Poster abstracts

Poster number 73 submitted by Erik Hill

Cocaine analogs identify unique binding interactions with monoamine transporters

Erik R. Hill (Pharmacology - Ohio State University), Howard H. Gu (Pharmacology - Ohio State University)

Abstract:
Cocaine’s CNS effects are caused by inhibition of the neurotransmitter reuptake proteins; the dopamine transporter (DAT), the norepinephrine transporter (NET) and the serotonin transporter (SERT). DAT, NET, and SERT are highly hydrophobic integral membrane proteins with multiple conformations. This hampers modern protein structural analysis techniques, such as x-ray crystallography, and limits in situ discovery of cocaine binding sites. Since cocaine inhibits monoamine transporters at similar concentrations and these transporters share homology, it is presumed that they have a similar cocaine binding site. Cocaine analog compounds have been synthesized that contain chemical modifications to the cocaine structure. Many of these cocaine analog compounds are more potent inhibitors of the reuptake transporters than cocaine, presumably binding the same site as cocaine. However, despite transporter homology, some of the cocaine analogs have transporter-specific affinities, whereby these cocaine analogs inhibit DAT more potently than NET. Therefore, mutant reuptake transporters have been generated through positional mutagenesis of mouse monoamine transporters. These mutant proteins have switched specific dissimilar residues between mouse DAT and mouse NET that occur at the same protein sequence position. Residues identified for switching exist in putative transmembrane regions presumed to be in contact with the aqueous phase. Mutant proteins were tested with several transporter-specific cocaine analogs to identify regions and residues responsible for the transporter-specific potency. Applying in vitro data to an in silico design, these specific interactions can guide analogs into a transporter and generate a cocaine analog binding model. This analog binding model would suggest a possible cocaine binding site and will provide a testing ground for further biochemical experiments to confirm the interactions at the proposed cocaine binding site.

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Keywords: cocaine, structure function, transporter