Evidence for a 13,14-cis cycle in bacteriorhodopsin

Area of Science:

• Biophysics
• Spectroscopy
• Computational Chemistry

Background:

• Bacteriorhodopsin's photo-cycle is crucial for understanding proton pumping.
• Previous studies utilized resonance Raman and infrared absorption to observe spectral changes during the photo-cycle.
• Discrepancies in spectral assignments necessitate further investigation.

Purpose of the Study:

• To evaluate the consistency of observed vibrational spectra with a proposed bacteriorhodopsin photo-cycle.
• To investigate the influence of different charge environments on vibrational spectra using computational methods.

Main Methods:

• Utilized quantumchemical Modified Neglect of Diatomic Overlap (MNDO) calculations.
• Calculated vibrational spectra for protonated retinal Schiff base isomers.
• Analyzed the impact of charge environments on C-C single bond stretching vibrations.

Main Results:

• The study assessed the agreement between experimental data (Smith et al., Gerwert and Siebert) and theoretical predictions.
• MNDO calculations provided insights into the vibrational characteristics of key photo-cycle intermediates.
• The effect of charge environments on specific vibrational frequencies was elucidated.

Conclusions:

• The findings contribute to validating the proposed bacteriorhodopsin photo-cycle sequence (BR, I->K->L->M->N->O).
• Computational vibrational spectra aid in assigning experimental observations.
• Understanding charge environment effects refines spectral interpretation in biological systems.