2.A.66.1.10
Na -dependent cationic drug (ethidium, acriflavine, 2-N-methyl ellipticinium, berberine, norfloxacin, ciprofloxacin, rhodamine 6G, crystal violet, doxorubicin, novobiocin, enoxacin, and tetraphenylphosphonium chloride) efflux pump, NorM (Long et al. 2008).  3-d structures of the N. gonorrheae NorM transporter (96% identical to the N. miningitidis protein) have been solved complexed with three different substrates in a multidrug cavity and Cs (4HUN; Lu et al. 2013).  Lu et al. an identified 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, they observed a potential rearrangement of at least two transmembrane helices upon Na⁺-induced drug export. They suggested that Na⁺ triggers multidrug extrusion by inducing protein conformational changes rather than by directly competing for the substrate-binding amino acids.  However, see 2.A.66.1.32 where the opposite was concluded for a homologue that functions by drug:H⁺ antiport.