Specificity of binding of all-trans-retinyl ester to RPE65

Area of Science:

• Biochemistry
• Molecular Biology
• Vision Science

Background:

• Membrane-bound RPE65 (mRPE65) is a key protein in the visual cycle, binding all-trans-retinyl esters.
• RPE65 is essential for rhodopsin regeneration, a process vital for vision.
• Understanding RPE65 binding specificity is crucial for developing antagonists to study its physiological role.

Purpose of the Study:

• To investigate the binding specificity of mRPE65 towards retinoids and isoprenoids.
• To define the structural determinants of ligand binding in mRPE65.
• To lay the groundwork for designing specific mRPE65 antagonists.

Main Methods:

• Characterization of mRPE65 binding affinities using various retinoid and isoprenoid analogues.
• Systematic modification of the retinoid, linker, and acyl moieties of all-trans-retinyl esters.
• Analysis of binding specificity through dissociation constants.

Main Results:

• mRPE65 binding affinity increases with the hydrophobicity of the fatty acyl group in all-trans-retinyl esters.
• Replacements in the linker region (amide, ketone, ether) showed minimal impact on binding affinity.
• Modifications in the all-trans-retinoid moiety were tolerated, with analogues like E,E-farnesyl palmitate exhibiting similar binding affinity.

Conclusions:

• mRPE65 exhibits moderate specificity for long-chain all-trans-retinyl esters.
• The protein's binding site accommodates variations in the acyl and retinoid moieties.
• These findings provide insights into the structural basis of mRPE65-ligand interactions and guide antagonist design.