Bacteriorhodopsin (BR), a visible-light absorbing membrane protein, was encapsulated in sol-gel derived porous silica and titanium dioxide (titania) monoliths in its native purple membrane form. Sol-gel synthesis procedure was optimized to minimize the amount of alcohol in the pores to avoid denaturation of the entrapped protein. Fluorescence spectroscopy was used to investigate the effect of pH on thermal denaturation of bacteriorhodopsin in silica. The amount of buffer added during the gelation of silica effected the stability of the protein at elevated temperatures. Intrinsic tryptophan fluorescence emission and anisotropy measurements showed that the protein was more stable at higher temperatures when pH was close to neutral. Solvent accessibility determined using acrylamide quenching of tryptophan residues indicated similar environment for the protein before and after entrapment. The absorbance spectrum of BR entrapped in both silica and titania gels demonstrated retention of the protein tertiary structure. It was also shown that the protein could undergo conformational changes from its dark to light adapted states after entrapment in both matrices. Förster resonance energy transfer between tryptophan residues and titania sol nanoparticles suggested there is less than 10 nm separation between bacteriorhodopsin and titania surface. These results lay the groundwork for development of functional biocompatible porous materials using membrane protein encapsulation.

Investigating interactions and stability of bacteriorhodopsin upon entrapment in sol-gel derived porous materials

2019 Spring National Meeting

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