Gladyshev V N, Jeang K T, Wootton J C, Hatfield D L
Section on the Molecular Biology of Selenium, Basic Research Laboratory, NCI, National Institutes of Health, Bethesda, Maryland 20892,
J Biol Chem. 1998 Apr 10;273(15):8910-5. doi: 10.1074/jbc.273.15.8910.
Selenium which occurs in proteins as the amino acid, selenocysteine, is essential for numerous biological processes and for human health. A prominent 75Se-labeled protein detected in human T-cells migrated as a 15-kDa band by SDS-polyacrylamide gel electrophoresis. This protein subunit was purified and subjected to tryptic digestion and peptide sequence analyses. Sequences of tryptic peptides derived from the protein corresponded to a human placental gene sequence containing an open reading frame of 162 residues and a readthrough in-frame TGA codon. Three different peptide sequences of the 15-kDa protein corresponded to a nucleotide sequence located downstream of this codon, suggesting that the T-cell 15-kDa selenoprotein contains a selenocysteine residue encoded by TGA. Post-translational processing of the N-terminal portion of the predicted gene product to give the 15-kDa protein was suggested on the basis of molecular mass, amino acid analysis, and immunoblot assays of the purified protein. The 3'-untranslated region (UTR) of the gene encoding the 15-kDa protein contained a sequence that is very similar to the canonical selenocysteine-inserting sequence element. Computer analysis of transcript map data bases indicated that this gene was located on human chromosome 1. Its coding sequence showed no homology to known protein-encoding genes. The 15-kDa protein gene was expressed as mRNA in a wide range of tissues, with increased levels in the thyroid, parathyroid, and prostate-derived cells as evidenced by searches of partial cDNA sequences in public data bases. Genes corresponding to the 15-kDa selenocysteine-containing protein were found in mice and rats, while the corresponding genes in Caenorhabditis elegans and Brugia malayi contained a cysteine codon in place of TGA. The discovery of a new human selenoprotein provides an additional example of the role of selenium in mammalian systems.
以氨基酸硒代半胱氨酸形式存在于蛋白质中的硒，对众多生物过程和人类健康至关重要。在人T细胞中检测到的一种显著的75Se标记蛋白，经SDS-聚丙烯酰胺凝胶电泳后迁移为一条15 kDa的条带。该蛋白质亚基被纯化，并进行胰蛋白酶消化和肽序列分析。源自该蛋白质的胰蛋白酶肽序列与一个人胎盘基因序列相对应，该基因序列包含一个162个残基的开放阅读框和一个通读的框内TGA密码子。15 kDa蛋白质的三种不同肽序列与位于该密码子下游的核苷酸序列相对应，表明T细胞15 kDa硒蛋白含有由TGA编码的硒代半胱氨酸残基。基于预测基因产物N端部分的分子质量、氨基酸分析和纯化蛋白的免疫印迹分析，推测其经翻译后加工产生了15 kDa的蛋白质。编码15 kDa蛋白质的基因的3'非翻译区（UTR）包含一个与典型的硒代半胱氨酸插入序列元件非常相似的序列。对转录图谱数据库的计算机分析表明，该基因位于人类1号染色体上。其编码序列与已知的蛋白质编码基因没有同源性。通过在公共数据库中搜索部分cDNA序列证明，15 kDa蛋白质基因在多种组织中表达为mRNA，在甲状腺、甲状旁腺和前列腺来源的细胞中表达水平升高。在小鼠和大鼠中发现了与15 kDa含硒代半胱氨酸蛋白质相对应的基因，而秀丽隐杆线虫和马来布鲁线虫中的相应基因含有一个半胱氨酸密码子来代替TGA。一种新的人类硒蛋白的发现为硒在哺乳动物系统中的作用提供了另一个例子。
