PT  - JOURNAL ARTICLE
AU  - Walter Sandtner
AU  - Thomas Stockner
AU  - Peter S. Hasenhuetl
AU  - John S. Partilla
AU  - Amir Seddik
AU  - Yuan-Wei Zhang
AU  - Jianjing Cao
AU  - Marion Holy
AU  - Thomas Steinkellner
AU  - Gary Rudnick
AU  - Michael H. Baumann
AU  - Gerhard F. Ecker
AU  - Amy Hauck Newman
AU  - Harald H. Sitte
TI  - Binding Mode Selection Determines the Action of Ecstasy Homologs at Monoamine Transporters
AID  - 10.1124/mol.115.101394
DP  - 2016 Jan 01
TA  - Molecular Pharmacology
PG  - 165--175
VI  - 89
IP  - 1
4099  - http://molpharm.aspetjournals.org/content/89/1/165.short
4100  - http://molpharm.aspetjournals.org/content/89/1/165.full
SO  - Mol Pharmacol2016 Jan 01; 89
AB  - Determining the structural elements that define substrates and inhibitors at the monoamine transporters is critical to elucidating the mechanisms underlying these disparate functions. In this study, we addressed this question directly by generating a series of N-substituted 3,4-methylenedioxyamphetamine analogs that differ only in the number of methyl substituents on the terminal amine group. Starting with 3,4-methylenedioxy-N-methylamphetamine, 3,4-methylenedioxy-N,N-dimethylamphetamine (MDDMA) and 3,4-methylenedioxy-N,N,N-trimethylamphetamine (MDTMA) were prepared. We evaluated the functional activities of the compounds at all three monoamine transporters in native brain tissue and cells expressing the transporters. In addition, we used ligand docking to generate models of the respective protein-ligand complexes, which allowed us to relate the experimental findings to available structural information. Our results suggest that the 3,4-methylenedioxyamphetamine analogs bind at the monoamine transporter orthosteric binding site by adopting one of two mutually exclusive binding modes. 3,4-methylenedioxyamphetamine and 3,4-methylenedioxy-N-methylamphetamine adopt a high-affinity binding mode consistent with a transportable substrate, whereas MDDMA and MDTMA adopt a low-affinity binding mode consistent with an inhibitor, in which the ligand orientation is inverted. Importantly, MDDMA can alternate between both binding modes, whereas MDTMA exclusively binds to the low-affinity mode. Our experimental results are consistent with the idea that the initial orientation of bound ligands is critical for subsequent interactions that lead to transporter conformational changes and substrate translocation.