Identification and functional characterization of a Na+-independent neutral amino acid transporter with broad substrate selectivity
Identification and functional characterization of a Na+-independent neutral amino acid transporter with broad substrate selectivity
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DOI：
10.1074/jbc.274.28.19745
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发表时间：
1999-07-09
影响因子：
4.8
通讯作者：
Kanai, Y
中科院分区：
文献类型：
--
作者：
Segawa, H;Fukasawa, Y;Kanai, Y
我们已经从大鼠小肠中分离出一个cDNA，它编码一种新的Na+非依赖性中性氨基酸转运蛋白，具有独特的底物选择性和转运特性。编码的蛋白质，命名为L型氨基酸转运蛋白-2（LAT-2），显示出与系统L Na+非依赖性中性氨基酸转运蛋白LAT-1（Kanai，Y.，Segawa，H.，Miyamoto，K.，Uchino，H.，Takeda，E.，和Endou，H.（1998）J.Biol.Chem.273，23629-23632）（50%同一性）和系统y（+）L转运蛋白y（+）LAT-1（47%）和KIAA 0245/y（+）LAT-2（45%）（Torrents，D.，埃斯特韦斯河Pineda，M.，费尔南德斯，E.，Lloberas，J.，施，Y.- B.，Zorzano，A.和Palacin，M.（1998）J.Biol.Chem.273，32437-32445）。LAT-2是一种非糖基化的膜蛋白。它需要4F 2重链，一种II型膜糖蛋白，用于其在爪蟾卵母细胞中的功能表达。LAT-2介导的转运不依赖于Na+或Cl-，并且被系统L特异性抑制剂2-氨基双环-（2，2，1）-庚烷-2-羧酸（BCH）抑制，表明LAT-2是系统L转运蛋白的第二种亚型。与LAT-1相比，LAT-2表现出非常广泛的底物选择性，LAT-1更喜欢具有支链或芳香族侧链的大的中性氨基酸。它运输中性铜氨基酸的所有L-异构体。LAT-2对Tyr、Phe、Trp、Thr、Asn、Ile、Cys、Ser、Leu、瓦尔和Gln表现出较高的亲和力（K-m = 30-50 μ M），对His、Ale、Met和Gly表现出相对较低的亲和力（K-m = 180-300 μ M）。此外，LAT-P介导底物氨基酸的易化扩散，与介导氨基酸交换的LAT-1不同。LAT-2介导的转运通过降低pH水平而增加，在pH 6.25处具有峰值活性，因为K-m值降低而不改变V-max值。由于这些功能特性以及LAT-S在小肠、肾脏、胎盘和脑中的高水平表达，表明LAT-2和4F 2重链的异二聚体复合物参与中性氨基酸的跨细胞转运。上皮和血液组织屏障。
We have isolated a cDNA from rat small intestine that encodes a novel Na+-independent neutral amino acid transporter with distinctive characteristics in substrate selectivity and transport property. The encoded protein, designated L-type amino acid transporter-2 (LAT-2), shows amino acid sequence similarity to the system L Na+-independent neutral amino acid transporter LAT-1 (Kanai, Y., Segawa, H., Miyamoto, K., Uchino, H., Takeda, E., and Endou, H.(1998) J. Biol. Chem. 273, 23629-23632) (50% identity) and the system y(+)L transporters y(+)LAT-1 (47%) and KIAA0245/y(+)LAT-2 (45%) (Torrents, D., Estevez, R., Pineda, M., Fernandez, E., Lloberas, J., Shi, Y.-B., Zorzano, A. and Palacin, M. (1998) J. Biol. Chem. 273, 32437-32445). LAT-2 is a nonglycosylated membrane protein. It requires 4F2 heavy chain, a type II membrane glycoprotein, for its functional expression in Xenopus oocytes. LAT-2-mediated transport is not dependent on Na+ or Cl- and is inhibited by a system L-specific inhibitor, 2-aminobicyclo-(2,2,1)-heptane-2-carboxylic acid (BCH), indicating that LAT-2 is a second isoform of the system L transporter. Compared with LAT-1, which prefers large neutral amino acids with branched or aromatic side chains, LAT-2 exhibits remarkably broad substrate selectivity. It transports all of the L-isomers of neutral cu-amino acids. LAT-2 exhibits higher affinity (K-m = 30-50 mu M) to Tyr, Phe, Trp, Thr, Asn, Ile, Cys, Ser, Leu, Val, and Gin and relatively lower affinity (K-m = 180-300 mu M) to His, Ale, Met, and Gly. In addition, LAT-P mediates facilitated diffusion of substrate amino acids, as distinct from LAT-1, which mediates amino acid exchange. LAT-2-mediated transport is increased by lowering the pH level, with peak activity at pH 6.25, because of the decrease in the K-m value without changing the V-max value. Because of these functional properties and a high level of expression of LAT-S in the small intestine, kidney, placenta, and brain, it is suggested that the heterodimeric complex of LAT-2 and 4F2 heavy chain is involved in the trans-cellular transport of neutral amino acids in epithelia and blood-tissue barriers.