Visualizing a multidrug resistance protein, EmrE, with major bacterial lipids using Brewster angle microscopy

Area of Science:

• Membrane biophysics
• Microbial drug resistance mechanisms
• Protein-lipid interactions

Background:

• Lipid-protein interactions are crucial for understanding membrane architecture and developing new therapeutics against drug-resistant microbes.
• Escherichia coli's inner membrane multidrug resistance protein, EmrE, requires multimerization for function, which is challenging to study in vivo.

Purpose of the Study:

• To investigate the influence of major Escherichia coli lipids (phosphatidylethanolamine, phosphatidylglycerol, cardiolipin) on the multidrug resistance protein EmrE.
• To determine how variations in lipid head group, acyl chain length, and saturation affect lipid-protein associations with EmrE.

Main Methods:

• Utilized Langmuir monolayers to study lipid behavior.
• Employed Brewster angle microscopy to visualize lipid-protein interactions and membrane packing.
• Investigated three key E. coli lipids with varying properties in the presence and absence of EmrE.

Main Results:

• Lipid head group, acyl chain length, and saturation significantly impacted membrane packing and EmrE associations.
• EmrE most strongly influenced long unsaturated anionic lipids.
• Cardiolipin with longer unsaturated acyl chains formed the most stable monolayer with EmrE, suggesting hydrophobic matching stabilizes protein structure.

Conclusions:

• Lipid acyl chain length and saturation are critical determinants of EmrE's interaction and clustering behavior.
• Hydrophobic matching between cardiolipin acyl chains and EmrE's helical structure appears to stabilize the protein.
• These findings provide insights into membrane protein function and potential therapeutic strategies against microbial drug resistance.