Direct transmembraneous reconstitution of bacteriorhodopsin into planar phospholipid bilayers

A light-powered bio-capacitor with nanochannel modulation

An artificial bio-capacitor system is established, consisting of the proton-pump protein proteorhodopsin and a modified alumina nanochannel, inspired by the capacitor-like behavior of plasma membranes realized through the cooperation of ion-pump and ion-channel proteins. Capacitor-like features of this simplified system are realized and identified, and the photocurrent duration time can be modulated by nanochannel modification to obtain favorable square-wave currents.

Direct reconstitution of bacteriorhodopsin into planar phospholipid bilayers--detergent effect

This paper describes how the structure and concentration level of a detergent used for substitution after bacteriorhodopsin (bR) solubilization affect the reconstitution of the bR into phospholipid planar bilayers. A direct insertion method was used for the bR reconstitution into the bilayers. Two detergents representing the two major types were used: sodium deoxycholate with a cholane-ring structure, and octylglucoside with a linear (or chain) structure. We then characterized the reconstitution for the two detergents by considering the detergent separation profiles and the photocurrent variations upon addition of lanthanum chloride and the protonophore FCCP (carbonylcyanide-p-trifluoromethoxyphenylhydrazone). We found that for successful transmembrane reconstitution of bR the detergent with the cholane-ring structure was preferable to that with the linear structure when the detergent concentration was above its critical micellar concentration. This preference was explained by the ease with which the detergent with the cholane-ring structure was removed from protein compared to that with the linear structure. Finally, we proposed a scheme for the reconstitution of the protein.

A new system for the measurement of electrogenicity produced by ion pumps using a thin polymer film: examination of wild type bacteriorhodopsin and the D96N mutant over a wide pH range

We developed a new assay system for the measurement of capacitive electric currents generated by ion pumps using the thin polymer film 'Lumirror' (Toray Co., Japan). This system enables us to examine the electrogenicity of ion pumps over a wide range of experimental conditions with high reproducibility due to the mechanical and chemical stability, the high electric resistance and the high electric capacitance of the thin polymer film. Using this method, we examined the photoelectric response of wild type bacteriorhodopsin and its D96N mutant over a wide pH range (2.8-10.0). The results were explained in terms of the affinities of the proton binding sites for translocated protons. A possibility that the direction of the proton transfer from the Schiff base was influenced by the protonation/deprotonation state of the surrounding proton binding sites was suggested. We also found that this film can be used as a substrate for atomic force microscopy (AFM) samples and hence the active purple membrane was observed with AFM.

Introduction to the Bioelectronic Devices Project in Japan

The Bioelectronic Devices Project was organized in Japan as a 10-year national project and it has been working toward developing fundamental key technologies for designing and assembling innovative information-processing devices by realizing the excellent functions specifically found in molecular assemblies and information processing of living organisms. The project is now in the third year of the second phase (the 8th year of its 10-year duration) and researchers have been trying to elucidate the specific characters of the prototype devices. The outline of this challenging project is given with the latest experimental results.