Structural Analysis of the Extracellular Entrance to the Serotonin Transporter Permeation Pathway

Overview

Journal J Biol Chem

Specialty Biochemistry

Date 2010 Mar 23

PMID 20304925

Citations 4

Authors

Melissa I Torres-Altoro

Charles P Kuntz

David E Nichols

Eric L Barker

Affiliations

Soon will be listed here.

Abstract

Neurotransmitter transporters are responsible for removal of biogenic amine neurotransmitters after release into the synapse. These transporters are the targets for many clinically relevant drugs, such as antidepressants and psychostimulants. A high resolution crystal structure for the monoamine transporters has yet to be solved. We have developed a homology model for the serotonin transporter (SERT) based on the crystal structure of the leucine transporter (LeuT(Aa)) from Aquifex aeolicus. The objective of the present studies is to identify the structural determinants forming the entrance to the substrate permeation pathway based on predictions from the SERT homology model. Using the substituted cysteine accessibility method, we identified residues predicted to reside at the entrance to the substrate permeation pathway that were reactive with methanethiosulfonate (MTS) reagents. Of these residues, Gln(332) in transmembrane helix (TMH) VI was protected against MTS inactivation in the presence of serotonin. Surprisingly, the reactivity of Gln(332) to MTS reagents was enhanced in the presence of cocaine. Bifunctional MTS cross-linkers also were used to examine the distances between helices predicted to form the entrance into the substrate and ion permeation pathway. Our studies suggest that substrate and ligand binding may induce conformational shifts in TMH I and/or VI, providing new opportunities to refine existing homology models of SERT and related monoamine transporters.

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