Assessing Interactions Between a Polytopic Membrane Protein and Lipid Bilayers Using Differential Scanning...

Area of Science:

• Biochemistry
• Biophysics
• Membrane Biology

Background:

• Cellular membrane lipid composition influences membrane protein structure and function.
• Understanding these interactions is crucial for deciphering cellular transport mechanisms.

Purpose of the Study:

• Investigate how structural changes in the secondary active drug transporter EmrE upon substrate binding affect the lipid bilayer.
• Elucidate the relationship between protein conformational changes and lipid dynamics.

Main Methods:

• Reconstitution of EmrE into phospholipid bilayers with varying lipid properties.
• Differential scanning calorimetry (DSC) to analyze lipid phase transitions.
• Solid-state Nuclear Magnetic Resonance (NMR) spectroscopy (magic-angle spinning and oriented) to probe lipid and protein environments.

Main Results:

• DSC revealed altered lipid phase transition cooperativity between drug-free and drug-bound EmrE.
• ³¹P NMR showed reduced lipid line widths around the phase transition upon TPP⁺ binding.
• Oriented solid-state NMR indicated chemical shift perturbations in EmrE residues upon TPP⁺ binding.

Conclusions:

• Substrate binding induces structural and dynamic changes in EmrE.
• These protein dynamics alterations directly impact the surrounding lipid bilayer.
• A mechanism is proposed where substrate-induced EmrE structural changes modulate lipid bilayer properties.