Sphingomyelin slows interfacial hydrogen-bonding dynamics in lipid membranes

Area of Science:

• Biophysics
• Membrane Biophysics
• Computational Biophysics

Background:

• Interfacial hydrogen bonding (H-bonding) is crucial for membrane structure, heterogeneity, and dynamics.
• Understanding how lipid composition influences lipid-lipid interactions and H-bond dynamics is essential due to the chemical diversity of lipids.

Purpose of the Study:

• To investigate the role of palmitoyl sphingosylphosphorylcholine (PSM) in modulating lipid H-bond networks.
• To examine the combined effects of PSM and dipalmitoyl phosphatidylcholine (DPPC) on H-bond populations and dynamics.

Main Methods:

• Ultrafast two-dimensional infrared (2D IR) spectroscopy.
• Molecular dynamics simulations.

Main Results:

• Composition-dependent H-bond ensembles were observed for ester and amide carbonyls.
• Increased PSM concentrations led to higher H-bond populations and slower dynamics.
• PSM acts as an H-bond donor, replacing water-mediated interactions and forming direct lipid-lipid H-bonds (up to 20%), which stabilize networks and slow interfacial dynamics by 45% in equimolar mixtures.

Conclusions:

• PSM plays a dual role in H-bonding, increasing membrane viscosity and stabilizing lipid interfaces.
• The study provides molecular insights into the function of sphingolipids in cell membranes.
• The synergy of experimental and computational methods is highlighted for studying complex membrane interactions.