Molecular flow resonance Raman effect from retinal and rhodopsin

Area of Science:

• Biophysical Chemistry
• Spectroscopy
• Molecular Biology

Background:

• Retinal isomers are crucial components of visual pigments like rhodopsin.
• Understanding the specific isomer conformation within rhodopsin is key to visual transduction.
• Previous spectroscopic methods faced challenges with the photolabile nature of retinal.

Purpose of the Study:

• To characterize the resonance Raman spectra of various retinal isomers in solution and within bovine rhodopsin.
• To develop a novel technique for measuring photosensitive molecules using Raman spectroscopy.
• To elucidate the specific isomer conformation and linkage within bovine rhodopsin.

Main Methods:

• Resonance enhanced Raman spectroscopy was employed on retinal isomers (all-trans, 11-cis, 9-cis, 13-cis) in solution and CTAB detergent extracts of bovine rhodopsin.
• A new technique was developed to measure photosensitive samples by imposing molecular velocity transverse to the laser beam, minimizing photodegradation.
• Resonance Raman spectra of crystalline retinal isomers were also measured for comparison.

Main Results:

• Each retinal isomer exhibited a unique and characteristic Raman spectrum.
• The Raman spectrum of 11-cis-retinal closely resembled that of rhodopsin, while 9-cis-retinal's spectrum was similar to isorhodopsin.
• Data confirmed a protonated Schiff base linkage between retinal and opsin, and suggested 11-cis-retinal in solution exists as a mixture of 12-s-trans and 12-s-cis conformers, with rhodopsin adopting a (distorted) 12-s-trans conformation.

Conclusions:

• The developed Raman spectroscopy technique is effective for studying photosensitive molecules like retinal.
• The spectral data provide strong evidence for the specific conformation of 11-cis-retinal within bovine rhodopsin.
• The findings support the role of specific retinal conformations in the function of visual pigments.