Conformational dynamics of the MdfA multidrug efflux pump and structural mechanisms underlying substrate efflux: A...

The multidrug efflux pump MdfA, a prototypical member of the Major Facilitator Superfamily (MFS), plays a pivotal role in antibiotic resistance in Escherichia coli by exporting a remarkably broad spectrum of structurally diverse compounds. Despite extensive structural characterization, a unified mechanistic framework linking MdfA's conformational dynamics to substrate recognition and proton-coupled antiport remains incomplete. In this review, we synthesize current knowledge on MdfA with a focus on the conformational transitions underlying multidrug efflux. We compare available inward- and outward-facing structures and critically assess representative models of conformational change in MFS transporters. Experimental evidence from crystallography, mutagenesis, and biophysical assays is integrated with molecular dynamics simulations and AI-assisted structural predictions to capture functional motions beyond static structures. In addition, analysis of known substrates and inhibitors reveals conserved elements essential for proton coupling and variable regions enabling substrate polyspecificity. We further discuss how insights into MdfA's conformational landscape inform emerging strategies for efflux pump inhibition and multidrug resistance. Collectively, this review establishes a mechanistically unified framework that links structure, dynamics, and function, providing generalizable principles for understanding and targeting multidrug transporters across the MFS family.