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Quantification of Membrane Protein Conformational Free Energy from Mutations and a Single Atom
Belen Ramirez-Cordero1, Nathaniel J Traaseth1
1Department of Chemistry, New York University, New York, New York 10003, United States.
Journal of the American Chemical Society
|September 15, 2025
Summary
Researchers quantified free energy differences in the E. coli multidrug transporter EmrE using 19F NMR. Subtle changes, like single mutations or fluorine atoms, significantly altered transporter conformations and their energy landscapes.
Area of Science:
- Biochemistry
- Structural Biology
- Biophysics
Background:
- Secondary active transporters are crucial membrane proteins facilitating cellular transport.
- Their function relies on dynamic conformational changes between distinct states (inward- and outward-facing).
- Quantifying the free energy differences between these states is vital for understanding transport mechanisms but remains underexplored.
Purpose of the Study:
- To quantify the free energy differences between inward- and outward-facing conformations of the multidrug transporter EmrE from E. coli.
- To investigate the impact of subtle molecular modifications on transporter conformational equilibrium.
Main Methods:
- Utilized 19F Nuclear Magnetic Resonance (NMR) spectroscopy.
- Employed a minimal heterodimer of EmrE, introducing a single mutation into one monomer.
- Measured perturbations in the conformational equilibrium between inward- and outward-facing states.
Main Results:
- A single conservative mutation altered the conformational equilibrium by up to 1.5 kcal/mol.
- The introduction of a single fluorine atom influenced the equilibrium by up to 0.8 kcal/mol.
- Demonstrated that subtle changes significantly impact the free energy landscape of EmrE.
Conclusions:
- Subtle molecular alterations can profoundly influence the conformational free energy landscape of secondary active transporters.
- This suggests inherent plasticity in transporters that may play a role in evolutionary adaptation.
- Provides quantitative insights into transporter dynamics and conformational regulation.
