Shafqat S, Tamarappoo B K, Kilberg M S, Puranam R S, McNamara J O, Guadaño-Ferraz A, Fremeau R T
Department of Neurobiology, Duke University Medical Center, Durham, North Carolina 27710.
J Biol Chem. 1993 Jul 25;268(21):15351-5.
A cDNA has been isolated from human hippocampus that appears to encode a novel Na(+)-dependent, Cl(-)-independent, neutral amino acid transporter. The putative protein, designated SATT, is 529 amino acids long and exhibits significant amino acid sequence identity (39-44%) with mammalian L-glutamate transporters. Expression of SATT cDNA in HeLa cells induced stereospecific uptake of L-serine, L-alanine, and L-threonine that was not inhibited by excess (3 mM) 2-(methylamino)-isobutyric acid, a specific substrate for the System A amino acid transporter. SATT expression in HeLa cells did not induce the transport of radiolabeled L-cysteine, L-glutamate, or related dicarboxylates. Northern blot hybridization revealed high levels of SATT mRNA in human skeletal muscle, pancreas, and brain, intermediate levels in heart, and low levels in liver, placenta, lung, and kidney. SATT transport characteristics are similar to the Na(+)-dependent neutral amino acid transport activity designated System ASC, but important differences are noted. These include: 1) SATT's apparent low expression in ASC-containing tissues such as liver or placenta; 2) the lack of mutual inhibition between serine and cysteine; and 3) the lack of trans-stimulation. SATT may represent one of multiple activities that exhibit System ASC-like transport characteristics in diverse tissues and cell lines.
已从人脑海马体中分离出一种互补DNA（cDNA），它似乎编码一种新型的钠依赖性、氯非依赖性中性氨基酸转运体。推测的蛋白质命名为SATT，长度为529个氨基酸，与哺乳动物L-谷氨酸转运体具有显著的氨基酸序列同一性（39 - 44%）。SATT cDNA在HeLa细胞中的表达诱导了L-丝氨酸、L-丙氨酸和L-苏氨酸的立体特异性摄取，这种摄取不受过量（3 mM）2-（甲氨基）异丁酸（系统A氨基酸转运体的特异性底物）的抑制。HeLa细胞中SATT的表达并未诱导放射性标记的L-半胱氨酸、L-谷氨酸或相关二羧酸盐的转运。Northern印迹杂交显示，SATT mRNA在人骨骼肌、胰腺和脑中水平较高，在心脏中水平中等，在肝脏、胎盘、肺和肾脏中水平较低。SATT的转运特性类似于被称为系统ASC的钠依赖性中性氨基酸转运活性，但也存在重要差异。这些差异包括：1）SATT在含ASC的组织如肝脏或胎盘中的明显低表达；2）丝氨酸和半胱氨酸之间缺乏相互抑制；3）缺乏反式刺激。SATT可能代表了多种在不同组织和细胞系中表现出类似系统ASC转运特性的活性之一。
