(98c) Incorporation of Photo-Responsive Membrane Protein Species into Nanostructured Silica for Light-Driven Ion Transport

Membrane proteins are versatile biomolecules with diverse functionalities that impart sensing, signaling, transport, or catalytic properties that support the viabilities of biological cells. Such functionalities are highly selective to particular ions or molecules and often occur at high rates, which would be attractive for technological applications, such as chemical or biological sensing, separations, bioanalytics, and energy conversion. To effectively exploit membrane proteins for technological purposes often requires their incorporation into synthetic host materials that enable the proteins to function stably and be integrated into macroscopic devices. One interesting example is the membrane protein proteorhodopsin, which functions as a light-driven H⁺-ion-pump that might be harnessed for photochemical energy conversion. Synthetic host membranes that contain macroscopically aligned proteorhodopsin species are expected to generate bulk ion gradients across host materials under illumination. Here, we present a solution-based synthetic protocol that allows high concentrations (up to 15 wt%) of active orientationally ordered proteorhodopsin species to be incorporated within nanostructured silica membrane hosts. Synthesis conditions and compositions were selected to stabilize proteorhodopsin molecules in the presence of the structure-directing surfactant and soluble network-forming silica species that co-assemble to form nanostructured silica host matrices, as established by small-angle X-ray diffraction analyses. Multidimensional solid-state NMR spectra show that proteorhodopsin molecules incorporated within nanostructured silica hosts retain native-like structures, though with some interesting differences. The optical absorbance behaviors of proteorhodopsin within the synthetic hosts are analogous to the photochemical reaction cycle of proteorhodopsin in native-like environments associated with the active transport of H⁺-ions. The synthesis protocol is expected to be general and has been adapted to incorporate other functionally active membrane proteins within nanostructured silica host membranes. The versatile nanostructured silica-surfactant host materials open opportunities to integrate membrane proteins and their diverse functionalities into synthetic semi-permeable membranes.