Coupling between sterol and sphingolipid structure in ordered membrane domains

Area of Science:

• Biochemistry
• Cell Biology
• Membrane Biophysics

Background:

• Eukaryotic membranes feature specific sterol-sphingolipid pairings, like cholesterol-sphingomyelin in mammals and ergosterol-very long-chain sphingolipids in fungi.
• These lipid classes are thought to co-evolve for membrane structure and organization.

Purpose of the Study:

• Investigate how sterol structure and sphingolipid chain length jointly control membrane order and phase behavior.
• Determine the physical basis for observed lipid-dependent membrane organization.

Main Methods:

• Studied the yeast Saccharomyces cerevisiae to observe effects of lipid composition on vacuole membrane domains.
• Utilized synthetic membranes with defined compositions of ergosterol or cholesterol and sphingomyelin of varying chain lengths.
• Measured membrane order and phase behavior in response to lipid composition.

Main Results:

• Loss of very long-chain sphingolipids or substitution of ergosterol for cholesterol disrupted liquid-ordered (L_o) domains in yeast vacuole membranes.
• In synthetic membranes, ergosterol sparsely supported L_o domains with C16 sphingomyelin, unlike cholesterol.
• C26 sphingomyelin membranes showed distinct phase behavior with ergosterol, creating a window for fluid domains relevant to nutritional restriction responses.

Conclusions:

• Sphingolipid chain length modulates sterol interactions, influencing membrane organization.
• The findings provide insights into the physical basis of sterol-sphingolipid co-evolution for membrane structure.
• This work connects lipid composition to membrane phase separation relevant to cellular adaptation.