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1. chinaXiv:201605.01368 [pdf]

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

Heng, Jie; Zhao, Yan; Liu, Yue; Fan, Junping; Wang, Xianping; Zhao, Yongfang; Zhang, Xuejun C.; Heng, Jie; Zhao, Yan; Liu, Ming
Subjects: Biology >> Biophysics >> Cell Biology

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 angstrom, 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.

submitted time 2016-05-12 Hits521Downloads295 Comment 0

2. chinaXiv:201605.01350 [pdf]

Energy coupling mechanisms of MFS transporters

Zhang, Xuejun C.; Zhao, Yan; Heng, Jie; Jiang, Daohua
Subjects: Biology >> Biophysics >> Biochemistry & Molecular Biology

Major facilitator superfamily (MFS) is a large class of secondary active transporters widely expressed across all life kingdoms. Although a common 12-transmembrane helix-bundle architecture is found in most MFS crystal structures available, a common mechanism of energy coupling remains to be elucidated. Here, we discuss several models for energy-coupling in the transport process of the transporters, largely based on currently available structures and the results of their biochemical analyses. Special attention is paid to the interaction between protonation and the negative-inside membrane potential. Also, functional roles of the conserved sequence motifs are discussed in the context of the 3D structures. We anticipate that in the near future, a unified picture of the functions of MFS transporters will emerge from the insights gained from studies of the common architectures and conserved motifs.

submitted time 2016-05-11 Hits414Downloads277 Comment 0

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