Identification of a novel system L amino acid transporter structurally distinct from heterodimeric amino acid transporters
Identification of a novel system L amino acid transporter structurally distinct from heterodimeric amino acid transporters
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DOI：
10.1074/jbc.m305221200
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发表时间：
2003-10-31
影响因子：
4.8
通讯作者：
Endou, H
中科院分区：
文献类型：
--
作者：
Babu, E;Kanai, Y;Endou, H
从人肝癌细胞株FLC 4中克隆了一个新的非钠依赖性中性氨基酸转运蛋白的cDNA。当在非洲爪蟾卵母细胞中表达时，命名为LAT 3（L型氨基酸转运蛋白3）的编码蛋白转运中性氨基酸，例如L-亮氨酸、L-异亮氨酸、L-缬氨酸和L-苯丙氨酸。LAT 3介导的转运是Na+非依赖性的，并被2-氨基二环[ 2.2.1]庚烷-2-羧酸抑制，与系统L的性质一致。与已知的与4F 2重链形成异源二聚体复合物的系统L转运蛋白LAT 1和LAT 2不同，LAT 3在爪蟾卵母细胞中自身具有功能。LAT 3的推导的氨基酸序列与POV 1的基因产物相同，POV 1被报道为前列腺癌上调基因，其功能尚未确定，而它与已经鉴定的转运蛋白没有表现出显著的相似性。LAT 3介导的转运的Eadie-Hofstee图是曲线的，而低亲和力组分在生理血浆氨基酸浓度下占主导地位。除氨基酸底物外，LAT 3还识别氨基酸醇。L-亮氨酸的转运是电中性的，由易化扩散介导。相比之下，L-亮氨醇、L-缬氨醇和L-苯丙氨醇在电压钳下具有净正电荷诱导的内向电流，表明这些化合物由LAT 3转运。用N-乙基马来酰亚胺预处理可抑制LAT 3介导的转运，这与最初在肝细胞原代培养中表征的系统L2的性质一致。基于底物选择性、亲和性和N-乙基马来酰亚胺敏感性，LAT 3被认为是一个转运子系统L2。LAT 3应该是一个新的有机溶质转运蛋白家族。
A cDNA that encodes a novel Na+-independent neutral amino acid transporter was isolated from FLC4 human hepatocarcinoma cells by expression cloning. When expressed in Xenopus oocytes, the encoded protein designated LAT3 (L-type amino acid transporter 3) transported neutral amino acids such as L-leucine, L-isoleucine, L-valine, and L-phenylalanine. The LAT3-mediated transport was Na+-independent and inhibited by 2-aminobicyclo[ 2.2.1] heptane-2-carboxylic acid, consistent with the properties of system L. Distinct from already known system L transporters LAT1 and LAT2, which form heterodimeric complex with 4F2 heavy chain, LAT3 was functional by itself in Xenopus oocytes. The deduced amino acid sequence of LAT3 was identical to the gene product of POV1 reported as a prostate cancer-upregulated gene whose function was not determined, whereas it did not exhibit significant similarity to already identified transporters. The Eadie-Hofstee plots of LAT3-mediated transport were curvilinear, whereas the low affinity component is predominant at physiological plasma amino acid concentration. In addition to amino acid substrates, LAT3 recognized amino acid alcohols. The transport of L-leucine was electroneutral and mediated by a facilitated diffusion. In contrast, L-leucinol, L-valinol, and L-phenylalaninol, which have a net positive charge induced inward currents under voltage clamp, suggesting these compounds are transported by LAT3. LAT3-mediated transport was inhibited by the pretreatment with N-ethylmaleimide, consistent with the property of system L2 originally characterized in hepatocyte primary culture. Based on the substrate selectivity, affinity, and N-ethylmaleimide sensitivity, LAT3 is proposed to be a transporter subserving system L2. LAT3 should denote a new family of organic solute transporters.