The C-terminal domain of the neutral amino acid transporter SNAT2 regulates transport activity through voltage-dependent processes.
The C-terminal domain of the neutral amino acid transporter SNAT2 regulates transport activity through voltage-dependent processes.
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DOI：
10.1042/bj20100507
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发表时间：
2011-03-01
期刊：
影响因子：
--
通讯作者：
Grewer C
中科院分区：
文献类型：
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作者：
Zhang Z;Zander CB;Grewer C
钠偶联中性氨基酸转运蛋白2（SNAT 21）属于溶质转运蛋白SLC 38家族。1个氨基酸分子转运到细胞中由1个Na+离子的共转运驱动。SNAT 2的C-末端的功能意义，这是预测位于细胞外空间，目前是未知的。在这里，我们删除了13个氨基酸残基从SNAT 2的C-末端，并研究了删除转运功能的影响。截短消除了负膜电位（< 0 mV）下的氨基酸转运电流以及底物摄取。然而，在正膜电位下观察到运输电流，表明运输加速，而驱动力降低。在截短的转运蛋白中，膜表达水平正常。与SNAT 2 WT相比，SNAT 2Del C-ter显示出对丙氨酸的3倍更高的表观亲和力和2倍更高的Na+亲和力，表明C-末端对于与SNAT 2的高亲和力底物和Na+相互作用不是必需的。氨基酸转运的pH敏感性在截断后部分保留。与最后的跨膜结构域TM 11之后的截短相反，TM 11的缺失导致无活性的转运蛋白，这很可能是由于细胞表面表达的缺陷。总之，结果表明，SNAT 2的C-末端结构域是一个重要的电压调节器，是一个正常的氨基酸易位过程中所需的生理膜电位。然而，C-末端似乎不参与膜表达的调节。
Sodium-coupled neutral amino acid transporter 2 (SNAT21) belongs to the SLC38 family of solute transporters. Transport of 1 amino acid molecule into the cell is driven by the co-transport of 1 Na+ ion. The functional significance of the C-terminus of SNAT2, which is predicted to be located in the extracellular space, is currently unknown. Here, we removed 13 amino acid residues from the SNAT2 C-terminus and studied the effect of the deletion on transporter function. The truncation abolished amino acid transport currents at negative membrane potentials (< 0 mV), as well as substrate uptake. However, transport currents were observed at positive membrane potentials, demonstrating that transport was accelerated while the driving force decreased. Membrane expression levels were normal in the truncated transporter. SNAT2Del C-ter showed 3-fold higher apparent affinity for alanine, and 2-fold higher Na+ affinity compared to SNAT2WT, suggesting that the C-terminus is not required for high-affinity substrate and Na+ interaction with SNAT2. pH sensitivity of amino acid transport was partially retained after the truncation. In contrast to the truncation after the final trans-membrane domain, TM11, deletion of TM11 resulted in an inactive transporter, most likely due to a defect in cell surface expression. Together, the results demonstrate that the C-terminal domain of SNAT2 is an important voltage regulator that is required for a normal amino acid translocation process at physiological membrane potentials. However, the C-terminus appears not to be involved in regulation of membrane expression.