Reconstitution of the pore-forming toxin alpha-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 in to supported bilayer membranes (SBMs). Here, we describe the physical prope rties of SBMs formed by a layer of egg-phosphatidyl choline deposited on a monolayer of either 18-octadecyl-1-thiahexa(ethylene oxide) [THEO-C-18] or n-octadecanethiol on gold. We also show that the pore-forming protein a-hem olysin (alpha HL) self-assembles in these thin films. The insulating proper ties and the stability of the THEO-C-18 self-assembled monolayers were char acterized by ac impedance spectroscopy and voltammetry. An impedance model, including constant phase elements, was determined for THEO-C-18 monolayers and the SBMs. Cyclic voltammetry measurements demonstrated virtually full blockage of ferricyanide oxidation and reduction by the THEO-C-18 monolayer s. The monolayer stability test showed that, at applied potentials between +/-400 mV versus Ag/AgCl in 3 M KCl, the electrical properties of THEO-C-18 SAMs did not change with time. The reconstitution bf alpha HL in SBMs caus ed a decrease in impedance and an increased permeability to redox ions. The impedance model parameters suggest that alpha HL partially penetrates into the SBMs, increasing the dielectric constant of the alkane portion of the monolayers. The complete reconstitution of alpha HL that could provide the free access of the redox ions to the metal surface was not observed in thes e thin films.