title: Characterization of Thr-354 in the human sodium/iodide symporter (NIS) by site-directed mutagenesis.
abstract: Sodium/iodide symporter (NIS) is the key molecule concentrating iodide in the thyroid gland. The first-described human NIS (hNIS) mutation to cause a complete iodide transport defect was the T354P mutation. The Thr-354 lies in the midst of the putative ninth transmembrane segment which is well-conserved within the members of the SLC5A transporter family. Here we have investigated the molecular function of Thr-354 using site-directed mutagenesis and found that T354S and T354A mutations result in significantly decreased iodide transport activity, 50 % and 2 % of wild-type hNIS. Our findings indicate that whereas Thr-354 is indispensable for the complete NIS activity, the β-hydroxyl group accounts for half, and the α-helical structure alone contributes for one-fiftieth of wild-type hNIS activity.
authors.affiliation: Department of Laboratory Medicine, Osaka University Graduate School of Medicine, Suita-shi Yamada-oka 2-2-D2, Osaka, Japan. tatsumi@labo.med.osaka-u.ac.jp
authors.forename: Ke-ita
authors.initials: KI
authors.lastname: Tatsumi
authors.forename: Hirokazu
authors.initials: H
authors.lastname: Fujiwara
authors.forename: Susumu
authors.initials: S
authors.lastname: Tanaka
authors.forename: Nobuyuki
authors.initials: N
authors.lastname: Amino
mesh_terms: D002460:Cell Line; D006801:Humans; D017136:Ion Transport / Q000235:genetics / Q000502:physiology; D016297:Mutagenesis, Site-Directed; D017354:Point Mutation; D027981:Symporters / Q000235:genetics* / Q000378:metabolism*; D013961:Thyroid Gland / Q000378:metabolism / Q000502:physiology*; D014162:Transfection; D000099209:Sodium-Iodide Symporters
chemical_list: D027981:Symporters; D000099209:Sodium-Iodide Symporters