Photo-induced proton gradients and ATP biosynthesis produced by vesicles encapsulated in a silica matrix

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Abstract
Sol–gel immobilization of soluble proteins has proven to be a viable method for stabilizing a wide variety of proteins in transparent inorganic matrices1,2,3. The encapsulation of membrane-bound proteins has received much less attention, although work in this area suggests potential opportunities in microarray technology and high-throughput drug screening4,5. The present paper describes a liposome/sol–gel architecture in which the liposome provides membrane structure and protein orientation to two transmembrane proteins, bacteriorhodopsin (bR) and F0F1-ATP synthase; the sol–gel encapsulation converts the liposomal solution into a robust material without compromising the intrinsic activity of the incorporated proteins. Here we report on two different proteoliposome-doped gels (proteogels) whose properties are determined by the transmembrane proteins. Proteogels containing bR proteoliposomes exhibit a stable proton gradient when irradiated with visible light, whereas proteogels containing proteoliposomes with both bR and F0F1-ATP synthase couple the photo-induced proton gradient to the production of ATP. These results demonstrate that materials based on the liposome/sol–gel architecture are able to harness the properties of transmembrane proteins and enable a variety of applications, from power generation and energy storage to the powering of molecular motors, and represent a new technology for performing complex chemical synthesis in a solid-state matrix.