Cell-directed localization and orientation of a functional foreign transmembrane protein within a silica nanostructure.

A simple procedure for introducing functional exogenous membrane-bound proteins to viable cells encapsulated within a lipid templated silica nanostructure is described. In one method, bacteriorhodopsin (bR) was added directly to a Saccharomyces cerevisiae solution along with short zwitterionic diacylphosphatidylcholines (diC(6) PC) and mixed with equal volumes of a sol precursor solution. Alternatively, bR was first incorporated into liposomes (bR-proteoliposomes) and then added to an S. cerevisiae solution with diC(6) PC, and this was followed by mixing with sol precursor solution. Films prepared from bR added directly to diC(6) PC resulted in bR localization near S. cerevisiae cells in a disordered and diffuse fashion, while films prepared from bR-proteoliposomes added to the diC(6) PC/yeast solution resulted in preferential localization of bR near yeast cell surfaces, forming bR-containing multilayer vesicles. Importantly, bR introduced via proteoliposomes was observed to modulate pH gradients developed at the cell surface, demonstrating both retained functionality and preferential orientation. Localization of liposome lipid or bR did not occur around neutrally charged latex beads acting as cell surrogates, demonstrating that living cells actively organize the multilayered lipid during evaporation-induced self-assembly. We expect this simple procedure for introducing functional and oriented membrane-bound proteins to the surface of cells to be general and adaptable to other membrane-bound proteins. This advance may prove useful in fundamental studies of membrane protein function and cell-cell signaling and in imparting non-native characteristics to arbitrary cells.