The Q267E mutation in the sodium/iodide symporter (NIS) causes congenital iodide transport defect (ITD) by decreasing the NIS turnover number
The Q267E mutation in the sodium/iodide symporter (NIS) causes congenital iodide transport defect (ITD) by decreasing the NIS turnover number
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DOI：
10.1242/jcs.00898
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发表时间：
2004-02-15
影响因子：
4
通讯作者：
Carrasco, N
中科院分区：
文献类型：
--
作者：
De la Vleja, A;Ginter, CS;Carrasco, N
Na+/I- 同向转运蛋白 (NIS) 是一种关键的质膜糖蛋白，介导甲状腺和其他组织中的活性碘化物 (I-) 转运。自从分离编码 NIS 的 cDNA（G. Dai、O. Levy 和 N. Carrasco (1996) Nature 379, 458-460）以来，NIS 中的 10 个突变已被确定为先天性碘转运缺陷（ITD）的原因。其中两个突变（T354P 和 G395R）已在分子水平上得到彻底表征。两种突变 NIS 蛋白均无活性，但正常表达并正确靶向质膜。残基 354 的 β-碳上的羟基对于 NIS 功能至关重要，而 395 位上带电或大侧链的存在会干扰 NIS 功能。我们报告了用大鼠或人 Q267E NIS cDNA 构建体转染的 COS-7 细胞中 Q267E 突变的广泛分子分析。我们使用定点诱变在位置 267 中设计各种残基取代。与之前认为 Q267E NIS 不活跃（可能是由于运输缺陷）的建议相反，我们最终表明 Q267E NIS 具有适度的活性并正确靶向质膜。 Q267E NIS 表现出比野生型 NIS 更低的 I-V-max 值，表明 Q267E NIS 活性水平降低是由于催化速率较低。 Q267E NIS 甚至保留了部分活性，使得这种引起 ITD 的突变体与 T354P 和 G395R NIS 区分开来。 267位除Glu之外的带电残基（任何极性）的存在使NIS失活，而不影响其表达或靶向，但在该位置用中性残基取代与部分活性兼容。
The Na+/I- symporter (NIS) is a key plasma membrane glycoprotein that mediates active iodide (I-) transport in the thyroid and other tissues. Since isolation of the cDNA encoding NIS (G. Dai, O. Levy, and N. Carrasco (1996) Nature 379, 458-460), ten mutations in NIS have been identified as causes of congenital iodide transport defect (ITD). Two of these mutations (T354P and G395R) have been thoroughly characterized at the molecular level. Both mutant NIS proteins are inactive but normally expressed and correctly targeted to the plasma membrane. The hydroxyl group at the beta-carbon of residue 354 is essential for NIS function, whereas the presence of a charged or large side-chain at position 395 interferes with NIS function. We report the extensive molecular analysis of the Q267E mutation in COS-7 cells transfected with rat or human Q267E NIS cDNA constructs. We used site-directed mutagenesis to engineer various residue substitutions into position 267. In contrast to previous suggestions that Q267E NIS was inactive, possibly because of a trafficking defect, we conclusively show that Q267E NIS is modestly active and properly targeted to the plasma membrane. Q267E NIS exhibited lower V-max values for I- than wildtype NIS, suggesting that the decreased level of activity of Q267E NIS is due to a lower catalytic rate. That Q267E NIS retains even partial activity sets this ITD-causing mutant apart from T354P and G395R NIS. The presence of charged residues (of any polarity) other than Glu at position 267 rendered NIS inactive without affecting its expression or targeting, but substitution with neutral residues at this position was compatible with partial activity.