value of the relative volume fluctuation of 12 % is reached for DPPC at the main transition, and is strongly dampened upon addition of gD. A gradual decrease in the calculated relative volume fluctuations with gD concentration at T m is observed between concentrations 1 and 10 mol%.

Can gramicidin ion channel affect the dipole potential of neighboring phospholipid headgroups?

“…Gramicidin has a low solubility in water (≤ 1 × 10 −4 μM according to Hladky and Haydon [32]) and has been found to partition strongly into the hydrophobic region of lipid membranes [33]. Hence, at the 0.1 μM gramicidin concentration adopted herein, much higher than its solubility value in pure water, it is quite reasonable for its concentration in the lipid bilayer to assume a value close to the 1:10 peptide/lipid molar ratio adopted in a theoretical analysis of hydrophobic matching [34], in a densitometry and sound velocimetry study on the effect of gramicidin [35], and in a STM imaging of gramicidin in a dimyristoylphosphatidylcholine (DMPC) monolayer on Au [36]. In particular, the counting of the lipid molecules surrounding each gramicidin channel yields an average number of 7 ± 1 [36], which is consistent with molecular dynamics calculations that assume eight nearestneighbor lipids [37].…”

The Effect of Proteome and Lipidome on the Behavior of Membrane Bound Systems in Thermally-Assisted Acoustophoresis

“…This antimicrobial peptide is in fact a mixture of pore forming peptides (gramicidin A 80%, B 6% and C 14%), 156 called collectively gramicidin D. 35 Gramicidin D has a linear chain made of 15 amino acids, 157 as opposed to gramicidin S that forms a cyclic peptide chain. 158 Alamethicin is another channelforming peptide antibiotic, that can induce voltage-dependent ion channels in lipid membranes. 159 Despite being made of only 20 amino acids, alamethicin exhibits channeling activity that is suggested to be relevant to that of physiological channel proteins which typically consist of 2,000 or more amino acids.…”

“…35 These pore forming peptides have also been acting as model systems in various studies 17,[153][154][155] aiming at evaluating the changes of membrane electrical properties upon insertion of peptides 35 . These peptides are produced by soil bacterial species Bacillus brevis and are active against Gram-positive bacteria except for the Gram-positive bacilli against selected Gram-negative organisms, such as Neisseria bacteria 158 . Gramicidin D has a linear chain made of 15 amino acids 157 , opposed to gramicidin S that forms a cyclic peptide chain 158 .…”

“…These peptides are produced by soil bacterial species Bacillus brevis and are active against Gram-positive bacteria except for the Gram-positive bacilli against selected Gram-negative organisms, such as Neisseria bacteria 158 . Gramicidin D has a linear chain made of 15 amino acids 157 , opposed to gramicidin S that forms a cyclic peptide chain 158 . Gramicidin D create active pores/channels in lipid membrane to enhance the transport of small cations by inserting into the hydrophobic region of membranes [188][189][190][191][192] .…”

“…Gramicidin D create active pores/channels in lipid membrane to enhance the transport of small cations by inserting into the hydrophobic region of membranes [188][189][190][191][192] . Figure 3.2 shows schematic of building blocks of a bilayer membrane containing PC lipid molecules such as DPPC and transmembrane peptides such as gramicidin D. It was shown that the chain melting transition of lipids can be changed upon insertion of peptides and proteins 158,193 . This changes in transition profile can be observed either as broadening and/or shifting the curve to lower or higher temperatures.…”