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Reconstructing a Chloride-binding Site in a Bacterial Neurotransmitter Transporter Homologue

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Forrest,  Lucy R.
Max Planck Research Group of Computational Structural Biology, Max Planck Institute of Biophysics, Max Planck Society;

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Citation

Tavoulari, S., Rizwan, A. N., Forrest, L. R., & Rudnick, G. (2011). Reconstructing a Chloride-binding Site in a Bacterial Neurotransmitter Transporter Homologue. The Journal of Biological Chemistry, 286(4), 2834-2842.


Cite as: http://hdl.handle.net/11858/00-001M-0000-0024-D617-E
Abstract
In ion-coupled transport proteins, occupation of selective ion-binding sites is required to trigger conformational changes that lead to substrate translocation. Neurotransmitter transporters, targets of abused and therapeutic drugs, require Na+ and Cl for function. We recently proposed a chloride-binding site in these proteins not present in Cl-independent prokaryotic homologues. Here we describe conversion of the Cl-independent prokaryotic tryptophan transporter TnaT to a fully functional Cl-dependent form by a single point mutation, D268S. Mutations in TnaT-D268S, in wild type TnaT and in serotonin transporter provide direct evidence for the involvement of each of the proposed residues in Cl coordination. In both SERT and TnaT-D268S, Cl and Na+ mutually increased each other's potency, consistent with electrostatic interaction through adjacent binding sites. These studies establish the site where Cl binds to trigger conformational change during neurotransmitter transport.