Lipid Membrane Leaflets Unzip upon Hybridization with Polymer-Rich Nanodomains

Area of Science:

• Materials Science
• Biophysics
• Polymer Science

Background:

• Artificial biomimetic membranes are of interest for selective permeability.
• Hybrid membranes formed by phospholipids and block copolymers mimic biomembrane properties.
• Lateral phase separation in hybrid membranes regulates their function.

Purpose of the Study:

• To understand the molecular and physical cues governing domain formation in hybrid phospholipid-block copolymer membranes.
• To elucidate the morphology of hybrid membranes at varying polymer content.
• To investigate the self-assembly behavior of phosphatidylcholine-cholesterol bilayers with poly(butadiene-b-ethylene oxide).

Main Methods:

• Coarse-grained molecular dynamics simulations.
• High-resolution cryogenic electron microscopy.

Main Results:

• Hybrid bilayers exhibit two distinct phase-separated morphologies.
• At polymer fractions >10 mol%, lipid-rich and polymer-rich domains form as expected.
• At low polymer content, a novel morphology emerges where bilayer leaflets unzip to incorporate hydrophobic nanodomains.

Conclusions:

• Bilayer unzipping is an energetically favorable mechanism to accommodate hydrophobic blocks, avoiding acyl chain mismatch.
• This unzipping phenomenon provides new insights into biomembrane morphology changes induced by transmembrane proteins.
• Findings aid in programming the function of artificial hybrid membranes.