A Photoisomerizing Rhodopsin Mimic Observed at Atomic Resolution

Area of Science:

• Biochemistry
• Structural Biology
• Photochemistry

Background:

• Rhodopsin proteins mediate essential light-dependent biological processes.
• The core mechanism involves photoisomerization of the protein-bound retinylidene protonated Schiff base (PSB).
• Replicating this in engineered systems has been challenging.

Purpose of the Study:

• To develop novel rhodopsin mimics for studying protein/chromophore interactions.
• To create an engineered system capable of thermal and photochemical retinylidene PSB isomerization.
• To characterize the isomerization process at atomic resolution.

Main Methods:

• Utilized intracellular lipid binding proteins as scaffolds for rhodopsin mimic construction.
• Employed thermal and photochemical methods to induce isomerization of the retinylidene PSB.
• Analyzed isomerization at atomic resolution via X-ray crystallography, enabling quantitative interconversion of isomers in crystalline state.

Main Results:

• Successfully developed a rhodopsin mimic system.
• Demonstrated specific thermal and photochemical isomerization of the retinylidene protonated Schiff base.
• Observed significant pKa changes of the imine upon isomerization, comparable to those in natural opsins like bacteriorhodopsin and visual opsins.
• Characterized the isomerization event at atomic resolution in the crystalline state.

Conclusions:

• Engineered rhodopsin mimics provide a platform for fundamental studies of protein/chromophore interactions.
• The developed system successfully mimics the light-driven isomerization and associated pKa shifts seen in natural visual pigments.
• This work offers insights into the molecular mechanisms underlying light sensing in biological systems.