Electric Field Driven Changes of a Gramicidin Containing Lipid Bilayer Supported on a Au(111) Surface

Abstract

Langmuir-Blodgett and Langmuir-Schaeffer methods were employed to deposit a mixed bilayer consisting of 90% of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and 10% of gramicidin (GD), a short 15 residue ion channel forming peptide, onto a Au(111) electrode surface. This architecture allowed us to investigate the effect of the electrostatic potential applied to the electrode on the orientation and conformation of DMPC molecules in the bilayer containing the ion channel. The charge density data were determined from chronocoulometry experiments. The electric field and the potential across the membrane were determined through the use of charge density curves. The magnitudes of potentials across the gold-supported biomimetic membrane were comparable to the transmembrane potential acting on a natural membrane. The information regarding the orientation and conformation of DMPC and GD molecules in the bilayer was obtained from photon polarization modulation infrared reflection absorption spectroscopy (PMIRRAS) measurements. The results show that the bilayer is adsorbed, in direct contact with the metal surface, when the potential across the interface is more positive than -0.4 V and is lifted from the gold surface when the potential across the interface is more negative than -0.4 V. This change in the state of the bilayer has a significant impact on the orientation and conformation of the phospholipid and gramicidin molecules. The potential induced changes in the membrane containing peptide were compared to the changes in the structure of the pure DMPC bilayer determined in earlier studies.

Application of Polarization Modulation Infrared Reflection Absorption Spectrosocpy Under Electrochemical Control for Structural Studies of Biomimetic Assemblies

“…Less is known about the impact of the interaction of a protein with a cell membrane on its structure under physiological electric fields [39][40][41]89]. The first results available in literature in this field are reviewed in Section 4.2.…”

“…Moreover, both macroscopic and microscopic properties of a biological membrane such as permeability to ions, capacitance, lateral composition, concentration, orientation and physical state of lipid molecules and the activity and structure of associated proteins can be affected by drugs, changes in electrolyte composition and concentration or the static electric field [144,145]. A combination of IRS, sensitive to the structure of lipid and proteins molecules, to electrochemistry testing macroscopic properties of model membranes such as redox activity, membrane capacity or permeability to ions, giving a possibility to monitor simultaneously potential-dependent changes in lipid bilayers arising from the lipid-protein interaction [39][40][41][42]146] or redox activity of a protein embedded in the membrane [147][148][149][150]. Despite the fact that spectroelectrochemistry provides essential information concerning the structure of molecules at the sub-molecular level, the structure of the entire system exposed to physiological electric fields, these studies are rather rare.…”

“…Predominantly, they concern surface enhanced infrared absorption spectroscopic studies under electrochemical control of transmembrane proteins, involved in redox-reactions, embedded into models of lipid membranes [24,[147][148][149][150]. Below results reporting the application of PM IRRAS under electrochemical control for studies of structural changes in lipid bilayers experiencing specific interactions with proteins are summarized [39][40][41][42].…”

“…In the fourth section the application of in situ IRRAS for structural studies of potential-driven changes in lipid bilayers [9,[30][31][32][33][34][35][36] and protein films [37,38] is reviewed. Recent studies of the impact of lipid-protein interactions on the structure and stability of the membrane exposed to physiological electric fields are summarized and described [39][40][41][42].…”

Vibrational spectroscopy for probing molecular-level interactions in organic films mimicking biointerfaces

“…Lipkowski and co-workers [137] also studied ion channels in supported bilayers mimicking cell-membrane using PM-IRRAS. A mixed bilayer containing 90% of DMPC and 10% of gramicidin (a well-known ion channel) was deposited onto a gold substrate.…”