MAS solid-state NMR studies on the multidrug transporter EmrE.

Area of Science:

• Biochemistry
• Structural Biology
• Biophysics

Background:

• The Escherichia coli multidrug resistance transporter EmrE is a key protein involved in expelling toxic compounds.
• Understanding EmrE's structure is crucial for developing strategies to combat multidrug resistance.
• Membrane proteins present unique challenges for structural studies due to their hydrophobic nature.

Purpose of the Study:

• To investigate the structure of the multidrug resistance transporter EmrE using magic-angle spinning (MAS) solid-state Nuclear Magnetic Resonance (NMR).
• To resolve the chemical shift of the critical amino acid E14 through selective experiments.
• To analyze the impact of the ligand tetraphenylphosphonium (TPP+) on EmrE's structure.

Main Methods:

• Utilizing uniformly 13C,15N isotopically enriched Escherichia coli EmrE.
• Employing MAS solid-state NMR spectroscopy, which allows study in a native-like membrane environment without detergents.
• Performing glutamic/aspartic acid selective experiments to assign the chemical shift of E14's carboxylic carbon.
• Comparing NMR spectra of wildtype EmrE with the EmrE-E14C mutant.
• Analyzing spectra in the presence and absence of the ligand TPP+.

Main Results:

• Successful assignment of the chemical shift for the carboxylic carbon of E14 in EmrE.
• Demonstration of solid-state NMR's capability to study membrane proteins in their native environment.
• Observation of spectral changes indicative of ligand binding (TPP+) to EmrE.
• Comparison of wildtype and mutant EmrE spectra providing insights into E14's role.

Conclusions:

• Solid-state NMR is a powerful technique for elucidating the structure of membrane proteins like EmrE in a lipid bilayer.
• The chemical shift of E14 has been successfully assigned, contributing to a detailed structural understanding of EmrE.
• Ligand binding of TPP+ induces conformational changes in EmrE, providing functional insights.