Photoisomerization detected in a fully wavelength-tunable rhodopsin mimic system

Area of Science:

• Biochemistry
• Structural Biology
• Photochemistry

Background:

• Human retinol-binding protein II (hCRBPII) binds and transports retinol.
• The retinylidene protonated Schiff base is a key chromophore in visual pigments.
• Understanding its photoisomerization is crucial for visual cycle and protein function studies.

Purpose of the Study:

• To investigate the photoisomerization mechanism of the retinylidene protonated Schiff base within hCRBPII.
• To elucidate the role of water molecules and protein environment in this photoisomerization process.
• To explore novel photoswitching mechanisms beyond chromophore isomerization.

Main Methods:

• UV-visible spectroscopy for characterizing spectral changes.
• Atomic-resolution X-ray crystallography for structural analysis.
• Investigating light-induced alterations in the protein's binding pocket.

Main Results:

• Characterized the 15-cis/all-trans photoisomerization of the retinylidene protonated Schiff base in hCRBPII.
• Observed light-induced dehydration of the protein's binding pocket.
• Demonstrated significant alteration of the protonated Schiff base's pK_a due to light-induced environmental changes.

Conclusions:

• Photoswitching in hCRBPII can be mediated by light-induced protein environment reorganization, specifically dehydration.
• This mechanism offers novel pathways for photoswitching independent of chromophore isomerization.
• Highlights the dynamic interplay between protein structure, water molecules, and chromophore function.