Cell Research 2015-09-01

Substrate-bound structure of the E. coli multidrug resistance transporter MdfA.

Jie Heng, Yan Zhao, Ming Liu, Yue Liu, Junping Fan, Xianping Wang, Yongfang Zhao, Xuejun C Zhang

Index: Cell Res. 25 , 1060-73, (2015)

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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.