Multidrug resistance is a serious threat to public health. Proton motive force-driven antiporters from the major facilitator superfamily (MFS) constitute a major group of multidrug-resistance transporters. Currently, no reports on crystal structures of MFS antiporters in complex with their substrates exist. The E. coli MdfA transporter is a well-studied model system for biochemical analyses of multidrug-resistance MFS antiporters. Here, we report three crystal structures of MdfA-ligand complexes at resolutions up to 2.0 ?, all in the inward-facing conformation. The substrate-binding site sits proximal to the conserved acidic residue, D34. Our mutagenesis studies support the structural observations of the substrate-binding mode and the notion that D34 responds to substrate binding by adjusting its protonation status. Taken together, our data unveil the substrate-binding mode of MFS antiporters and suggest a mechanism of transport via this group of transporters.
Prokaryotic expression system (E.coli expression system) is a classical expression system developed earlier and widely used in gene expression technology. In recent decades, E.coli expression system has been continuously developed and improved, and has been widely used by scientific research and industrial users to express various recombinant proteins. Compared with other expression systems, it is characterized by high expression level of target gene, short culture period, strong anti-pollution ability and low cost. Our researchers have established a mature E.coli expression service platform to provide the expression and purification of various recombinant proteins and their complexes in escherichia coli.
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