Mimicking Microbial Rhodopsin Isomerization in a Single Crystal

Area of Science:

• Biochemistry
• Structural Biology
• Photochemistry

Background:

• Bacteriorhodopsin is a simple, abundant phototropic system converting light to a proton gradient.
• Understanding its design elements can lead to new photoactive proteins.

Purpose of the Study:

• To create and study a microbial rhodopsin mimic using an orthogonal protein system.
• To illuminate design principles for novel photoactive proteins.

Main Methods:

• Developed a microbial rhodopsin mimic using a small soluble protein template.
• Analyzed photoisomerization of retinal (all-trans to 13-cis) and thermal relaxation in a single crystal.
• Investigated the role of steric interactions between the chromophore and protein.
• Introduced a single mutation to assess changes in protein function.

Main Results:

• The mimic successfully photoisomerizes retinal and thermally relaxes, replicating the bacteriorhodopsin photocycle.
• A tuned steric interaction was identified as crucial for selective retinal isomerization.
• A single mutation transformed the system into a protein photoswitch, uncoupled from chromophore photoisomerization.

Conclusions:

• A soluble protein can be engineered to mimic bacteriorhodopsin's light-driven photocycle.
• Steric interactions are key to controlling chromophore photoisomerization in rhodopsin mimics.
• Protein photoswitches can be generated through targeted mutations, independent of chromophore isomerization.