Bacteriorhodopsin (bR) as an electronic conduction medium: current transport through bR-containing monolayers

Area of Science:

• Biomolecular electronics
• Protein biophysics
• Membrane protein function

Background:

• Electron transport (ET) studies in proteins face challenges in reproducible experimental setups.
• Bacteriorhodopsin (bR), a robust transmembrane proton pump, is a model for biomolecular electronics.
• Previous studies on dry bR focused on photovoltage and photoconduction, not direct ET.

Purpose of the Study:

• To investigate electron transport (ET) through bacteriorhodopsin (bR) in artificial lipid bilayers.
• To determine the role of retinal and light in mediating ET through bR.
• To quantify the rate of ET through bR and compare it to theoretical models.

Main Methods:

• Fabrication of solid "electrode-bilayer-electrode" structures containing bR in artificial lipid bilayers.
• Measurement of electronic current passing through the bR-containing bilayers.
• Investigation of the effect of retinal presence and isomerization on photocurrent.

Main Results:

• Significant electronic current was observed passing through bR-containing bilayers.
• The measured current was over four orders of magnitude higher than predicted for direct peptide tunneling.
• Electron transport was dependent on the presence of retinal and its ability to isomerize upon light absorption.
• The contribution of light-driven proton pumping to photocurrent was found to be negligible.

Conclusions:

• Bacteriorhodopsin facilitates electron transport (ET) across lipid bilayers, mediated by its retinal cofactor.
• Light-induced retinal isomerization drives a photo-electron transport effect in bR.
• These findings open new avenues for understanding ET in biological systems and for designing bioelectronic devices.