title: A human serotonin transporter mutation causes constitutive activation of transport activity.
abstract: A rarely occurring variant of human serotonin transporter (hSERT) was tested for its functional consequences in HeLa and COS-7 cells. The variant, in which Ile-425 is converted to Val, was significantly different from wild type with respect to its catalytic properties. In both cell types, rates of serotonin (5-HT) transport were higher for the I425V variant. Both an increase in Vmax and a decrease in KM caused this increase in rate. The increase in Vmax was not accounted for by increases in transporter expression or in the distribution of transporter between the cell surface and intracellular pools. The decrease in KM was accompanied by a decrease in the KD for binding of the cocaine analog 2beta-carbomethoxy-3beta-(4-[125I]iodophenyl)tropane. In both HeLa and COS-7 cells, the nitric oxide donor S-nitroso-N-acetylpenicillamine increased the activity of wild-type hSERT to that of the variant but did not change the activity of the I425V variant. This stimulation was prevented by the presence of oxyhemoglobin, which quenches nitric oxide, and by an inhibitor of guanylyl cyclase.
authors.affiliation: Department of Pharmacology, Yale University School of Medicine, 333 Cedar Street, P.O. Box 208066, New Haven, CT 06520-8066, USA.
authors.forename: Fusun
authors.initials: F
authors.lastname: Kilic
authors.forename: Dennis L
authors.initials: DL
authors.lastname: Murphy
authors.forename: Gary
authors.initials: G
authors.lastname: Rudnick
mesh_terms: D019943:Amino Acid Substitution; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D019921:Biotinylation; D019556:COS Cells; D002352:Carrier Proteins / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D007150:Immunohistochemistry; D007532:Isoleucine / Q000235:genetics; D007700:Kinetics; D008562:Membrane Glycoproteins / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D026901:Membrane Transport Proteins; D016297:Mutagenesis, Site-Directed; D009419:Nerve Tissue Proteins; D020030:Nitric Oxide Donors / Q000494:pharmacology; D012701:Serotonin / Q000378:metabolism*; D050486:Serotonin Plasma Membrane Transport Proteins; D014162:Transfection; D014633:Valine / Q000235:genetics
chemical_list: D002352:Carrier Proteins; D008562:Membrane Glycoproteins; D026901:Membrane Transport Proteins; D009419:Nerve Tissue Proteins; D020030:Nitric Oxide Donors; C493230:SLC6A4 protein, human; D050486:Serotonin Plasma Membrane Transport Proteins; D007532:Isoleucine; D012701:Serotonin; D014633:Valine