Artificial Phytanyl-Chained Glycolipid Vesicle Membranes with Low Proton Permeability are Suitable for Proton Pump Reconstitution Matrices

Abstract

This chapter presents a light-driven proton pump, bacteriorhodopsin (BR), reconstituted into an artificial phytanyl-chained glycolipid, 1,3-di-o-phytanyl-2-o-(β-D-maltotriosyl) glycerol (Mal3(Phyt)2) vesicle membranes, the proton permeability of which is much lower than that of straight-chained phospholipid, egg yolk phosphatidylcholine (EPC) membranes. Although BR had an inside-out orientation and translocated protons from the vesicle outside to the inside during illumination in both cases of Mal3(Phyt)2 and EPC membranes, BR reconstituted into Mal3(Phyt)2 membranes exhibited a prolonged transmembrane pH gradient because of the lower proton leak rates. Mal3 (Phyt)2 vesicles exhibit ca. 10-fold longer half-life than EPC vesicles, thereby suggesting that the proton efflux from the internal aqueous phase of Mal3 (Phyt)2 vesicles is much slower than that from EPC vesicles. The result suggests that artificial phytanyl-chained glycolipid membranes with low proton permeability are advantageous for stable and functional reconstitution of energy-conversion membrane proteins, thereby allowing an efficient generation and/or consumption of a transmembrane proton motive force.