Acyl-chain mismatch driven superlattice arrangements in DPPC/DLPC/cholesterol bilayers

Area of Science:

• Biophysics
• Membrane Biology
• Physical Chemistry

Background:

• Lipid acyl chain length mismatch is a key factor in membrane organization.
• Understanding lipid lateral organization is crucial for membrane function and homeostasis.
• The Superlattice (SL) model predicts specific lipid arrangements in bilayers.

Purpose of the Study:

• To investigate the effect of phosphatidylcholine (PC) acyl chain length mismatch on lipid lateral organization.
• To explore the formation of lipid superlattices in dipalmitoyl-PC/dilauroyl-PC/cholesterol bilayers.
• To elucidate the implications of these arrangements for eukaryote membrane homeostasis.

Main Methods:

• Utilized fluorescence and infrared spectroscopy.
• Employed cholesterol oxidase activity assays.
• Performed steady-state and time-resolved fluorescence anisotropy measurements of diphenylhexatriene-labeled PC (DPH-PC).

Main Results:

• Observed significant peaks in DPH-PC anisotropy and dips/peaks in vibrational frequencies at specific lipid compositions, coinciding with SL model predictions.
• Identified a prominent peak in anisotropy at a specific cholesterol/DPPC mole fraction, suggesting simultaneous CHOL/PC and DPPC/DLPC superlattices.
• Time-resolved measurements confirmed an ordered, rotationally hindered acyl chain environment at critical compositions, consistent with SL arrangements.

Conclusions:

• Demonstrated the parallel presence of CHOL/PC and DPPC/DLPC superlattices in mixed lipid bilayers.
• Proposed that DPPC and DLPC adopt SL-like distributions, facilitating head group and acyl chain mobility.
• Highlighted the significant implications of these coexisting superlattices for lipid homeostasis in eukaryotic membranes.