Reconstitution of the Pore-Forming Toxin α-Hemolysin in Phospholipid/18-Octadecyl-1-thiahexa(ethylene oxide) and Phospholipid/n-Octadecanethiol Supported Bilayer Membranes

We are studying the functional reconstitution of membrane-bound proteins into supported bilayer membranes (SBMs). Here, we describe the physical properties of SBMs formed by a layer of egg-phosphatidyl choline deposited on a monolayer of either 18-octadecyl-1-thiahexa(ethylene oxide) [THEO-C18] or n-octadecanethiol on gold. We also show that the pore-forming protein α-hemolysin (αHL) self-assembles in these thin films. The insulating properties and the stability of the THEO-C18 self-assembled monolayers were characterized by ac impedance spectroscopy and voltammetry. An impedance model, including constant phase elements, was determined for THEO-C18 monolayers and the SBMs. Cyclic voltammetry measurements demonstrated virtually full blockage of ferricyanide oxidation and reduction by the THEO-C18 monolayers. The monolayer stability test showed that, at applied potentials between ±400 mV versus Ag/AgCl in 3 M KCl, the electrical properties of THEO-C18 SAMs did not change with time. The reconstitution of αHL in SBMs caused a decrease in impedance and an increased permeability to redox ions. The impedance model parameters suggest that αHL partially penetrates into the SBMs, increasing the dielectric constant of the alkane portion of the monolayers. The complete reconstitution of αHL that could provide the free access of the redox ions to the metal surface was not observed in these thin films.