pH-Driven Self-Assembly of Acidic Microbial Glycolipids

Area of Science:

• Biochemistry
• Materials Science
• Supramolecular Chemistry

Background:

• Microbial glycolipids are known compounds, but their self-assembly in water remains poorly understood.
• Their amphipathic nature, with a hydrophilic sugar head and hydrophobic fatty acid tail, presents complex self-assembly challenges.
• Stimuli-responsive properties are linked to the free carboxylic acid end group, but predictability is low.

Purpose of the Study:

• To investigate the aqueous self-assembly behavior of β-d-glucose microbial glycolipids with varying fatty acid chains.
• To elucidate the factors influencing the self-assembly structures formed by these glycolipids.
• To understand the role of membrane elasticity and pH in dictating self-assembly morphology.

Main Methods:

• Cryo-transmission electron microscopy (cryo-TEM) for structural visualization.
• pH-dependent in situ and ex situ small-angle X-ray scattering (SAXS) for structural analysis.
• Utilizing a "pH-jump" process to study dynamic self-assembly.

Main Results:

• Aqueous self-assembly of β-d-glucose glycolipids with saturated and monounsaturated C18 fatty acids could not be explained by the simple packing parameter model.
• Glycolipids with monounsaturated fatty acids formed vesicles below pH 6.2.
• Glycolipids with saturated fatty acids formed infinite bilayer sheets below pH 7.8, deviating from expected vesicle formation.
• Disaccharide-containing cellobioselipid predominantly formed chiral fibers instead of micelles.

Conclusions:

• Bilayer membrane elasticity, influenced by temperature relative to the lipid's melting point (TM), is crucial for determining self-assembly structures (sheets vs. vesicles).
• The fatty acid chain saturation significantly impacts the pH-dependent self-assembly and resulting morphology.
• The packing parameter alone is insufficient to predict the complex self-assembly of these microbial glycolipids.