Torsion potential works in rhodopsin

Area of Science:

• Biochemistry
• Computational Chemistry
• Molecular Biophysics

Background:

• Rhodopsin's cis-trans photoisomerization is crucial for vision.
• The protein environment and chromophore interactions influence this process.

Purpose of the Study:

• To investigate the role of the protein environment and intramolecular chromophore interactions in rhodopsin's photoisomerization.
• To analyze the specific torsion potential affecting the 11-cis retinal chromophore.

Main Methods:

• Development and application of a novel theoretical method: site-specific force field switch (SFS).
• Modification of rhodopsin's chromophore or binding pocket force fields.
• Comparison of equilibrium conformations and stored energy in modified versus native rhodopsins.

Main Results:

• The SFS method effectively targets torsion potentials, particularly the C11=C12 bond of 11-cis retinal.
• Reducing the C11=C12 twisting force constant to zero resulted in a significant twist (~ -80 degrees) and relaxation energy (~10 kcal/mol).
• Altering other double bond force constants did not induce similar large twists, indicating specificity.

Conclusions:

• A specific torsion potential acts on the C11=C12 bond of the rhodopsin chromophore in its ground state.
• This torsion potential facilitates bond-specific cis-trans photoisomerization, aligning with established torsion models.
• The SFS method provides detailed insights into the origin of this torsion potential based on chromophore structure and protein conformation.