Development of membrane-based biosensors: measurement of current from photocycling bacteriorhodopsin on patch clamp...

Our initial work toward developing membrane protein-based biosensors has involved use of bacteriorhodopsin (BR) as a model membrane protein. BR was incorporated into liposomes of a polymerizable lecithin, and was shown to pump protons in response to illumination both before and after polymerization of the lipids. In the work described in this paper, BR was first reincorporated in liposomes of asolectin by consonication with purple membrane. The liposomes, which sustained the function of the protein, were used to form a monolayer at the air-water interface. This monolayer was transferred as a bilayer onto patch electrode. When illuminated with a pulse of 514.5-nm light the lipid/protein patch produced a current spike into the pipette corresponding to events no later than the generation of the 412-nm intermediate, probably caused by pumping of protons across the patch membrane. The experiment demonstrates not only the extreme sensitivity of amperometric detection, but also a small tendency for membrane proteins to preferentially orient in this configuration.