α-Tocopherol Is Well Designed to Protect Polyunsaturated Phospholipids: MD Simulations

Area of Science:

• Biochemistry
• Molecular Biophysics
• Membrane Biology

Background:

• Alpha-tocopherol (αtoc) is the primary lipid-soluble antioxidant in membranes.
• Its role in protecting polyunsaturated lipids from oxidation is crucial but its molecular mechanisms are debated.
• Understanding αtoc's interaction with different lipid structures is key to its protective function.

Purpose of the Study:

• To investigate the role of molecular structure in alpha-tocopherol's membrane protection function.
• To elucidate the atomistic mechanisms of αtoc interaction with polyunsaturated and monounsaturated lipid bilayers.
• To simulate αtoc behavior in membranes using molecular dynamics.

Main Methods:

• Atomistic molecular-dynamics simulations in the NPT ensemble.
• Simulations of hydrated lipid bilayers: SDPC (polyunsaturated) and SOPC (monounsaturated) with 20 mol % αtoc at 37°C.
• Validation using solid-state 2H nuclear magnetic resonance and neutron diffraction experiments.

Main Results:

• High lipid chain disorder, particularly with docosahexaenoic acid (DHA), increases αtoc's interaction with the bilayer surface.
• αtoc's chromanol group penetrates deeper into disordered polyunsaturated membranes.
• αtoc flip-flops across SDPC bilayers significantly faster (submicrosecond) than across SOPC bilayers.

Conclusions:

• Molecular structure dictates αtoc's membrane dynamics and protective efficacy.
• Disordered polyunsaturated chains facilitate αtoc's radical trapping and regeneration mechanisms.
• These findings reveal how αtoc effectively protects polyunsaturated membranes against lipid peroxidation.