Cysteine-scanning mutagenesis of serotonin transporter intracellular loop 2 suggests an alpha-helical conformation.
Like other proteins involved in neurotransmitter transport, serotonin transporter (SERT) activity is regulated by multiple intracellular signal transduction pathways. The second intracellular loop (IL2) of SERT contains consensus sequences for cGMP-dependent protein kinase and protein kinase C. A 24-residue region of SERT including IL2, from Ile-270 through Ser-293, was analyzed by cysteine-scanning mutagenesis and chemical modification. 2-(Aminoethyl)methanethiosulfonate hydrobromide (MTSEA) failed to inhibit serotonin transport or binding of the cocaine analog 2beta-carbomethoxy-3beta-(4-[125I]iodophenyl)tropane (beta-CIT) in intact cells expressing these mutants, but it inactivated beta-CIT binding in membrane preparations. From the pattern of sensitivity, IL2 appears to extend from Trp-271 through Ile-290, a significantly longer region than that initially predicted by hydropathy analysis. Six mutants reacted with MTSEA much faster than the others, and the pattern of the more reactive mutations suggested that IL2 is in an alpha-helical conformation. Some of the mutants had significantly elevated transport rates, suggesting a possible mechanism for the regulation of SERT activity.
Zhang
Yuan-Wei
YW
Department of Pharmacology, Yale University School of Medicine, New Haven, Connecticut 06520-8066, USA.
Rudnick
Gary
G
D000595:Amino Acid Sequence; D000818:Animals; D003545:Cysteine / Q000378:metabolism*; D005020:Ethyl Methanesulfonate / Q000031:analogs & derivatives / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D007202:Indicators and Reagents / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism; D026901:Membrane Transport Proteins / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism; D008698:Mesylates / Q000378:metabolism; D008969:Molecular Sequence Data; D016296:Mutagenesis; D009419:Nerve Tissue Proteins / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism; D017433:Protein Structure, Secondary; D051381:Rats; D016415:Sequence Alignment; D012701:Serotonin / Q000378:metabolism; D050486:Serotonin Plasma Membrane Transport Proteins
D007202:Indicators and Reagents; D008562:Membrane Glycoproteins; D026901:Membrane Transport Proteins; D008698:Mesylates; D009419:Nerve Tissue Proteins; C493230:SLC6A4 protein, human; D050486:Serotonin Plasma Membrane Transport Proteins; C493232:Slc6a4 protein, rat; C093171:methanethiosulfonate ethylammonium; C109153:(2-sulfonatoethyl)methanethiosulfonate; D012701:Serotonin; D005020:Ethyl Methanesulfonate; D003545:Cysteine