Investigation of organisms having unique selenium metabolic pathways and its application to bioremediation

硒是一种具有多种生理作用的必需微量元素，它与同源物硫有严格的区别，作为硒半胱氨酸残基被结合到蛋白质的特定位置。在本研究中，我们研究了具有独特硒代谢途径的生物体，并分析了参与硒代谢的新型酶的结构和功能。这表明，在O-phosphosery1-tRNA激酶（PSTK）的催化下，seryl-tRNA由O-phosphosery1-tRNA合成O-phosphosery1-tRNA是古菌硒代半胱氨酸- trna生物合成的必要条件。然而，我们对产甲烷嗜热性Methanocaldococcus jannaschii的PAD、PSTK和硒代半胱氨酸合成酶（sels）的体外研究表明，硒代半胱氨酸1- trna的合成可以通过两个独立的途径进行：一个依赖于PSTK和SelD，另一个依赖于SecS和SelD.2。我们对一种含有独特硒蛋白的细菌进行了研究，发现硫还原地杆菌可能含有一种新的c型细胞色素样硒蛋白。该蛋白命名为GSU2937-GSU2936，其n端区域有5个CXXCH基序，由用于硒代半胱氨酸插入的UGA密码子上游的ORF编码。GSU2937-GSU2936蛋白与多血红素蛋白细胞色素c亚硝酸盐还原酶和羟胺氧化还原酶的序列同源性低于12%，提示其属于一个蛋白家族的新成员。

Selenium is an essential trace element with a variety of physiological role and is strictly discriminated from its cognate sulfur to be incorporated into a specific position of proteins as a selenocysteine residue. In this study, we investigated organisms having unique selenium metabolism pathway and analyzed the structure and function of novel enzymes involved in selenium metabolism.1. It is suggested that the synthesis of O-phosphoseryl-tRNA from seryl-tRNA by the catalysis of O-phosphosery1-tRNA kinase, (PSTK) is essential for the biosynthesis of archaeal selenocystey1-tRNA. However, our in vitro study with PAD, PSTK, and selenocysteine synthase (SecS) from the methanogenic thermophile Methanocaldococcus jannaschii revealed that the synthesis of selenocystey1-tRNA is able to proceed via two independent pathways: one is dependent on PSTK and SelD, and another depends on SecS and SelD.2. We searched far a bacterium with a unique selenoprotein and found that Geobacter sulfurreducens probably contains a novel c-type cytochrome-like selenoprotein. This protein termed GSU2937-GSU2936 has 5 CXXCH motifs in its N-terminal region, which is encoded by the ORF upstream of a UGA codon for selenocysteine insertion. The GSU2937-GSU2936 protein shows only less than 12% sequence identity with cytochrome c nitrite reductase and hydroxylamine oxidoreductase, which are known as multi-heme proteins, suggesting that it belongs to a novel member of a protein family.