Substrate-bound structure of the E. coli multidrug resistance transporter MdfA
Heng, J., Zhao, Y., Liu, M., Liu, Y., Fan, J., Wang, X., Zhao, Y., Zhang, X.C.(2015) Cell Res 25: 1060-1073
- PubMed: 26238402 
- DOI: https://doi.org/10.1038/cr.2015.94
- Primary Citation of Related Structures:  
4ZOW, 4ZP0, 4ZP2 - PubMed Abstract: 
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 Å, 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.
Organizational Affiliation: 
National Laboratory of Macromolecules, National Center of Protein Science-Beijing, Institute of Biophysics, Chinese Academy of Sciences, 15 Datun Road, Beijing 100101, China.