Resolving voltage-dependent structural changes of a membrane photoreceptor by surface-enhanced IR difference...

Area of Science:

• Biophysics
• Spectroscopy
• Membrane protein dynamics

Background:

• Membrane proteins, crucial for cellular functions, are challenging to study structurally.
• Electrophysiology lacks structural sensitivity for membrane protein analysis.

Purpose of the Study:

• To present spectroelectrochemical data on vibrational changes in membrane proteins.
• To demonstrate the capability of SEIDAS for resolving structural changes and ion transfer.

Main Methods:

• Surface-enhanced IR difference absorption spectroscopy (SEIDAS) applied to a single membrane protein monolayer.
• Utilizing vibrational changes perpendicular to the surface to determine angular bond orientations.
• Applying negative membrane potentials to observe effects on protein function.

Main Results:

• SEIDAS resolved structural changes in sensory rhodopsin II, including the protein backbone and retinal cofactor.
• Single ion transfer events were detected and correlated with structural changes.
• A negative membrane potential (-0.3 V) selectively halted light-induced proton transfer at D75.
• Transmembrane electric fields were found to affect specific proton transfer reactions by raising energy barriers.

Conclusions:

• SEIDAS provides unprecedented spatial sensitivity and temporal resolution for studying membrane protein mechanisms.
• The technique is effective for investigating voltage-dependent processes in ion channels and transporters.
• SEIDAS offers a new approach to elucidate the mechanisms of ion transfer across membranes.