Membrane Protein Activity Induces Specific Molecular Changes in Nanodiscs Monitored by FTIR Difference Spectroscopy

Area of Science:

• Biophysics
• Membrane protein biophysics
• Lipid-protein interactions

Background:

• Integral membrane proteins' function is modulated by neighboring lipids.
• Membrane proteins undergo conformational changes upon activation, affecting the lipid bilayer.
• Understanding these reciprocal interactions is crucial for membrane biology.

Purpose of the Study:

• To investigate the dynamic interplay between membrane proteins and the lipid bilayer.
• To characterize how protein structural changes perturb the lipidic environment.
• To compare protein-induced lipid perturbations with mechanically induced membrane tension.

Main Methods:

• Fourier-transform infrared (FTIR) spectroscopy to monitor lipid vibrational bands.
• Reconstitution of various microbial membrane proteins (rhodopsins, cytochrome c oxidase) into lipid nanodiscs.
• Utilizing isotopologues and 13C-labeling for detailed analysis.
• Employing the light-activatable lipid analogue AzoPC to induce controlled membrane tension.

Main Results:

• The ν(C = O) ester band of the glycerol backbone serves as a reporter for lipid collective state changes.
• Transmembrane protein activation induces mechanical changes that perturb the nanodisc lipids' phase and/or packing.
• The scaffold protein's structure also adapts to mechanical expansion of the lipid bilayer.

Conclusions:

• Lipid vibrational spectroscopy effectively reports on lipid collective state changes induced by membrane proteins.
• Membrane protein conformational dynamics directly influence the surrounding lipid bilayer's physical properties.
• These findings provide insights into the functional coupling between membrane proteins and their lipid environment.