Evidence for a two-dimensional molecular lattice in subgel phase DPPC bilayers

Area of Science:

• Biophysics
• Materials Science
• Lipid Bilayer Research

Background:

• Understanding lipid packing and phase behavior is crucial for membrane biophysics.
• The subgel phase of phospholipids like DPPC exhibits complex molecular ordering.
• Previous studies have suggested ordered structures in DPPC phases, but precise lattice details remained elusive.

Purpose of the Study:

• To elucidate the molecular arrangement and lattice structure of 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC) in its subgel phase.
• To reconcile existing X-ray diffraction data with a definitive structural model.
• To provide insights into lipid molecule correlations within and between bilayers.

Main Methods:

• X-ray diffraction analysis of oriented DPPC films.
• X-ray diffraction analysis of multilamellar liposomes of DPPC.
• Analysis of data in the context of lipid molecular packing and phase behavior.

Main Results:

• Established the presence of a 2D molecular lattice in the DPPC subgel phase.
• The lattice structure comprises two lipid molecules and is consistent with all available literature data.
• DPPC molecules are ordered in the bilayer plane and positionally correlated within a single bilayer.
• No positional correlation was observed between DPPC molecules in adjacent bilayers.

Conclusions:

• The proposed 2D lattice model accurately describes the subgel phase of DPPC.
• This finding advances the understanding of lipid organization in ordered membrane phases.
• The study provides a structural basis for the observed physical properties of DPPC in the subgel phase.