Adaptation of Green Proteorhodopsin to Changes in Membrane Lipid Composition
The protein studied in this thesis is Proteorhodopsin (PR), which is linked to starvation states in marine bacteria. This work examines PR membrane system stability using FTIR. The stable membrane systems, found using FTIR, are further examined using multiple methodologies. The findings show lipid loss over time for PR membrane systems that contained only PC lipids or a DOPC/DOPS mixture. Lipid systems containing DOPE/DOPG were found to be stable and were compared to systems containing DMPC/DMPA in further experiments. These systems mimic the changes involved in the transition from non-starvation to starvation state, suggesting DMPC/DMPA as a suitable native membrane model for structural study of PR. Photocycle and titration experiments provide evidence of a shift in the pKa of D97 (DMPC/DMPA PR 6.6, DOPE/DOPG PR 7.5). CANCO experiments showed minimal changes in observable residues, however further NMR studies are required for full evaluation.