Vitamin E Has Reduced Affinity for a Polyunsaturated Phospholipid: An Umbrella Sampling Molecular Dynamics...

Area of Science:

• Biochemistry
• Molecular Biophysics
• Cell Biology

Background:

• Vitamin E is a crucial lipid-soluble antioxidant essential for protecting cell membranes from oxidation.
• The preferential interaction of vitamin E with polyunsaturated phospholipids, the most oxidation-vulnerable lipids, remains unclear.

Purpose of the Study:

• To investigate the binding affinity of alpha-tocopherol (αtoc) to polyunsaturated vs. monounsaturated phospholipids in lipid bilayers.
• To determine if vitamin E preferentially associates with polyunsaturated phospholipids for enhanced membrane protection.

Main Methods:

• Utilized umbrella sampling molecular dynamics simulations to compare αtoc binding.
• Analyzed potential of mean force calculations to determine binding energies within bilayers.
• Simulated bilayers composed of polyunsaturated 1-stearoyl-2-docosahexaenoylphosphatidylcholine (SDPC) and monounsaturated 1-stearoyl-2-oleoylphosphatidylcholine (SOPC).

Main Results:

• Alpha-tocopherol binding energy was lower in SDPC bilayers (16.7 ± 0.3 kcal/mol) compared to SOPC bilayers (18.3 ± 0.4 kcal/mol).
• The reduced binding in SDPC is attributed to the increased disorder of polyunsaturated fatty acids, leading to looser packing.
• Bilayer deformation during αtoc desorption suggests contributions from phosphatidylcholine (PC)–PC and αtoc–PC interactions.

Conclusions:

• The study's findings do not support the hypothesis that vitamin E preferentially interacts with polyunsaturated phospholipids.
• Vitamin E exhibits weaker binding to more disordered, polyunsaturated phospholipid bilayers.