Department of Membrane Biochemistry, Okayama University Graduate School of Medicine, Dentistry, and Pharmaceutical Sciences, Tokyo, Japan.
J Biol Chem. 2010 Aug 20;285(34):26107-13. doi: 10.1074/jbc.M110.122721. Epub 2010 Jun 21.
SLC17A1 protein (NPT1) is the first identified member of the SLC17 phosphate transporter family and mediates the transmembrane cotransport of Na(+)/P(i) in oocytes. Although this protein is believed to be a renal polyspecific anion exporter, its transport properties are not well characterized. Here, we show that proteoliposomes containing purified SLC17A1 transport various organic anions such as p-aminohippuric acid and acetylsalicylic acid (aspirin) in an inside positive membrane potential (Deltapsi)-dependent manner. We found that NPT1 also transported urate. The uptake characteristics were similar to that of SLC17 members in its Cl(-) dependence and inhibitor sensitivity. When arginine 138, an essential amino acid residue for members of the SLC17 family such as the vesicular glutamate transporter, was specifically mutated to alanine, the resulting mutant protein was inactive in Deltapsi-dependent anion transport. Heterologously expressed and purified human NPT1 carrying the single nucleotide polymorphism mutation that is associated with increased risk of gout in humans exhibited 32% lower urate transport activity compared with the wild type protein. These results strongly suggested that NPT1 is a Cl(-)-dependent polyspecific anion exporter involved in urate excretion under physiological conditions.
SLC17A1 蛋白（NPT1）是 SLC17 磷酸转运蛋白家族中第一个被鉴定的成员，它介导卵母细胞中 Na(+)/P(i)的跨膜共转运。虽然该蛋白被认为是一种肾脏多特异性阴离子外排体，但它的转运特性尚未得到很好的描述。在这里，我们展示了含有纯化的 SLC17A1 的质体能够以膜电位差（Deltapsi）依赖的方式转运各种有机阴离子，如对氨基马尿酸和乙酰水杨酸（阿司匹林）。我们发现 NPT1 也能转运尿酸。其摄取特性与 SLC17 家族成员在 Cl(-)依赖性和抑制剂敏感性方面相似。当将 SLC17 家族成员（如囊泡谷氨酸转运体）的必需氨基酸残基精氨酸 138 特异性突变为丙氨酸时，所得突变蛋白在 Deltapsi 依赖的阴离子转运中失活。与野生型蛋白相比，携带与人类痛风风险增加相关的单核苷酸多态性突变的异源表达和纯化的人 NPT1 对尿酸的转运活性降低了 32%。这些结果强烈表明，NPT1 是一种 Cl(-)依赖性多特异性阴离子外排体，参与生理条件下尿酸的排泄。
