Long and short lipid molecules experience the same interleaflet drag in lipid bilayers

Area of Science:

• Biophysics
• Materials Science
• Cell Biology

Background:

• Membrane interleaflet viscosity (ηe) plays a crucial role in various cell membrane phenomena, including tether formation, domain formation, cell shape changes, and budding.
• Interdigitation of lipid chains between opposing monolayers is often considered a significant contributor to interleaflet coupling.

Purpose of the Study:

• To investigate the relationship between lipid chain length and membrane interleaflet viscosity (ηe).
• To determine the contribution of lipid patch sliding to interleaflet friction and compare it with expected contributions from interdigitation.

Main Methods:

• Utilized fluorescent lipid analogues of varying chain lengths to probe membrane properties.
• Measured the friction experienced by lipid analogues at the ends of monolayers to determine interleaflet viscosity (ηe).
• Assessed the translational diffusion coefficient of lipids to understand in-layer viscosity.

Main Results:

• The membrane interleaflet viscosity (ηe) was found to be approximately 3×10^9 J s m^-4 for both short and long chain lipid analogues.
• Contrary to expectations, the sliding of lipid patches between opposing monolayers determined ηe, rather than interdigitation.
• In-layer viscosity, while dependent on lipid length, was significantly lower than the measured interleaflet viscosity (ηe).

Conclusions:

• Lipid patch sliding is a dominant factor in membrane interleaflet viscosity, and its contribution is largely independent of lipid chain length.
• The measured interleaflet viscosity (ηe) is substantially higher than the in-layer viscosity, highlighting distinct mechanical properties of the membrane.
• These findings provide a refined understanding of membrane mechanics and lipid-lipid interactions within cellular membranes.