Sato Y, Arai H, Miyata A, Tokita S, Yamamoto K, Tanabe T, Inoue K
Department of Health Chemistry, Faculty of Pharmaceutical Sciences, University of Tokyo, Japan.
J Biol Chem. 1993 Aug 25;268(24):17705-10.
alpha-Tocopherol transfer protein (alpha TTP) present in rat liver cytosol specifically binds this vitamin and enhances its transfer between separate membranes. We previously reported purification of alpha TTP and showed that two isoforms exist in rat liver, of which the isoelectric points are 5.0 and 5.1, respectively (Sato, Y., Hagiwara, K., Arai, H., and Inoue, K. (1991) FEBS Lett. 288, 41-45). In the present paper, we have isolated a cDNA clone with 2194 base pairs encoding alpha TTP from a rat liver cDNA library. The amino acid sequence deduced from the cDNA contained all the sequences of the peptide fragments obtained by digestion of the purified protein with endoproteinase Lys-C. The isolated cDNA was found to encode the isoform with a pI of 5.0 on the basis of the cross-reactivity of the recombinant protein expressed in Escherichia coli with the isoform-specific monoclonal antibody. From the longest open reading frame of the cloned cDNA, one isoform of rat liver alpha TTP is predicted to be composed of 278 amino acid residues of calculated molecular weight 31,845. Both Western and Northern blot analyses revealed that alpha TTP is expressed exclusively in the liver in rats. alpha TTP has been found to exhibit a structural homology with the cellular retinaldehyde-binding protein present only in visual tissues.
大鼠肝细胞溶质中的α-生育酚转运蛋白（αTTP）特异性结合这种维生素，并增强其在不同膜之间的转运。我们之前报道了αTTP的纯化，并表明大鼠肝脏中存在两种异构体，其等电点分别为5.0和5.1（佐藤洋、萩原健、荒井浩和井上健（1991年）《欧洲生物化学学会联合会快报》288卷，41 - 45页）。在本文中，我们从大鼠肝脏cDNA文库中分离出一个编码αTTP的2194个碱基对的cDNA克隆。从该cDNA推导的氨基酸序列包含了用内肽酶Lys - C消化纯化蛋白所获得的所有肽段序列。基于在大肠杆菌中表达的重组蛋白与异构体特异性单克隆抗体的交叉反应性，发现分离出的cDNA编码pI为5.0的异构体。从克隆cDNA的最长开放阅读框预测，大鼠肝脏αTTP的一种异构体由278个氨基酸残基组成，计算分子量为31,845。蛋白质免疫印迹和Northern印迹分析均显示，αTTP仅在大鼠肝脏中表达。已发现αTTP与仅存在于视觉组织中的细胞视黄醛结合蛋白具有结构同源性。
