Molecular rationale for the impairment of the MexAB-OprM efflux pump by a single mutation in MexA

Area of Science:

• Microbiology
• Structural Biology
• Computational Biology

Background:

• Gram-negative pathogens utilize Resistance-Nodulation-cell Division (RND) superfamily efflux pumps to confer antibiotic resistance.
• These tripartite systems, comprising inner membrane transporter, outer membrane protein, and membrane fusion protein, expel diverse antibiotics.
• Multimerization of the membrane fusion protein is crucial for efflux pump function.

Purpose of the Study:

• Investigate the stability of MexA (a membrane fusion protein) dimers using computational methods.
• Provide a molecular explanation for how the G72S substitution impairs MexA assembly and MexAB-OprM efflux pump functionality.
• Understand how minor sequence changes induce significant conformational alterations in efflux pump components.

Main Methods:

• Employed complementary computational techniques.
• Conducted multiple microsecond-long molecular dynamics simulations.
• Analyzed the conformational equilibrium and stability of MexA protein and its mutants.

Main Results:

• MexA dimers were found to be stable across extensive molecular dynamics simulations.
• The G72S substitution significantly altered MexA's conformational equilibrium.
• The mutation favors a collapsed MexA conformation, hindering dimer and higher-order assembly formation.

Conclusions:

• MexA dimerization is stable, but the G72S mutation disrupts this essential assembly.
• Computational simulations reveal the mechanism by which single amino acid changes impact complex efflux pump systems.
• This study provides insights into targeting RND efflux pumps, a significant challenge in combating antibiotic resistance.