Cubic phases of lipid-containing systems. Structure analysis and biological implications

Area of Science:

• Materials Science
• Biophysics
• Crystallography

Background:

• Six cubic phases exist in lipid systems, but only two have known structures.
• Determining the structures of the remaining four cubic phases is crucial for understanding lipid organization.

Purpose of the Study:

• To determine the unambiguous structures of four previously uncharacterized cubic lipid phases.
• To develop and validate a novel pattern recognition approach for structure determination.

Main Methods:

• A novel pattern recognition approach was employed, generating all compatible phase angle sets (phi-sets).
• Two screening criteria, based on the [(delta rho)4] parameter, were used to identify the optimal phi-set: smoothness (minimum [(delta rho)4]) and thermodynamic similarity.
• The method was applied to analyze six cubic lipid phases.

Main Results:

• The structures of Q230, Q224, and Q229 were described as two intertwined 3D networks of connected rods with specific joining geometries (3x3, 4x4, 6x6).
• Structures of Q212 and Q227 were related to Q230 and Q224, respectively, with one rod network replaced by closed micelles.
• Q223 was characterized by a cage-like network of connected globules enclosing micelles.

Conclusions:

• The study successfully determined the structures of six cubic lipid phases using a novel pattern recognition method.
• The findings provide topological generalizations of bilayer and monolayer lipid organization paradigms.
• The identified structures show analogies with infinite periodic minimal surfaces, advancing the understanding of lipid self-assembly.