Tetra- and Penta-Cyclic Triterpenes Interaction with Lipid Bilayer Membrane: A Structural Comparative Study

Area of Science:

• Biochemistry
• Membrane Biophysics
• Lipid Chemistry

Background:

• Lipid bilayers form the fundamental structure of cell membranes.
• Triterpenes are natural compounds with diverse biological activities.
• Membrane fluidity is crucial for various cellular processes.

Purpose of the Study:

• To investigate the effects of tetracyclic and pentacyclic triterpenes (TTPs) on the fluidity of dipalmitoyl phosphatidyl choline (DPPC) liposome membranes.
• To elucidate the molecular mechanisms underlying TTP-membrane interactions.

Main Methods:

• Differential scanning calorimetry (DSC) to determine phase transition temperatures.
• Raman spectroscopy to probe molecular interactions within the lipid bilayer.
• Fluorescence polarization using 1,6-diphenyl-1,3,5-hexatriene (DPH) to assess membrane fluidity.

Main Results:

• TTPs abolished the pre-transition and modified Raman peaks, indicating interaction with phospholipid choline head groups.
• Increased disorder in alkyl chains and decreased main transition temperature confirmed TTPs' interaction with lipid acyl chains.
• Fluorescence depolarization showed that TTPs fluidize the liposomal membrane at various temperatures.
• Pentacyclic TTPs demonstrated a stronger fluidizing effect than tetracyclic TTPs, suggesting deeper bilayer incorporation.

Conclusions:

• Tetracyclic and pentacyclic triterpenes interact with both the head group and alkyl chains of DPPC liposomes.
• The hydrophobicity and polar head group of TTPs influence their incorporation into the lipid bilayer and their effect on membrane fluidity.
• Triterpenes can modulate membrane fluidity, with implications for their biological functions.