title: Structures of a Na+-coupled, substrate-bound MATE multidrug transporter.
abstract: Multidrug transporters belonging to the multidrug and toxic compound extrusion (MATE) family expel dissimilar lipophilic and cationic drugs across cell membranes by dissipating a preexisting Na(+) or H(+) gradient. Despite its clinical relevance, the transport mechanism of MATE proteins remains poorly understood, largely owing to a lack of structural information on the substrate-bound transporter. Here we report crystal structures of a Na(+)-coupled MATE transporter NorM from Neisseria gonorrheae in complexes with three distinct translocation substrates (ethidium, rhodamine 6G, and tetraphenylphosphonium), as well as Cs(+) (a Na(+) congener), all captured in extracellular-facing and drug-bound states. The structures revealed a multidrug-binding cavity festooned with four negatively charged amino acids and surprisingly limited hydrophobic moieties, in stark contrast to the general belief that aromatic amino acids play a prominent role in multidrug recognition. Furthermore, we discovered an uncommon cation-π interaction in the Na(+)-binding site located outside the drug-binding cavity and validated the biological relevance of both the substrate- and cation-binding sites by conducting drug resistance and transport assays. Additionally, we uncovered potential rearrangement of at least two transmembrane helices upon Na(+)-induced drug export. Based on our structural and functional analyses, we suggest that Na(+) triggers multidrug extrusion by inducing protein conformational changes rather than by directly competing for the substrate-binding amino acids. This scenario is distinct from the canonical antiport mechanism, in which both substrate and counterion compete for a shared binding site in the transporter. Collectively, our findings provide an important step toward a detailed and mechanistic understanding of multidrug transport.
authors: Department of Biochemistry and Molecular Biology, Rosalind Franklin University of Medicine and Science, North Chicago, IL 60064, USA. min.lu@rosalindfranklin.edu
authors: Min
authors: M
authors: Lu
authors: Jindrich
authors: J
authors: Symersky
authors: Martha
authors: M
authors: Radchenko
authors: Akiko
authors: A
authors: Koide
authors: Yi
authors: Y
authors: Guo
authors: Rongxin
authors: R
authors: Nie
authors: Shohei
authors: S
authors: Koide
mesh_terms: D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D017920:Antiporters / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites; D002586:Cesium / Q000378:metabolism; D018360:Crystallography, X-Ray; D024901:Drug Resistance, Multiple, Bacterial / Q000235:genetics; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009344:Neisseria gonorrhoeae / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D011487:Protein Conformation; D017386:Sequence Homology, Amino Acid; D012964:Sodium / Q000378:metabolism; D055672:Static Electricity
chemical_list: D017920:Antiporters; D001426:Bacterial Proteins; C114619:NorM protein, bacteria; D002586:Cesium; D012964:Sodium