Multimeric forms of the small multidrug resistance protein EmrE in anionic detergent

Area of Science:

• Biochemistry
• Molecular Biology
• Structural Biology

Background:

• Escherichia coli multidrug resistance protein E (EmrE) is a key transporter in the small multidrug resistance family.
• EmrE confers resistance to quaternary cation compounds (QCC) using proton motive force.
• EmrE's multimeric state is dynamic and condition-dependent.

Purpose of the Study:

• To investigate the multimerization of EmrE in sodium dodecyl sulphate (SDS).
• To determine the influence of protein concentration and tetraphenyl phosphonium (TPP) on EmrE structure.
• To elucidate the conformational changes of EmrE during substrate binding.

Main Methods:

• Solubilization of EmrE in SDS at varying concentrations.
• SDS-Tricine polyacrylamide gel electrophoresis (PAGE) to analyze multimerization.
• Small angle neutron scattering (SANS) to determine multimer shapes.
• Circular dichroism (CD) and fluorescence spectroscopy for structural and residue analysis.

Main Results:

• EmrE exists as monomers at low SDS concentrations and forms various multimers at higher concentrations.
• Tetraphenyl phosphonium (TPP) addition enhances EmrE multimer formation.
• SANS revealed conformational changes in EmrE dimers and larger multimers upon TPP addition.
• Spectroscopic analyses showed susceptibility of aromatic residues to SDS concentration and ligand binding.

Conclusions:

• EmrE exhibits concentration-dependent multimerization in SDS.
• Substrate (TPP) binding influences EmrE's quaternary structure and conformation.
• These findings provide insights into the mechanism of multidrug resistance mediated by EmrE.