Multidrug Efflux Mechanisms in Gram-Negative Bacteria

Gram-negative bacteria deploy sophisticated efflux systems to expel chemically diverse antimicrobial agents, underpinning a major form of multidrug resistance. Central to this defence are Resistance-Nodulation-Division (RND) pumps, which assemble as tripartite complexes spanning the inner membrane, periplasm and outer membrane. An inner membrane transporter captures substrates from the cytoplasm or periplasm, relays them via a periplasmic adaptor protein and discharges them through an outer membrane channel. Other transporter families, including Major Facilitator Superfamily (MFS), ATP-binding Cassette (ABC), Multidrug and Toxic compound Extrusion (MATE) and Small Multidrug Resistance (SMR), contribute additional efflux capacities. The structural dynamics of these assemblies, their regulatory circuits and the interplay with membrane permeability barriers govern both intrinsic and acquired resistance. Efflux pumps also affect bacterial physiology, biofilm formation and virulence, making them prime targets for inhibitor development. Recent advances in structural biology, genetics and medicinal chemistry have begun to reveal allosteric inhibition sites, mutation-driven specificity shifts and ecological distribution patterns, offering new avenues to counteract efflux-mediated resistance on a global scale.

Research from Nature Portfolio

Recent studies have defined the molecular basis of efflux adaptor inhibition. Detailed mass-spectrometry and molecular-dynamics analyses revealed that a small-molecule inhibitor wedges between distinct domains of the periplasmic adaptor protein, stabilising its conformation and blocking signal transmission from the inner transporter to the outer channel. This allosteric mechanism attenuates pump function and suggests a blueprint for adaptor-targeted therapeutics. In parallel, high-resolution electron-microscopy reconstructions of native tripartite complexes reconstituted in lipid nanodiscs demonstrated that inner and outer membrane components self-assemble via the periplasmic adaptor, forming a continuous exit duct without direct membrane contacts. These data underscore a conserved assembly pathway and identify the adaptor interface as a strategic locus for future inhibitory interventions.

Multidrug Efflux Mechanisms in Gram-Negative Bacteria publication trend

The graph below shows the total number of articles in multidrug efflux mechanisms in gram-negative bacteria across all publications each year (not limited to Nature Index journals).

Technical terms

Resistance-Nodulation-Division (RND) efflux pump: A tripartite transporter family that spans both membranes in Gram-negative bacteria, actively exporting diverse substrates.

Periplasmic adaptor protein: A bridging component that connects the inner membrane transporter to the outer membrane channel, forming the continuous efflux conduit.

Outer membrane channel (TolC family): A trans-envelope pore through which substrates exit the cell.

Efflux pump inhibitor (EPI): A compound that binds to pump components, reducing drug export and restoring antibiotic susceptibility.

Substrate binding pocket: The region within the transporter where antibiotics or other compounds are recognised and engaged for export.

References

1. Conformational restriction shapes the inhibition of a multidrug efflux adaptor protein. Nature Communications (2023).
2. Functionally distinct mutations within AcrB underpin antibiotic resistance in different lifestyles. npj Antimicrobials and Resistance (2023).
3. Pyridylpiperazine efflux pump inhibitor boosts in vivo antibiotic efficacy against K. pneumoniae. EMBO Molecular Medicine (2023).
4. HME, NFE, and HAE-1 efflux pumps in Gram-negative bacteria: a comprehensive phylogenetic and ecological approach. ISME Communications (2024).
5. Synergy between Active Efflux and Outer Membrane Diffusion Defines Rules of Antibiotic Permeation into Gram-Negative Bacteria. mBio (2017).
6. Tripartite assembly of RND multidrug efflux pumps. Nature Communications (2016).