Transmembrane domain I contributes to the permeation pathway for serotonin and ions in the serotonin transporter.

Barker EL, Moore KR, Rakhshan F, Blakely RD
J Neurosci. 1999 19 (12): 4705-17

PMID: 10366604 · PMCID: PMC6782662

Mutation of a conserved Asp (D98) in the rat serotonin (5HT) transporter (rSERT) to Glu (D98E) led to decreased 5HT transport capacity, diminished coupling to extracellular Na+ and Cl-, and a selective loss of antagonist potencies (cocaine, imipramine, and citalopram but not paroxetine or mazindol) with no change in 5HT Km value. D98E, which extends the acidic side chain by one carbon, affected the rank-order potency of substrate analogs for inhibition of 5HT transport, selectively increasing the potency of two analogs with shorter alkylamine side chains, gramine, and dihydroxybenzylamine. D98E also increased the efficacy of gramine relative to 5HT for inducing substrate-activated currents in Xenopus laevis oocytes, but these currents were noticeably dependent on extracellular medium acidification. I-V profiles for substrate-independent and -dependent currents indicated that the mutation selectively impacts ion permeation coupled to 5HT occupancy. The ability of the D98E mutant to modulate selective aspects of substrate recognition, to perturb ion dependence as well as modify substrate-induced currents, suggests that transmembrane domain I plays a critical role in defining the permeation pathway of biogenic amine transporters.

MeSH Terms (34)

Adrenergic Uptake Inhibitors Alkaloids Amino Acid Substitution Animals Aspartic Acid Biological Transport Calcium-Binding Proteins Calnexin Carrier Proteins Cocaine COS Cells HeLa Cells Humans Imipramine Intracellular Membranes Iodine Radioisotopes Ion Channel Gating Membrane Glycoproteins Membrane Potentials Membrane Transport Proteins Molecular Sequence Data N,N-Dimethyltryptamine Nerve Tissue Proteins Oocytes Protein Structure, Tertiary Rats Sequence Homology, Amino Acid Serotonin Serotonin Plasma Membrane Transport Proteins Serotonin Receptor Agonists Sodium Chloride Transfection Tritium Xenopus

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