Abstract
The lipid matrix of cellular membranes is an elastic liquid crystalline medium. Its deformations regulate the functionality and interactions of membrane proteins,f membrane-bound peptides, lipid and protein-lipid domains. Gramicidin A (gA) is a peptide, which incorporates into membrane leaflets as a monomer and may form a transmembrane dimer. In both configurations, gA deforms the membrane. The transmembrane dimer of gA is a cation-selective ion channel. Its electrical response strongly depends on the elastic properties of the membrane. The gA monomer and dimer deform the membrane differently; therefore, the elastic energy contributes to the activation barriers of the dimerization and dissociation of the conducting state. It is shown experimentally that channel characteristics alter if gA molecules have been located in the vicinity of the conducting dimer. Here, based on the theory of elasticity of lipid membranes, we developed a quantitative theoretical model which allows explaining experimentally observed phenomena under conditions of high surface density of gA or its analogues, i.e., in the regime of strong lateral interactions of gA molecules, mediated by elastic deformations of the membrane. The model would be useful for the analysis and prediction of the gA electrical response in various experimental conditions. This potentially widens the possible applications of gA as a convenient molecular sensor of membrane elasticity.
Highlights
The lipid bilayer is a fundamental part of biological membranes
Dependence of the membrane elastic energy on the distance between two Gramicidin A (gA) dimers and gA dimer and coaxial pair for membranes formed from DOPC (a) and diphytanoylphosphatidylcholine (DPhPC) (b). (c) Dependence of the elastic contribution to the energy barrier of dissociation of gA conducting state on the distance between two conducting dimers; the dependences are obtained as a difference of blue and green curves in the plots (a) and (b) for membranes formed from DOPC and DPhPC, respectively
In the framework of the theory of elasticity of liquid crystals adapted for lipid membranes, we calculated the dependence of membrane elastic energy on the distance between two dimers, dimer and coaxial pair, dimer and monomer, coaxial pair and monomer of gA
Summary
The amphiphilic nature of lipid molecules provides extremely low permeability of biological membranes to various polar and charged substances [1]. This allows lipid bilayers to fulfill their main barrier function. The typical thickness of a lipid bilayer is about 5 nm [2], and, in most cases, membranes can be considered as infinitely thin elastic films Such a reduction in the space dimensions (from three dimensions to two dimensions) available for diffusing entities may have fundamental significance for the effective functioning of membrane-embedded proteins, which represent about 30% of all the proteins of eukaryotic cells [3,4].
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