Identification and characterization of a Na+-independent neutral amino acid transporter that associates with the 4F2 heavy chain and exhibits substrate selectivity for small neutral D- and L-amino acids
Identification and characterization of a Na+-independent neutral amino acid transporter that associates with the 4F2 heavy chain and exhibits substrate selectivity for small neutral D- and L-amino acids
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DOI：
10.1074/jbc.275.13.9690
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发表时间：
2000-03-31
影响因子：
4.8
通讯作者：
Kanai, Y
中科院分区：
文献类型：
--
作者：
Fukasawa, Y;Segawa, H;Kanai, Y
从小鼠脑中分离出一种编码新型Na+非依赖性中性氨基酸转运蛋白的cDNA。编码的蛋白质，命名为Asc-l（asc型氨基酸转运蛋白1），被发现在结构上与最近鉴定的用于转运系统L、y（+）L、x（C）（-）和B（0，+）的哺乳动物氨基酸转运蛋白相关，所述转运系统通过二硫键连接至II型膜糖蛋白、4F 2重链（4F 2 hc）或rBAT（与B（0，+）氨基酸转运蛋白相关）。Asc-I的功能表达需要4F 2 hc。在非还原条件下的Western印迹分析中，在小鼠脑中检测到118-kDa条带，其似乎对应于Asc-I和4F 2 hc的异二聚体复合物。在还原条件下，条带移至33 kDa，证实Asc-1和4F 2 hc通过二硫键连接。Asc-1介导的转运不依赖于Na+或Cl-的存在。尽管Asc-1显示出与Na+非依赖性宽范围中性氨基酸转运蛋白LATE（Segawa，H.，Yanasawa，Y.，Miyamoto，K.，Takeda，E.，Endou，H.，和Kanai，Y.（1999）J.Biol.Chem.274，19745-19751），Asc-1也表现出独特的底物选择性和转运性质。Asc-1优选小的中性氨基酸如Gly、L-Ala、L-Ser、L-Thr和L-Cys以及α-氨基异丁酸作为底物。Asc-1还以高亲和力转运小中性氨基酸的D-异构体，特别是D-Ser，其是N-甲基-D-天冬氨酸型谷氨酸受体的假定内源性调节剂。Asc-1优先，但不是唯一的，在交换模式。在脑、肺、小肠和胎盘中检测到Asc-1 mRNA。Asc-1的功能特性似乎与Na+非依赖性小中性氨基酸转运系统asc的转运子一致。
A cDNA was isolated from the mouse brain that encodes a novel Na+-independent neutral amino acid transporter. The encoded protein, designated as Asc-l (asc-type amino acid transporter 1), was found to be structurally related to recently identified mammalian amino acid transporters for the transport systems L, y(+)L, x(C)(-) and b(0,+), which are linked, via a disulfide bond, to the type II membrane glycoproteins, 4F2 heavy chain (4F2hc), or rBAT (related to b(0,+) amino acid transporter). Asc-l required 4F2hc for its functional expression. In Western blot analysis in the nonreducing condition, a 118-kDa band, which seems to correspond to the heterodimeric complex of Asc-l and 4F2hc, was detected in the mouse brain. The band shifted to 33 kDa in the reducing condition, confirming that Asc-1 and 4F2hc are linked via a disulfide bond. Asc-1-mediated transport was not dependent on the presence of Na+ or Cl-. Although Asc-1 showed a high sequence homology (66% identity at the amino acid level) to the Na+-independent broad scope neutral amino acid transporter LATE (Segawa, H., Fukasawa, Y., Miyamoto, K., Takeda, E., Endou, H., and Kanai, Y. (1999) J. Biol. Chem. 274, 19745-19751), Asc-1 also exhibited distinctive substrate selectivity and transport properties. Asc-1 preferred small neutral amino acids such as Gly, L-Ala, L-Ser, L-Thr, and L-Cys, and alpha-aminoisobutyric acid as substrates. Asc-1 also transported D-isomers of the small neutral amino acids, in particular D-Ser, a putative endogenous modulator of N-methyl-D-aspartate-type glutamate receptors, with high affinity. Asc-1 operated preferentially, although not exclusively, in an exchange mode. Asc-1 mRNA was detected in the brain, lung, small intestine, and placenta. The functional properties of Asc-1 seem to be consistent with those of a transporter subserving the Na+-independent small neutral amino acid transport system asc.